Designing Games
with
Game Maker

Version 7.0
Written by Mark Overmars

What is New

Version 7.0 of Game Maker has a number of important changes over version 6.1. In particular there is a new extension mechanism. Below the most important changes are described.

Incompatibilities

Version 7.0 uses an adapted file format. As a result file names now have the extension .gmk. The new version can though still read .gm6 files created with the previous version and it is fully compatible with such files.

There is a minor incompatibility in the use of room transitions. In previous version transitions could also be used between frames in the same room. This is not longer possible. Transitions can only be used between rooms. But the number of transitions is considerably extended.

Extension packages

The major improvement of version 7.0 of Game Maker is the mechanism of extension packages that has been introduced. Extension packages can either add new collections of actions to Game Maker or they add new functions using DLL or GML files. A new item has been added to the resource list in which the user can indicate which extension packages to use. These are then automatically integrated in the system. Actions are shown in the object form and functions are colorcoded in the script editor, show in the list of functions. Extension packages can have help files that are automatically included in the help menu. Also all required files are automatically added to the game executables.

Three extension package are default provided.

• GM Printing. Adds a large number of functions for printing shapes, text, sprites, screenshots, etc. and contains dialogs to select the printer and set printer preferences.
• GM Transitions. Adds over 60 room transitions to the program.
• GM Windows Dialogs. Adds functions to create most of the standard Windows dialogs for messages, input boxes, file selection, etc.

It is rather easy to create your own extension packages. There is a special program available for this. See the page http://www.yoyogames.com/extensions for more information on how to do this. The extension mechanism sort of replaces and enhances the current DLL mechanism (which remains available).

Publishing games

A publish button has been added to the toolbar. This will take you to our site were you can easily make your finished game available to the public.

Splash screens

The splash screen mechanism has been considerably enhanced. Splash screens, like videos and images are now default shown in the main game window. There are many new options, e.g. to change the scaling. Also other image formats can be used. And rich text files can now contain images.

Game information

The game information is now default shown in the game window and can be closed with the close button.

Separate close button event

It can now be indicated whether or not the Close button must behave like the escape key or not. If not, there is a new event in the Other events that happens when the user clicks on the Close button. So you can now assign different behavior to the Close button and to the escape key.

Room transitions

The room transition mechanism is changed and extended, giving you more control over the transitions and adding many new transitions, like fade-ins, pushing the images, blending room images, rotations, etc. It is now even possible to define your own scripts to do the transitions (but this is rather advanced stuff). An extension package with additional room transitions is provided.

Data structures

A number of additional functions have been provided to deal with data structures. For example, data structures can now be copied, there are functions to write data structures to a string and read them back. This string can then used to e.g. save the datastructure to a file. Also there are more functions for grid data structures to e.g. copy and add parts of grids.

Including files

The mechanism to include files in the executables has been considerably extended. For each file it can now be indicated under what filename it must be stored and where it must be stored. There is a choice now whether or not to include the files in the editable version of the game. Also there are functions to export the files at a different moment than the start of the game.

Adding sprites and backgrounds with alpha channel

There are now functions sprite_add_alpha() and sprite_replace_alpha() to add or replace a sprite from a file that has an alpha channel (such as png files) to get nicer transparancy effects. Similar functions exist for backgrounds.

New registration mechanism

Version 7 uses a new registration mechanism. The free and registered version are now called the Lite and Pro Edition. There is an improved online purchase process that immediately upgrades the program after the payment is made. Old version 5 and 6 registration keys can be exchanged for version 7 activation codes.

Other changes

There are a number of other changes and additions. Here are some of the important ones.

• The selected direction(s) in the Move Fixed action are now colored red.
• When running a game the loading bar is shown considerably earlier such that it is clear the game is running.
• Renamed all actions for more easy reference (compatible with the book).
• When adding or replacing sprites and backgrounds or when using splash images, many different file formats can now be used, including jpg, tif, bmp, gif, png, etc.
• In the image editor there now is a command (Ctrl-A) to select the whole image.
• A toolbar button was added on the main form to save the game as stand-alone executable.
• In the constants list in game settings, buttons were added to move them up or down in the list and to insert a constant above the current one.
• Function message_position(-1,-1) now sets the message box to the screen center.
• Print buttons were added in the script and code editor.
• Save and print buttons were added to the debug info forms.
• Events were added that happen when an instance lies outside a view or intersects the view boundary.
• The form showing errors in the game is enhanced and allows for copying them to the clipboard.
• Functions random_set_seed(seed), random_get_seed(), and randomize() were added.
• In the image editor you can now jump to next/prev subimage of a sprite.
• Global variables can now be declared using the keyword globalvar. After this declaration it is no longer necessary to add the word global and a dot in front of them.
• During game play F9 now takes a screenshot unless this is switched off in the global game settings.
• Added functions draw_line_width(x1,y1,x2,y2,w) and draw_line_width_color(x1,y1,x2,y2,w,col1,col2) to draw lines with a width.
• d3d_start() and d3d_end() now return whether successful.
• You can now set the variable cursor_sprite to automatically draw a sprite at the cursor location.
• Increased the maximum number of arguments to DLL functions to 16.
• In the options under Other you can now indicate version information for the game that will be embedded in the executable.
• Added functions sprite_save(ind,subimg,fname) and background_save(ind,fname) to save the resources as bitmaps.
• Added a variable program_directory that stores the location of the game executable.
• Added a constant c_orange.
• ...

Corrected bugs

The following bugs were corrected.

• Solved the problem that sometimes led to corrupted files. Version 7 will read files that were previously marked as being corrupt.
• A problem with limited real precision was solved. This hould also solve problems with functions dealing with the date and time.
• A bug in timelines was corrected when duplicating to an earlier moment.
• Bitwise assignments now work correctly and give no syntax errors.
• show_message() actions and function now keep the box in the screen center.
• Using snow effects and explosion effects together now works correctly.
• A vulnerability to obtain information from a running game was removed.
• Debug info forms no longer keep jumping to the top position.
• Game Maker and the created games now work correctly under Windows Vista. As a result though the file size of the games has been considerably increased.
• When copying something in the code editor the font is now correct and color coding is applied.
• Backgrounds no longer loose their settings when a new image is loaded.
• An off-by-one error in drawing filled rectangles was solved.
• The game window is now made visible before executing create events.
• Solved a bug in the function median().
• Solved a crash when resizing a grid.
• Comparing and finding values in grids now works correctly for string values.
• Editing a non-transparent sprite will no longer sometimes turn it transparent in the preview.
• Solved a bug in collision checking with scaled instances.
• Solved a bug in collision checking with e.g. lines and rectangles that were not on integer coordinates.
• Function file_bin_open now create the file if it does not yet exist.
• Added checks in the object_set_parent function to avoid cycles.
• Solved an error in the bounce action with diagonal bounces.
• Corrected a bug in the rain effect when the room was higher than 1000 pixels.
• Corrected a bug that instances without sprites would contstantly get Outside Room events.
• Corrected a bug when dragging actions between Object and Timeline form (it is no longer possible).
• Increase the minimal height of the background form to make it impossible to hide the OK button.
• Corrected a bug with addressing variables in an instance after it changed object during the same step.
• Corrected a bug that (de-)activating instances without a sprite could work wrong.
• Corrected an error in drawing a path with 0 length.
• Solved a bug that the Exit Event action inside a Repeat block did not exit the event.
• Corrected the position of the loading bar for the game.
• Corrected an error in removing instance outside a room in the room editor.
• ...

Using Game Maker

Game Maker is an easy to use program for creating your own computer games. This section of the help file gives you all the information you need for creating your first games. Later sections will discuss more advanced topics, how to finish and distribute your game, and the built-in programming language GML.

So you want to create your own computer games

Playing computer games is fun. But it is actually more fun to design your own computer games and let other people play them. Unfortunately, creating computer games is not easy. Commercial computer games you buy nowadays typically take one to three years of development with teams of anywhere between 10 and 50 people. Budgets easily reach millions of dollars. And all these people are highly experienced: programmers, art designers, sound technicians, etc.

So does this mean that it is impossible to create your own computer games? Fortunately no. Of course you should not expect to create your own Quake or Age of Empires within a few weeks. But that is also not necessary. Simpler games, like Tetris, Pacman, Space Invaders, etc. are also fun to play and a lot easier to create. Unfortunately they still require good programming skills to handle the graphics, sounds, user interaction, etc.

But here comes Game Maker which was written to make it a lot easier to create such games. There is no need to program. An intuitive and easy to use drag-and-drop interface allows you to create your own games very quickly. You can import and create images, sprites (animated images) and sounds and use them. You can easily define the objects in your game and indicate their behavior, and you can define appealing rooms with scrolling backgrounds in which the game takes place. And if you want full control there is actually an easy-to-use programming language built into Game Maker that gives you full control over what is happening in your game.

Game Maker focuses on two-dimensional games. So it is not meant to create 3D worlds like Quake, even though there is some limited functionality for 3D graphics. But don’t let this put you down. Many great games, like Age of Empires, the Command & Conquer series, and Diablo use two-dimensional sprite technology, even though they look very 3-dimensional. And designing two-dimensional games is a lot easier and faster.

Game Maker comes in two editions, the Lite Edition and the Pro Edition. The Lite Edition can be used free of charge but it is limited in its functionality and will display popup messages. You can though freely distribute the games you create with it, you can even sell them if you like. See the enclosed license agreement for more details. You are strongly encouraged to upgrade your copy of Game Maker to the Pro Edition. It will considerably extend the functionality of Game Maker and it will remove the logo when running games. This will also support the further development of Game Maker.

This document will tell you all you need to know about Game Maker and how you can create your own games with it. Please realize that, even with a program like Game Maker, designing computer games is not completely effortless. There are too many aspects that are important: game play, graphics, sounds, user interaction, etc. Start with easy examples and you will realize that creating games is great fun. Also check the web site

http://www.yoyogames.com/

for lots of examples, tutorials, ideas, and links to other site and forums. And soon you will become a master game maker yourself. Enjoy.

Installation

You probably already did this but if not, here is how to install Game Maker. Simply run the program gmaker.exe. Follow the on-screen instructions. You can install the program anywhere you like but it is best to follow the default suggestions given. Once installation is completed, in the Start menu you will find a new program group where you can start Game Maker and read the help file.

The first time you run Game Maker you are asked whether you want to run the program in Simple or Advanced mode. If you have not used a game creation program before and you are not an experienced programmer, you had better use simple mode (so select No). In simple mode fewer options are shown. You can easily switch to advanced mode later using the appropriate item in the File menu.

Requirements

Game Maker requires a modern Pentium PC running Windows 2000, Me, XP, Vista, or later. A DirectX 8 (or later) compatible graphics card with at least 32MB of memory is required for most created games. It requires a screen resolution of at least 800x600 and 65000 (16-bit) colors. Also a DirectX 8 compatible sound card is required. Make sure you have the most recent drivers installed. Game Maker requires DirectX version 8.0 or later to be installed on your computer. (You can download the newest version of DirectX from the Microsoft website at: http://www.microsoft.com/windows/directx/.) When designing and testing games, the memory requirements are pretty high (at least 128 MB and preferably more, also depending on the operating system). When just running games, the memory requirements are less severe and depend a lot on the type of game.

Upgrading to the Pro Edition

Game Maker comes in two editions, the Lite Edition and the Pro Edition.

The Lite Edition is meant for those that take their first steps on the path of developing games. It can be used for free but is limited in its functionality. Also it shows a popup logo when running games and will regularly remind you of upgrading the program. When you are using Game Maker regularly you are strongly recommended to upgrade it to the Pro Edition.

The Pro Edition contains considerably more functionality and does not display any logos or popup messages. More precisely, the Pro Edition has the following additional functionality:

• No Game Maker logo is shown when running a game.
• No regular popups remind you of upgrading.
• You can use rotated, color blended and translucent sprites.
• There are additional actions for e.g. CD music, rotated text, and colorized shapes.
• You can use special sound effects and positional sound.
• You can create splash screens with movies, images, texts, etc.
• There is a particle system to create explosions, fireworks, flames, rain, and other effects.
• A number of advanced drawing functions are available, for example colorized text and textured polygons.
• It is possible to create 3D games using functions for 3D graphics.
• It is possible to create multiplayer games that can be played over a network.
• You can define your own room transitions.
• You can use functions to create, load, and modify resources (sprites, backgrounds, etc.) while the game is running.
• There is a collection of functions to create and use data structures.
• There are functions for motion planning.
• You get the possibility to include additional files in the game executables that can be used when the game is run.
• The Pro Edition can easily be extended using extension package. These can be made by everybody and will in general be provided free of charge.
• Three such extension packages are included adding many room transitions, windows dialogs, and printing facilities.

Upgrading the Lite Edition to the Pro Edition costs only 15 Euro or US $20 (subject to change). This is a one-time fee that will at least be valid for all versions 7.x of Game Maker.

When you are running the Lite Edition, whenever you start Game Maker the following form will be shown:

You can also get to this form by choosing Upgrade from the Help menu. You can use this form to upgrade to the Pro Edition. There are a number of ways to do this.

The easiest way is to purchase the upgrade online. To this end press the button Purchase Online. You will be brought to a webpage were you can make you payment either by credit card or through PayPal. The payment will be handled by the company SoftWrap that is our authorized payment processor. Once you made the payment the software will immediately be upgraded to the Pro Edition without any further action from your side. Carefully save (and print) the confirmation you receive as it contains your purchase reference that you might need later if you want to reinstall the software.

If you purchased Game Maker before (and hence, have an activation code or a previous purchase reference) press the button Enter Activation Code. You will be brought to a webpage where you can either enter your activation code or your purchase reference from your previous payment. Here you can also retrieve your license if you lost it. After you filled in the correct information Game Maker will be upgraded to the Pro Edition. Note that you must have an Internet connection for activation.

If you want to pay for your license in a different way, or if you want to order an activation code to give as a present or use on a different machine, press the button Go to Upgrade Webpage or go yourself to the following webpage:

http://www.yoyogames.com/upgrade

Here you find instructions. Also you find information about ordering site license and about discounts. Moreover you find the answers to many questions related to upgrading.

If you have a registration key for version 5 or 6 of Game Maker you can exchange this for a version 7 activation code. Instructions for this are given on the same webpage.

The global idea

Before delving into the possibilities of Game Maker it is good to get a feeling for the global idea behind the program. Games created with Game Maker take place in one or more rooms. (Rooms are flat, not 3D, but they can contain 3D-looking graphics.) In these rooms you place objects, which you can define in the program. Typical objects are the walls, moving balls, the main character, monsters, etc. Some objects, like walls, just sit there and don’t do anything. Other objects, like the main character, will move around and react to input from the player (keyboard, mouse, and joystick) and to each other. For example, when the main character meets a monster he might die. Objects are the most important ingredients of games made with Game Maker, so let us talk a bit more about them.

First of all, most objects need some image to make them visible on the screen. Such images are called sprites. A sprite is often not a single image but a set of images that are shown one after the other to create an animation. In this way it looks like the character walks, a ball rotates, a spaceship explodes, etc. During the game, the sprite for a particular object can change. (So the character can look different when it walks to the left or to the right.) You can create you own sprites in Game Maker or load them from files (e.g. animated GIF’s).

Certain things will happen to objects. Such happenings are called events. Objects can take certain actions when events happen. There are a large number of different events that can take place and a large number of different actions that you can let your objects take. For example, there is a creation event when the object gets created. (To be more precise, when an instance of an object gets created; there can be multiple instances of the same object.) For example, when a ball object gets created you can give it some motion action so that it starts moving. When two objects meet, you get a collision event. In such a case you can make the ball stop or reverse direction. You can also play a sound effect. To this end Game Maker lets you define sounds. When the player presses a key on the keyboard there is a keyboard event, and the object can take an appropriate action, like moving in the direction indicated. We hope you get the idea. For each object you design, you can indicate actions for various events; in this way defining the behavior of the object.

Once you have defined your objects it is time to define the rooms in which they will live. Rooms can be used for levels in your game or to check out different places. There are actions to move from one room to another. Rooms, first of all, have a background. This can be a simple color or an image. Such background images can be created in Game Maker or you can load them from files. (The background can do a lot of things but for the time being, just consider it as something that makes the rooms look nice.) Next, you can place the objects in the room. You can place multiple instances of the same object in a room. So, for example, you need to define just one wall object and can use it at many places. Also you can have multiple instances of the same monster objects, as long as they have the same behavior.

Now you are ready to run the game. The first room will be shown and objects will come to life because of the actions in their creation events. They will start reacting to each other due to actions in collision events and they can react to the player using the actions in keyboard or mouse events.

So in summary, the following things (often called resources) play a crucial role:

• objects: which are the true entities in the game
• rooms: the places (levels) in which the objects live
• sprites: (animated) images that are used to represent the objects
• sounds: these can be used in games, either as background music or as effects
• backgrounds: the images used as background for the rooms

There are actually a number of other types of resources: paths, scripts, fonts, and time lines. These are important for more complicated games. You will only see them when you run Game Maker in advanced mode. They will be treated in the advanced chapters later in this document.

Let us look at an example

It is good first to have a look at how to make a very simple example. We assume here that you run Game Maker in simple mode. The first step is to describe the game we want to make. (You should always do this first; it will save you a lot of work later.) The game will be very simple: There is a blue ball bouncing around between some red walls. The player should try to click on the ball with the mouse. Each time he succeeds he gets a point.

As can be seen, we will require two different objects: the ball and the wall. We will also need two different sprites: one for the wall object and one for the ball object. Finally, we want to hear some sound when we succeed in clicking on the ball with the mouse. We will just use one room in which the game takes place. (If you don't want to make the game yourself you can load it from the Examples folder under the name hit the ball.gmk.)

Let us first make the sprites. From the Resources menu select Create Sprite (you can also use the appropriate button on the toolbar). A form will open. In the Name field type “wall”. Select the Load Sprite button and choose an appropriate image. That is all, and you can close the form. In the same way, create a ball sprite.

Next, we make the sound. From the Resoources menu select Create Sound. A different form opens. Give the sound a name and choose Load Sound . Pick something appropriate and check whether it is indeed a nice sound by pressing the play button. If you are satisfied, close the form.

The next step is to create the two objects. Let us first make the wall object. Again from the Resources menu choose Create Object. A form will open that looks quite a bit more complex than the ones we have seen so far. At the left there is some global information about the object. Give the object an appropriate name, and from the drop down menu pick the correct wall sprite. Because a wall is solid, you should check the box labeled Solid. That is all for the moment. Again create a new object, name it ball, and give it the ball sprite. We don't make the ball solid. For the ball, we need to define some behavior. In the middle you see an empty list of events. Below it there is a button labeled Add Event. Press it and you will see all possible events. Select the Create event. This is now added to the list of events. At the far right you see all the possible actions in a number of groups. From the move group choose the action with the 8 red arrows and drag it to the action list in the middle. This action will make the object move in a particular direction. Once you drop it in the action list, a dialog pops up in which you can indicate the direction of motion. Select all 8 arrows to choose a random direction. You can leave the speed as 8. Now close the dialog. So now the ball will start moving at the moment it is created. Secondly, we have to define what should happen in the case of a collision event with the wall. Again, press Add Event. Click on the button for collision events and in the drop down menu select the wall object. For this event we need the bounce action. (You can see what each action does by holding the mouse cursor still above it.) Finally, we need to define what to do when the user presses the left mouse button on the ball. Add the corresponding event and select the left mouse button from the pop-up menu. For this event we need a few actions: one to play a sound (can be found in the group of main1 actions) and one to change the score (in the group score) and two more to let the ball jump to a new random position and moving in a new direction (in the same way as in the creation event). For the sound action, select the correct sound. For the score action, type in a value of 1 and check the Relative box. This means that 1 is added to the current score. (If you make a mistake you can double click the action to change its settings.)

Our objects are now ready. What remains is to define the room. Create a new room in the game, again from the Resources menu. At the right you see the empty room. At the left you find some tabs, one for setting the background, one for setting some global properties like the width and height of the room, and one where you can add instances to the room. At the bottom you can select an object in the pop-up menu. By clicking in the room you can place instances of that object there. You can remove instances using the right mouse button. Create a nice boundary around the room using the wall object. Finally, place 1 or 2 ball objects in the room. Our game is ready.

Now it is time to test our game. Press the Run button (the green triangle on the button bar at the top of the window) and see what happens. If you made no mistakes, the ball starts moving around. Try clicking on it with the mouse and see what happens. You can stop the game by pressing the <Esc> key. You can now make further changes.

Congratulations. You made your first little game. But it is now time to learn a bit more about Game Maker.

The global user interface

When you start Game Maker the following form is shown:

(Actually, this is what you see when you run Game Maker in simple mode. In advanced mode a number of additional items are shown.) At the left, you see the different resources mentioned above: Sprites, Sounds, Backgrounds, Objects, Rooms and two more: Game Information and Global Game Settings. At the top there is the familiar menu and toolbar. In this chapter we will describe briefly the various menu items, buttons, etc. In the later chapters we discuss a number of them in detail. Note that many things can be achieved in different ways: by choosing a command from the menu, by clicking a button, or by right clicking on a resource.

File menu

In the file menu you can find some of the usual commands to load and save files, plus a few special ones:

• New. Choose this command to start creating a new game. If the current game was changed you are asked whether you want to save it. There is also a toolbar button for this.
• Open. Opens a game file. Game Maker files have the extension .gmk. You can also open old .gm6 files. If you want to open .gmd files created with version 5 of Game Maker you must select the appropriate file type at the bottom of the dialog. These might though not work correctly in the new version.) There is a toolbar button for this command. You can also open a game by dragging the file into the Game Maker window.
• Recent Files. Use this submenu to reopen game files you recently opened.
• Save. Saves the game design file under its current name. If no name was specified before, you are asked for a new name. You can only use this command when the file was changed. Again, there is a toolbar button for this.
• Save As. Saves the game design file under a different name. You are asked for a new name.
• Create Executable. Once your game is ready you will probably want to give it to others to play. Using this command you can create a stand- alone version of your game. This is simply an executable that you can give to other people to run.
• Advanced Mode. When clicking on this command Game Maker will switch between simple and advanced mode. In advanced mode additional commands and resources are available.
• Exit. Probably obvious. Press this to exit Game Maker . If you changed the current game you will be asked whether you want to save it.

Edit menu

The edit menu contains a number of commands that relate to the currently selected resource (object, sprite, sound, etc.). Depending on the type of resource some of the commands may not be available.

• Insert resource. Inserts a new instance of the currently selected type of resource before the current one. A form will open in which you can change the properties of the resource. This will be treated in detail in the following chapters.
• Duplicate. Makes a copy of the current resource and adds it. A form is opened in which you can change the resource.
• Delete. Deletes the currently selected resource (or group of resources). Be careful. This cannot be undone. You will, though, be warned.
• Rename. Gives the resource a new name. This can also be done in the property form for the resource. Also, you can select the resource and then click on the name.
• Properties. Use this command to bring up the form to edit the properties. Note that all the property forms appear within the main form. You can edit many of them at the same time. You can also edit the properties by double clicking on the resource.

Note that all these commands can also be given in a different way. Right- click on a resource or resource group, and the appropriate pop-up menu will appear.

Resources menu

In this menu, you can create new resources of each of the different types. Note that for each of them there is also a button on the toolbar and a keyboard shortcut.

Run menu

This menu is used to run the game. There are two ways to run a game.

• Run normally. Runs the game as it would normally run. The game is run in the most efficient way and will look and act as in an executable game.
• Run in Debug mode. Runs the game in debug mode. In this mode you can check certain aspects of the game and you can pause and step through it. This is useful when something goes wrong but is a bit advanced.

Once your game is finished, you can create a stand-alone executable of the game using the command in the file menu.

Window menu

In this menu you find some of the usual commands to manage the different property windows in the main form:

• Cascade. Cascade all the windows such that each of them is partially visible.
• Arrange Icons. Arrange all the iconified property windows. (Useful in particular when resizing the main form.)
• Close All. Close all the property windows, asking the user whether or not to save the changes made.

Help menu

Here you find some commands to help you:

• Contents. Use this command to show this help file.
• Online Help. This command will bring you to a location on the website where you can obtain all sorts of additional help and where you can also download some tutorials.
• Upgrade. You can use this command to upgrade the Lite Edition of Game Maker to the Pro Edition. The Pro Edition has many aditional features. Here you can find information on how to upgrade the program. If you did upgrade it you can use this command to enter the registration key you received.
• Web site. Connects you to the Game Maker website where you can find information about the most recent version of Game Maker and collections of games and resources for Game Maker. We recommend that you check out the site at least once a month.
• Forums. This command will bring you to the forums where users help each other with many aspects of Game Maker.
• About Game Maker. Gives some short information about this version of Game Maker.

The resource explorer

At the left of the main form you find the resource explorer. Here you will see a tree-like view of all resources in your game. It works in the same way as the Windows Explorer, and you are most likely familiar with it. If an item has a + sign in front of it you can click on the sign to see the resources inside it. By clicking on the - sign these disappear again. You can change the name of a resource (except the top level ones) by selecting it (with a single click) and then clicking on the name. Double click on a resource to edit its properties. Use the right mouse button to access the same commands as in the Edit menu.

You can change the order of the resources by clicking on them with the mouse and holding the mouse button pressed. Now you can drag the resource to the appropriate place. (Of course the place must be correct. You cannot drag a sound into the list of sprites.)

Defining sprites

Sprites are the visual representations of all the objects in the game. A sprite is either a single image, drawn with any drawing program you like, or a set of images that, when played one after another, looks like an animated motion. For example, the following four images form a sprite for a Pacman moving to the right.

When you make a game you normally start by collecting a set of nice sprites for the objects in your game. Many collections of interesting sprites can be found on the Game Maker website. Other sprites can be found on the web, normally in the form of animated gif files.

To create a sprite, choose the item Create Sprite from the Resources menu, or use the corresponding button on the toolbar. The following form will pop up.

At the top you can indicate the name of the sprite. All sprites (and all other resources) have a name. it's best to give each sprite a descriptive name. Make sure all resources get different names. Even though this is not strictly required, you are strongly advised to use only letters and digits and the underscore symbol (_) in a name of a sprite (and any other resource) and to let it start with a letter. In particular don't use the space character. This will become important once you start using code.

To load a sprite, click on the button Load Sprite. A standard file dialog opens in which you can choose the sprite. Game Maker can load many different graphics files. When you load an animated gif, the different subimages form the sprite images. Once the sprite is loaded the first subimage is shown on the right. When there are multiple sub- images, you can cycle through them using the arrow buttons.

The checkbox labeled Transparent indicates whether the rectangular background of the sprite image should be considered as being transparent. Most sprites are transparent. The background is determined by the color of the leftmost bottommost pixel of the image. So make sure that no pixel of the actual image has this color. (Note that gif files often define their own transparency color. This color is not used in Game Maker.)

With the button Edit Sprite you can edit the sprite, or even create a completely new sprite.

Sounds and music

Most games have certain sound effects and some background music. Many useful sound effects can be found on the Game Maker website. Many more can be found on other places on the web.

To create a sound resource in your game, use the item Create Sound in the Resources menu or use the corresponding button on the toolbar. The following form will pop up.

To load a sound, press the button labeled Load Sound. A file selector dialog pops up in which you can select the sound file. There are two types of sound files, wave files and midi files. Wave files are used for short sound effects. They use a lot of memory but play instantaneously. Use these for all the sound effects in your game. Midi files describe music in a different way. As a result they use a lot less memory, but they are limited to instrumental background music. Also, default only one midi sound can play at any time.

Once you load a music file you can listen to the sound using the play button. There is also a button Save Sound to save the current sound to a file. This button is not really required but you might need it if you lost the original sound.

Backgrounds

The third type of basic resource is backgrounds. Backgrounds are usually large images that are used as backgrounds (or foregrounds) for the rooms in which the game takes place. Often background images are made in such a way that they can tile an area without visual cracks. In this way you can fill the background with some pattern. A number of such tiling backgrounds can be found on the Game Maker website. Many more can be found at other places on the web.

To create a background resource in your game, use the item Create Background in the Resources menu or use the corresponding button on the toolbar. The following form will pop up.

Press the button Load Background to load a background image. Game Maker supports many image formats. Background images cannot be animated! The checkbox Transparent indicates whether or not the background is partially transparent. Most backgrounds are not transparent so the default is not. As transparency color the color of the leftmost bottommost pixel is used.

You can change the background or create a new one using the button Edit Background.

Be careful with large backgrounds. A number of graphics cards cannot handle images that are larger than the screen. So preferably keep your background images smaller than 1024x1024.

Defining objects

With the resources you have seen so far you can add some nice images and sounds to the game, but they don't do anything. We now come to the most important resource of Game Maker, the objects. Objects are entities in the game that do things. Most of the time they have a sprite as a graphical representation so that you see them. They have behavior because they can react to certain events. All things you see in the game (except for the background) are objects. (Or to be more precise, they are instances of objects.) The characters, the monsters, the balls, the walls, etc. are all objects. There might also be certain objects that you don't see but which control certain aspects of the game play.

Please realize the difference between sprites and objects. Sprites are just (animated) images that don't have any behavior. Objects normally have a sprite to represent them but objects have behavior. Without objects there is no game!

Also realize the difference between objects and instances. An object describes a certain entity, e.g. a monster. There can be multiple instances of this object in the game. When we talk about an instance we mean one particular instance of the object. When we talk about an object we mean all the instances of this object.

To create an object in your game, choose Create Object from the Resources menu. The following form will appear:

This is rather complex. At the left there is some general information about the object. In the middle there is the list of events that can happen to the object. At the right there are the different actions the object can perform. Events and actions will be discussed in the coming chapters.

As always, you can (and should) give your object a name. Next you can choose the sprite for the object. To this end, click with the left mouse button on the sprite box or the menu button next to it. A menu will pop-up with all the available sprites. Select the one you want to use for the object. If you do not have a sprite yet, you can click the button New to create a new sprite resource and change it. Also, when you select a resource there will be a button Edit here that you can use to change the sprite. This is faster than first finding the resource in the list of resources and then indicating you want to edit it.

Below this there are two check boxes. Visible indicates whether instances of this object are visible. Clearly, most objects are visible, but sometimes it is useful to have invisible objects. For example, you can use them for waypoints for a moving monster. Invisible objects will react to events and other instances do collide with them. The box labeled Solid indicates whether this is a solid object (like a wall). Collisions with solid objects are treated differently from collisions with non-solid objects. You are strongly advised to use Solid only for object that are not moving.

Events

Game Maker uses what is called an event driven approach. This works as follows. Whenever something happens in the game the instances of the objects get events (kind of messages telling that something has happened). The instances can then react to these messages by executing certain actions. For each object you must indicate to which events it responds and what actions it must perform when the event occurs. This may sound complicated but is actually very easy. First of all, for most events the object does not have to do anything. For the events where something must be done you can use a very simple drag-and-drop approach to indicate the actions.

In the middle of the object property form there is a list of events to which the object must react. Initially it is empty. You can add events to it by pressing the button labeled Add Event. A form will appear with all different types of events. Here you select the event you want to add. Sometimes a menu pops up with extra choices. For example, for the keyboard event you must select the key. Below you find a complete list of the different events plus descriptions. One event in the list will be selected. This is the event we are currently changing. You can change the selected event by clicking on it. At the right there are all the actions represented by little icons. They are grouped in a number of tabbed pages. In the next chapter you will find descriptions of all the actions and what they do. Between the events and the actions there is the action list. This list contains the actions that must be performed for the current event. To add actions to the list, drag them with your mouse from the right to the list. They will be placed below each other, with a short description. For each action you will be asked to provide a few parameters. These will also be described in the next chapter. So after adding a few actions the situation might look as follows:

Now you can start adding actions to another event. Click on the correct event with the left mouse button to select it and drag actions in the list.

You can change the order of the actions in the list again using drag-and-drop. If you hold the <Alt> key while dragging, you make a copy of the action. You can even use drag-and-drop between action lists for different objects. When you click with the right mouse button on an action, a menu appears in which you can delete the selected action (can also be done by using the <Del> key) or copy and paste actions. (You can select multiple actions for cutting, copying, or deleting by holding the <Shift> key of <Ctrl> key. Press <Ctrl><A> to select all actions.) When you hold your mouse at rest above an action, a longer description is given of the action. See the next chapter for more information on actions.

To delete the currently selected event together with all its actions press the button labeled Delete. (Events without any actions will automatically be deleted when you close the form so there is no need to delete them manually.) If you want to assign the actions to a different event (for example, because you decided to use a different key for them) press the button labeled Change and pick the new event you want. (The event should not be defined already!) Using the menu that pops up when right-clicking on the event list, you can also duplicate an event, that is, add a new event with the same actions.

As indicated above, to add an event, press the button Add Event. The following form pops up:

Here you select the event you want to add. Sometimes a menu pops up with extra choices. Here is a description of the various events. (Again remember that you normally use only a few of them.)

Create event
This event happens when an instance of the object is created. It is normally used to set the instance in motion and/or to set certain variables for the instance.

Destroy event
This event happens when the instance is destroyed. To be precise, it happens just before it is destroyed, so the instance does still exist when the event is executed! Most of the time this event is not used but you can for example use it to change the score or to create some other object.

Alarm events
Each instance has 12 alarm clocks. You can set these alarm clocks using certain actions (see next chapter). The alarm clock then ticks down until it reaches 0 at which moment the alarm event is generated. To indicate the actions for a given alarm clock, you first need to select it in the menu. Alarm clocks are very useful. You can use them to let certain things happen from time to time. For example a monster can change its direction of motion every 20 steps. (In such cases one of the actions in the event must set the alarm clock again.)

Step events
The step event happens every step of the game. Here you can put actions that need to be executed continuously. For example, if one object should follow another, here you can adapt the direction of motion towards the object we are following. Be careful with this event though. Don't put many complicated actions in the step event of objects of which there are many instances. This might slow the game down. To be more precise, there are three different step events. Normally you only need the default one. But using the menu you can also select the begin step event and the end step event. The begin step event is executed at the beginning of each step, before any other events take place. The normal step event is executed just before the instances are put in their new positions. The end step event is executed at the end of the step, just before the drawing. This is typically used to change the sprite depending on the current direction.

Collision events
Whenever two instances collide (that is, their sprites overlap) a collision event appears. Well, to be precise two collision event occur; one for each instance. The instance can react to this collision event. To this end, from the menu select the object with which you want to define the collision event. Next you place the actions here.

There is a difference in what happens when the instance collides with a solid object or a non-solid object. First of all, when there are no actions in the collision event, nothing happens. The current instance simply keeps on moving; even when the other object is solid. When the collision event contains actions the following happens:

When the other object is solid, the instance is placed back at its previous place (before the collision occurs). Then the event is executed. Finally, the instance is moved to its new position. So if the event e.g. reverses the direction of motion, the instance bounces against the wall without stopping. If there is still a collision, the instance is kept at its previous place. So it effectively stops moving.

When the other object is not solid, the instance is not put back. The event is simply executed with the instance at its current position. Also, there is no second check for a collision. If you think about it, this is the logical thing that should happen. Because the object is not solid, we can simply move over it. The event notifies us that this is happening.

There are many uses for the collision event. Instances can use it to bounce against walls. You can use it to destroy objects when, for example, they are hit by a bullet.

Keyboard events
When the player presses a key, a keyboard event happens for all instances of all objects. There is a different event for each key. In the menu you can pick the key for which you want to define the keyboard event and next drag actions there. Clearly, only a few objects need events for only a few keys. You get an event in every step as long as the player keeps the key depressed. There are two special keyboard events. One is called <No key>. This event happens in each step when no key is pressed. The second one is called <Any key> and happens whatever key is pressed. When the player presses multiple keys, the events for all the keys pressed happen. Note that the keys on the numeric keypad only produce the corresponding events when <NumLock> is pressed.

Mouse events
A mouse event happens for an instance whenever the mouse cursor lies inside the sprite representing the instance. Depending on which mouse buttons are pressed you get the no button, left button, right button, or middle button event. The mouse button events are generated in each step as long as the player keeps the mouse button pressed. The press events are only generated once when the button is pressed. The release events are only generated when the button is released. Note that these events only occur when the mouse is above the instance. If you want to react to mouse press or release events at an arbitrary place, use the global mouse events that can be found in a submenu. There are two special mouse events. The mouse enter event happens when the mouse enters the instance. The mouse leave event happens when the mouse leaves the instance. These events are typically used to change the image or play some sound. Mouse wheel up and mouse wheel down events happen when the user moves the mouse wheel. Finally there are a number of events related to the joystick. You can indicate actions for the four main directions of the joystick (in a diagonal direction both events happen). Also you can define actions for up to 8 joystick buttons. You can do this both for the primary joystick and the secondary joystick.

Other events
There are a number of other events that can be useful in certain games. They are found in this menu. The following events can be found here:

• Outside: This event happens when the instance lies completely outside the room. This is typically a good moment to destroy it.
• Boundary: This event happens when the instance intersects the boundary of the room, that is, it lies (at least) partially outside the room.
• Views: Here you find a number of events that are useful when you use views in your rooms. These events test whether the instance lies completely outside a particular view or interesects the view boundary.
• Game start: This event happens for all instances in the first room when the game starts. It happens before the room start event (see below) but after the creation events for the instances in the room. This event is typically defined in only one "controller" object and is used to start some background music and to initialize some variables, or load some data.
• Game end: The event happens to all instances when the game ends. Again typically just one object defines this event. It is for example used to store certain data in a file.
• Room start: This event happens for all instances initially in a room when the room starts. It happens after the creation events.
• Room end: This event happens to all existing instances when the room ends.
• No more lives: Game Maker has a built-in lives system. There is an action to set and change the number of lives. Whenever the number of lives becomes less than or equal to 0, this event happens. It is typically used to end or restart the game.
• No more health: Game Maker has a built-in health system. There is an action to set and change the health. Whenever the health becomes less than or equal to 0, this event happens. It is typically used to reduce the number of lives or to restart the game.
• End of animation: As indicated above, an animation consists of a number of images that are shown one after the other. After the last one is shown we start again with the first one. The event happens at precisely that moment. As an example, this can be used to change the animation, or destroy the instance.
• End of path: This event happens when the instance follows a path and the end of the path is reached.
• Close button: This event happens when the user clicks on the close button of the window. This only happens when disabling in the game settings the option to have the close button behave as the Escape key.
• User defined: There are 16 of these events. They normally never happen unless you yourself call them from a piece of code.

Drawing event
Instances, when visible, draw their sprite in each step on the screen. When you specify actions in the drawing event, the sprite is not drawn, but these actions are executed instead. This can be used to draw something other than the sprite, or first make some changes to sprite parameters. There are a number of drawing actions that are especially meant for use in the drawing event. Note that the drawing event is only executed when the object is visible. Also note that, independent of what you draw, collision events are based on the sprite that is associated with the instance.

Key press events
This event is similar to the keyboard event but it happens only once when the key is pressed, rather than continuously. This is useful when you want an action to happen only once.

Key release events
This event is similar to the keyboard event but it happens only once when the key is released, rather than continuously.

In some situation it is important to understand the order in which Game Maker processes the events. This is as follows:

• Begin step events
• Alarm events
• Keyboard, Key press, and Key release events
• Mouse events
• Normal step events
• (now all instances are set to their new positions)
• Collision events
• End step events
• Drawing events

The creation, destroy, and other events are performed when the corresponding things happen.

Actions

Actions indicate the things that happen in a game created with Game Maker. Actions are placed in events of objects. Whenever the event takes place these actions are performed, resulting in certain behavior for the instances of the object. There are a large number of different actions available and it is important that you understand what they do. In this chapter I will describe the actions available in simple mode. Note that a number of these actions are only available in the Pro Edition of Game Maker. This will be indicated.

All the actions are found in the tabbed pages at the right of the object property form. There are six sets of actions. You select the set you want by clicking on the correct tab. When you hold you mouse above one of the actions, a short description is shown to remind you of its function.

Let us briefly repeat: To put an action in an event, just drag it from the tabbed pages to the action list. You can change the order in the list, again using dragging. Holding the <Alt> key while dragging makes a copy of the action. (You can drag and copy actions between the lists in different object property forms.) Use the right mouse button and select the correct menu item to remove actions (or use the <Del> key) and to copy and paste selected actions.

When you drop an action in the action list, a window will pop-up most of the time, in which you can fill in certain parameters for the action. The parameters will be described below when describing the actions. Two types of parameters appear in many actions so we will describe these here. At the top you can indicate to which instance the action applies. The default is self, which is the instance for which the action is performed. Most of the time, this is what you want. In the case of a collision event, you can also specify to apply the action to the other instance involved in the collision. For instance, in this way you can destroy the other instance. Finally, you can choose to apply the action to all instances of a particular object. In this way you could change all red balls into blue balls. The second type of parameter is the box labeled Relative. By checking this box, the values you type in are relative to the current values. For example, in this way you can add something to the current score, rather than changing the current score to the new value. The other parameters will be described below. You can later change the parameters by double clicking on the action.

Move actions

The first set of actions consists of those related to movement of objects. The following actions exist:

Move Fixed
Use this action to start the instance moving in a particular direction. You can indicate the direction using the buttons with the arrows on it. Use the middle button to stop the motion. Also you need to specify the speed of the motion. This speed is given in pixels per step. The default value is 8. Preferably don't use negative speeds. You can specify multiple directions. In this case a random choice is made. In this way you can let a monster start moving either left or right.

Move Free
This is the second way to specify a motion. Here you can indicate a precise direction. This is an angle between 0 and 360 degrees. 0 means to the right. The direction is counter-clockwise. So for example 90 indicates an upward direction. If you want an arbitrary direction, you can type random(360). As you will see below the function random gives a random number smaller than the indicated value. As you might have noticed there is a checkbox labeled Relative. If you check this, the new motion is added to the previous one. For example, if the instance is moving upwards and you add some motion to the left, the new motion will be upwards to the left.

Move Towards
This action gives a third way to specify a motion. You indicate a position and a speed and the instance starts moving with the speed towards the position. (It won't stop at the position!) For example, if you want a bullet to fly towards the position of the spaceship you can use as position spaceship.x, spaceship.y. (You will learn more about the use of variables like these below.) If you check the Relative box, you specify the position relative to the current position of the instance. (The speed is not taken relatively!)

Speed Horizontal
The speed of an instance consists of a horizontal part and a vertical part. With this action you can change the horizontal speed. A positive horizontal speed means a motion to the right. A negative one means a motion to the left. The vertical speed will remain the same. Use relative to increase the horizontal speed (or decrease it by providing a negative number).

Speed Vertical
In a similar way, with this action you can change the vertical speed of the instance.

Set Gravity
With this action you can create gravity for this particular object. You specify a direction (angle between 0 and 360 degrees) and a speed, and in each step this amount of speed in the given direction is added to the current motion of the object instance. Normally you need a very small speed increment (like 0.01). Typically you want a downward direction (270 degrees). If you check the Relative box you increase the gravity speed and direction. Note that, contrary to real life, different object can have different gravity directions.

Reverse Horizontal
With this action you reverse the horizontal motion of the instance. This can for example be used when the object collides with a vertical wall.

Reverse Vertical
With this action you reverse the vertical motion of the instance. This can for example be used when the object collides with a horizontal wall.

Set Friction
Friction slows down the instances when they move. You specify the amount of friction. In each step this amount is subtracted from the speed until the speed becomes 0. Normally you want a very small number here (like 0.01).

Jump to Position
Using this action you can place the instance in a particular position. You simply specify the x- and y-coordinate, and the instance is placed with its reference point on that position. If you check the Relative box, the position is relative to the current position of the instance. This action is often used to continuously move an instance. In each step we increment the position a bit.

Jump to Start
This action places the instance back at the position where it was created.

Jump to Random
This action moves the instance to a random position in the room. Only positions are chosen where the instance does not intersect any solid instance. You can specify the snapping used. If you specify positive values, the coordinates chosen with be integer multiples of the indicated values. This could for example be used to keep the instance aligned with the cells in your game (if any). You can specify a separate horizontal snapping and vertical snapping.

Align to Grid
With this action you can round the position of the instance to a grid. You can indicate both the horizontal and vertical snapping value (that is, the size of the cells of the grid). This can be very useful to make sure that instances stay on a grid.

Wrap Screen
With this action you can let an instance wrap around, that is, when it leaves on one side of the room it reappears at the other side. This action is normally used in the Outside event. Note that the instance must have a speed for wrapping to work, cause the direction of wrapping is based on the direction of the motion. You can indicate whether to wrap only horizontal, only vertical, or in both directions.

Move to Contact
With this action you can move the instance in a given direction until a contact position with an object is reached. If there already is a collision at the current position the instance is not moved. Otherwise, the instance is placed just before a collision occurs. You can specify the direction but also a maximal distance to move. For example, when the instance is falling you can move a maximal distance down until an object is encountered. You can also indicate whether to consider solid object only or all objects. You typically put this action in the collision event to make sure that the instance stops in contact with the other instance involved in the collision.

Bounce
When you put this action in the collision event with some object, the instance bounces back from this object in a natural way. If you set the parameter precise to false, only horizontal and vertical walls are treated correctly. When you set precise to true also slanted (and even curved) walls are treated correctly. This is though slower. Also you can indicate whether to bounce only against solid objects or against all objects. Please realize that the bounce is not completely accurate because this depends on many properties. But in many situations the effect is good enough.

Main actions, set 1

The following set of actions deals with creating, changing, and destroying instances of objects, with sounds, and with rooms.

Create Instance
With this action you can create an instance of an object. You specify which object to create and the position for the new instance. If you check the Relative box, the position is relative to the position of the current instance. Creating instances during the game is extremely useful. A space ship can create bullets; a bomb can create an explosion, etc. In many games you will have some controller object that from time to time creates monsters or other objects. For the newly created instance the creation event is executed.

Create Moving
This action works the same as the action above but with two additional fields. You can now also specify the speed and direction of the newly created instance. Note that if you check the Relative box, only the position is relative, not the speed and direction. For example, to make a bullet move in the direction of the person shooting you have to use a little trick. As position use 0,0 and check Relative. As direction we need the current direction of the instance. This can be obtained by typing in the word direction. (This actually is a variable that always indicates the current direction in which the instance is moving.)

Create Random
This action lets you create an instance of one out of four objects. You specify the four objects and the position. An instance of one of these four objects is created at the given position. If you check the Relative box, the position is relative to the position of the current instance. If you need a choice out of less than four objects you can use No Object for some of them. This is for example useful to generate a random enemy at a location.

Change Instance
With this action you can change the current instance into an instance of another object. So for example, you can change an instance of a bomb into an explosion. All settings, such as the motion and the value of variables, will stay the same. You can indicate whether or not to perform the destroy event for the current object and the creation event for the new object.

Destroy Instance
With this action you destroy the current instance. The destroy event for the instance is executed.

Destroy at Position
With this action you destroy all instances whose bounding box contains a given position. This is useful, for example, when you use an exploding bomb. When you check the Relative box the position is taken relative to the position of the current instance.

Change Sprite
Use this action to change the sprite for the instance. You indicate which new sprite. You can also indicate with subimage must be shown. Normally you would use 0 for this (the first subimage) unless you want to see a particular subimage. Use -1 if you do not want to change the current subimage shown. Finally you change the speed of the animation of the subimages. If you only want to see a particular subimage, set the speed to 0. If the speed is larger than one subimages will be skipped. If it is smaller than 1 subimages will be shown multiple times. Don't use a negative speed. Changing sprites is an important feature. For example, often you want to change the sprite of a character depending on the direction in which it walks. This can be achieved by making different sprites for each of the (four) directions. Within the keyboard events for the arrow keys you set the direction of motion and the sprite.

Transform Sprite
Use this action to change the size and orientation of the sprite for the instance. Use the scale factors to make it larger or smaller. The angle gives the counter-clockwise orientation of the sprite. For example, to make the sprite oriented in the direction of motion use as a value direction. For example, this is useful for a car. You can also indicate whether the sprite should be mirrored horizontally and/or flipped vertically. This action is only available in the Pro Edition.

SColor Sprite
Normally the sprite is drawn as it is defined. Using this action you can change the color of the sprite. This color is blended with the sprite, that is, it is combined with the colors of the sprite. If you want to draw a sprite in different colors you better define the sprite in black and white and use the blend color to set the actual color. You can also indicate an alpha transparency. With a value of 1 the sprite is opaque. With a value of 0 it is completely transparent. With a value in between you will partially see the background shine through it. This is great for making explosions. This action is only available in the Pro Edition.

Play Sound
With this action you play one of the sound resources you added to your game. You can select the sound you want to play and choose whether it should play only once (the default) or loop continuously. Multiple wave sounds can play at once but only one midi sound can play at a time. So if you start a midi sound, the current midi sound is stopped.

Stop Sound
This action stops the indicated sound. If multiple instances of this sound are playing all are stopped.

Check Sound
If the indicated sound is playing the next action is performed. Otherwise it is skipped. You can select Not to indicate that the next action should be performed if the indicated sound is not playing. For example, you can check whether some background music is playing and, if not, start some new background music. Note that this action returns true when the sound actually plays through the speakers. After you call the action to play a sound it does not immediately reach the speakers so the action might still return false for a while. Similar, when the sound is stopped you still hear it for a while (e.g. because of echo) and the action will still return true.

Previous Room
Move to the previous room. You can indicate the type of transition effect between the rooms. You should experiment to see what works best for you. If you are in the first room you get an error.

Next Room
Move to the next room. You can indicate the transition.

Restart Room
The current room is restarted. You indicate the transition effect.

Different Room
With this action you can go to a particular room. You indicate the room and the transition effect.

Check Previous
This action tests whether the previous room exists. If so, the next action is executed. You normally need this test before moving to the previous room.

Check Next
This action tests whether the next room exists. If so, the next action is executed. You normally need this test before moving to the next room.

Main actions, set 2

Here are some more main actions, dealing with timing, giving messages to the user, and dealing with the game as a whole.

Set Alarm
With this action you can set one of the twelve alarm clocks for the instance. You select the number of steps and the alarm clock. After the indicated number of steps, the instance will receive the corresponding alarm event. You can also increase or decrease the value by checking the Relative box. If you set the alarm clock to a value less than or equal to 0 you switch it off, so the event is not generated.

Sleep
With this action you can freeze the scene for a particular time. This is typically used at the beginning or end of a level or when you give the player some message. You specify the number of milliseconds to sleep. Also you can indicate whether the screen should first be redrawn to reflect the most recent situation.

Display Message
With this action you can display a message in a dialog box. You simply type in the message. If you use a # symbol in the message text it will be interpreted as a new line character. (Use \# to get the # symbol itself.) If the message text starts with a quote or double quote symbol, it is interpreted as an expression. See below for more information about expressions.

Show Info
With this action you pop up the game information window.

Restart Game
With this action you restart the game from the beginning.

End Game
With this action you end the game.

Save Game
With this action you can save the current game status. You specify the filename for saving (the file is created in the working directory for the game). Later the game can be loaded with the next action. (Please realize that only the basic game status is save. Things that are for example not saved are the current sound that is playing, and advanced aspects like the contents of data structures, particles, etc.)

Load Game
Load the game status from a file. You specify the file name. Make sure the saved game is for the same game and created with the same version of Game Maker. Otherwise an error will occur. (To be precise, the game is loaded at the end of the current step. So some actions after this one are still executed in the current game, not the loaded one!)

Control actions

There are a number of actions with which you can control which other actions are performed. Most of these actions ask a question, for example whether a position is empty. When the answer is yes (true) the next action is executed, otherwise it is skipped. If you want multiple actions to be executed or skipped based on the outcome you can put them in a block by putting start block and end block actions around them. There can also be an else part which is executed when the answer is no. So a question typically looks as follows:

Here the question is asked whether a position for the current instance is collision free. If so, the instance starts moving in a given direction. If not, the instance jumps to a given position.

For all questions there is a field labeled NOT. If you check this field, the result of the question is reversed. That is, if the result was true it becomes false and if it was false, it becomes true. This allows you to perform certain actions when a question is not true.

For many questions you can indicate that they should apply to all instances of a particular object. In this case the result is true only if it is true for all instances of the object. For example, you can check whether for all balls the position slightly to the right is collision free.

The following questions and related actions are available. (Note that they all have a differently shaped icon and a different background color so that they can more easily be distinguished from other actions.)

Check Empty
This question returns true if the current instance, placed at the indicated position does not generate a collision with an object. You can specify the position as either absolute or relative. You can also indicate whether only solid, or all objects, should be taken into account. This action is typically used to check whether the instance can move to a particular position.

Check Collision
This is the reverse of the previous action. It returns true if there is a collision when the current instance is placed at the given position (again, either only with solid objects or with all objects).

Check Object
This question returns true if the instance placed at the indicate position meets an instance of the indicated object.

Test Instance Count
You specify an object and a number. If the current number of instances of the object is equal to the number the question returns true. Otherwise it returns false. You can also indicate that the check should be whether the number of instances is smaller than the given value or larger than the given value. This is typically used to check whether all instances of a particular type are gone. This is often the moment to end a level or a game.

Test Chance
You specify the number of sides of a dice which is then thrown. Then if the dice lands on one, the result is true and the next action is performed. This can be used to put an element of randomness in your game. For example, in each step you can generate with a particular chance a bomb or a change of direction. The larger the number of sides of the dice, the smaller the chance. You can actually use real numbers. For example if you set the number of sides to 1.5 the next action is performed two out of three times. Using a number smaller than 1 makes no sense.

Check Question
You specify a question. A dialog is shown to the player with a yes and a no button. The result is true is the player answers yes.

Test Expression
This is the most general question action. You can enter an arbitrary expression. If the expression evaluates to true (that is, a number larger or equal to 0.5) the next action is performed. See below for more information on expressions.

Check Mouse
Returns true if the indicated mouse button is pressed. A standard use is in the step event. You can check whether a mouse button is pressed and, if so, for example move to that position (use the jump to a point action with values mouse_x and mouse_y).

Check Grid
Returns true if the position of the instance lies on a grid. You specify the horizontal and vertical spacing of the grid. This is very useful when certain actions, like making a turn, are only a llowed when the instance is on a grid position.

Start Block
Indicates the start of a block of actions.

End Block
Indicates the end of a block of actions.

Else
Behind this action the else part follows, that is executed when the result of the question is false.

Repeat
This action is used to repeat the next action (or block of actions) a number of times. You simply indicate the number.

Exit Event
When this action is encountered no further actions in this event are executed. This is typically used after a question. For example, when a position is free nothing needs to be done so we exit the event. In this example, the following actions are only executed when there is a collision.

If you want more control over what is happening in the game you can use the built-in programming language that is described on part 4 of the documentation. If gives you much more flexibility than using the action. Simpler use but also important involves the use of your own variables. The following actions deal with this.

Execute Code
When you add this action, a form shows in which you can type in a piece of code which must be execute. This can contain simple function calls or more complex code. Use the code action peferably only for small pieces of code. For longer pieces you are strongly advised to use scripts which are described in part 2 of the documentation.

Comment
Use this action to add a line of comment to the action list. The line is shown in italic font. Adding comments helps you remember what your events are doing. The action does not do anything. But realize that it still is an action. So when you place it after a conditional action it is the action that is executed if the condition is true (even though it does not do anything).

Set Variable
There are many built-in variables in the game. With this action you can change these. Also you can create your own variables and assign values to them. You specify the name of the variable and the new value. When you check the Relative box, the value is added to the current value of the variable. Please note that this can only be done if the variable already has a value assigned to it! See below for more information about variables.

Test Variable
With this action you can check what the value of a particular variable is. If the value of the variable is equal to the number provided, the question returns true. Otherwise it returns false. You can also indicate that the check should be whether the value is smaller than the given value or larger than the given value. See below for more information about variables. Actually, you can use this action also to compare two expressions.

Draw Variable
With this action you can draw the value of a variable at a particular position on the screen. Note that this can only be used in the draw event of an object.

Score actions

In most games the player will have a certain score. Also many games give the player a number of lives. Finally, often the player has a certain health. The following actions make it easy to deal with the score, lives, and health of the player.

Set Score
Game Maker has a built-in score mechanism. The score is normally displayed in the window caption. You can use this action to change the score. You simply provide the new value for the score. Often you want to add something to the score. In this case don't forget the check the Relative box.

Test Score
With this question action you can check whether the score has reached a particular value. You indicate the value and whether the score should be equal to that value, be smaller than the value or be larger than the value.

Draw Score
With this action you can draw the value of the score at a particular position on the screen. You provide the positions and the caption that must be placed in front of the score. The score is drawn in the current font. This action can only be used in the drawing event of an object.

Show Highscore
For each game the top ten scores are maintained. This action displays the highscore list. If the current score is among the top ten, the new score is inserted and the player can type his or her name. You can indicate what background image to use, whether the window should have a border, what the color for the new entry and the other entries must be, and which font to use.

Clear Highscore
This action clears the highscore table.

Set Lives
Game Maker also has a built-in lives system. With this action you can change the number of lives left. Normally you set it to some value like 3 at the beginning of the game and then decrease or increase the number depending on what happens. Don't forget to check the Relative box if you want to add or subtract from the number of lives. At the moment the number of lives becomes 0 (or smaller than 0) a "no more lives" event is generated.

Test Lives
With this question action you can check whether the number of lives has reached a particular value. You indicate the value and whether the number of lives should be equal to that value, be smaller than the value or be larger than the value.

Draw Lives
With this action you can draw the number of lives at a particular position on the screen. You provide the positions and the caption that must be placed in front of the number of lives. The number of lives is drawn in the current font. This action can only be used in the drawing event of an object.

Draw Life Images
Rather than drawing the number of lives left as a number, it is often nicer to use a number of small images for this. This action does precisely that. You specify the position and the image and at the indicated position the number of lives is drawn as images. This action can only be used in the drawing event of an object.

Set Health
Game Maker has a built-in health mechanism. You can use this action to change the health. A value of 100 is considered full health and 0 is no health at all. You simply provide the new value for the health. Often you want to subtract something from the health. In this case don't forget the check the Relative box. When the health becomes smaller or equal to 0 an out of health event is generated.

Test Health
With this question action you can check whether the health has reached a particular value. You indicate the value and whether the health should be equal to that value, be smaller than the value or be larger than the value.

Draw Health
With this action you can draw the health in the form of a health bar. When the health is 100 the full bar is drawn. When it is 0 the bar is empty. You indicate the position and size of the health bar and the color of the bar and the background.

Score Caption
Normally in the window caption the name of the room and the score is displayed. With this action you can change this. You can indicate whether or not to show the score, lives, and/or health and what the caption for each of these must be.

Drawing actions

Normally in each step of the game, for each instance, its sprite is drawn in the room. You can change this by putting actions in the draw event. (Note that these are only executed when the instance is visible!) The following drawing actions are available. These actions only make sense in the drawing event. At other places they are basically ignored.

Draw Sprite
You specify the sprite, the position (either absolute or relative to the current instance position) and the subimage of the sprite. (The subimages are numbered from 0 upwards.) If you want to draw the current subimage, use number -1.

Draw Background
You indicate the background image, the position (absolute or relative) and whether the image should be tiled all over the room or not.

Draw Text
You specify the text and the position. A # symbol in the text is interpreted as going to a new line. (Use \# to get the # symbol itself.) So you can create multi-line texts. If the text starts with a quote or a double quote, it is interpreted as an expression. For example, you can use

'X: ' + string(x)

to display the value of the x-coordinate of the instance. (The variable x stores the current x-coordinate. The function string() turns this number into a string. + combines the two strings.)

Draw Scaled Text
This action is similar to the previous action but this time you can also specify a horizontal and vertical scaling factor to change the size of the text and you can specify an angle to rotate it. This action is only available in the Pro Edition.

Draw Rectangle
You specify the coordinates of the two opposite corners of the rectangle; either absolute or relative to the current instance position.

Horizontal Gradient
This action also draws a rectangle but this time using a gradient color that changes from left to right. You specify the rectangle and the two colors to use. This action is only available in the Pro Edition.

Vertical Gradient
This action also draws a rectangle but this time using a gradient color that changes from top to bottom. You specify the rectangle and the two colors to use. This action is only available in the Pro Edition.

Draw Ellipse
This action draws an ellipse. You specify the coordinates of the two opposite corners of the surrounding rectangle; either absolute or relative to the current instance position.

Gradient Ellipse
Again an ellipse is drawn but this time you specify a color for the center and the boundary. This action is only available in the Pro Edition.

Draw Line
You specify the coordinates of the two endpoints of the line; either absolute or relative to the current instance position.

Draw Arrow
Draws an arrow. You specify the coordinates of the two endpoints of the line and the size of the arrow tip.

Set Color
Lets you set the color used for drawing shapes, lines, and text. (It does not influence the way sprites and backgrounds are drawn.)

Set Full Screen
With this action you can change the screen mode from windowed to fullscreen and back. You can indicate whether to toggle the mode or whether to go to windowed or fullscreen mode.

Take Snapshot
With this action you can take a snapshot image of the game and store it in a .bmp file. You specify the filename to store the image in. This action is only available in the Pro Edition.

Create Effect
With this action you can create all sorts of effects in a very simple way. You specify the type of effect, e.g. an explosion or smoke, its position, its size and its color and whether it should be shown below the objects or on top of them. For the rest it works automatic. (For rain and snow the position is irrelevant as it always falls down from the top of the screen. To get continuous rain you should create it in each step.) This action is only available in the Pro Edition.

Using expressions and variables

In many actions you need to provide values for parameters. Rather than just typing a number, you can also type a formula, e.g. 32*12. But you can actually type much more complicated expressions. For example, if you want to double the horizontal speed, you could set it to 2*hspeed. Here hspeed is a variable indicating the current horizontal speed of the instance. There are a large number of other variables that you can use. Some of the most important ones are:

x the x-coordinate of the instance
y the y-coordinate of the instance
hspeed the horizontal speed (in pixels per step)
vspeed the vertical speed (in pixels per step)
direction the current direction of motion in degrees (0-360)
speed the current speed in this direction
visible whether the object is visible (1) or invisible (0)
image_index this variable indicate which subimage in the current sprite is currently shown. If you change it and set the speed to 0 (see below) you can display a fixed subimage.
image_speed this variable indicates the speed with which the subimages are shown. The default value is 1. If you make this value larger than 1 some subimages are skipped to make the animation faster. If you make it smaller than 1 the animation becomes slower by repeating subimages.
score the current value of the score
lives the current number of lives
health the current health (0-100)
mouse_x x-position of the mouse
mouse_y y-position of the mouse

You can change most of these variables using the set variable action. You can also define your own variables by setting them to a value. (Don't use relative, because they don't exist yet.) Then you can use these variables in expressions. Variables you create are local to the current instance. That is, each object has its own copy of them. To create a global variable, put the word global and a dot in front of it.

You can also refer to the values of variables for other objects by putting the object name and a dot in front of them. So for example, if you want a ball to move to the place where the coin is you can set the position to (coin.x , coin.y). In the case of a collision event you can refer to the x-coordinate of the other object as other.x. In conditional expressions you can use comparisons like < (smaller than), >, etc.

In your expressions you can also use functions. For example, the function random(10) gives a random real number below 10. So you can set for example the speed or direction of motion to a random value. Many more functions exist. They are described in part 4 of the documentation.

Creating rooms

Now that you have defined the objects with their behavior in the form of events and actions, it is time to create the rooms or levels in which the game takes place. Any game will need at least one room. In these rooms we place instances of the objects. Once the game starts the first room is shown and the instances in it come to life because of the actions in their creation events.

There are a large number of possibilities when creating rooms. Besides setting a number of properties and adding the instances of the objects you can add backgrounds, define views, and add tiles. Most of these options are discussed later. In this chapter we will only discuss some basic settings, the addition of instances of objects, and the setting of background images.

To create a room, choose Create Room from the Resources menu. The following form will appear:

At the top of the form there is a tool bar. On this you can indicate the size of the grid cells used for aligning objects. Also you can indicate whether or not to show the grid lines and whether or not to show the backgrounds, etc. It is sometimes useful to temporarily hide certain aspects of the room. Realize though that when you are adding instances of objects, these will always be shown, independent of the view setting.) There are also buttons to clear all instances from the room and to shift all instances over a number of pixels. Use negative numbers to shift them left or up. This is useful when for instance you decided to enlarge the room. (You can also use this to place instances outside the room, which is sometimes useful.). Finally there is the Undo button to undo the last change to the room and the OK button to save the changes. (Click on the cross at the top right to close the form without saving the changes.)

At the left you will see three tab pages (five in advanced mode). The objects tab is where you add instances of objects to the room. In the settings tab you can indicate a number of settings for the room. In the backgrounds tab you can set background images for the room.

Adding instances

At the right in the room design form you see the room. At the start it is empty, with a gray background.

To add instances to the room, first select the objects tab if this one is not already visible. Next select the object you want to add by clicking on the button with the menu icon (or by clicking in the image area at the left). The image of the object appears at the left. (Note that when you changed the origin of the sprite there is a cross in the image. This indicates how the instances will be aligned with the grid.) Now click with your left mouse button in the room area at the right. An instance of the object appears. It will snap to the indicated grid. If you hold the <Alt> key while placing the instance it is not aligned to the grid. If you hold down the mouse button while dragging it over the room, you move the instance to the correct place. If you hold the <Shift> key while pressing and moving the mouse multiple instances are added. With the right mouse button you can remove instances. In this way you define the contents of the room.

As you will notice, if you place an instance on top of another one, the original instance disappears. Normally this is what you want, but not always. This can be avoided by unchecking the box labeled Delete underlying at the left.

If you want to change the position of an instance, hold the <Ctrl> key and click with the left mouse button on the instance and hold down the button. You can now drag it to a new position. (Use <Alt> for precise positioning.)

If you hold the <Ctrl> key while clicking with the right mouse button on an instance, a menu appears. Here you can delete the object, type in a precise position for the instance, or move the bottommost instance at the position to the top or send the topmost instance to the bottom.

Room setting

Each room has a number of settings that you can change by clicking on the settings tab.

Each room has a name. Best give it a meaningful name. There also is a caption. This caption is displayed in the window caption when the game is running. You can set the width and height of the room (in pixels). Also you can set the speed of the game. This is the number of steps per second. The higher the speed, the smoother the motion is. But you will need a faster computer to run it.

Setting the background

With the tab backgrounds you can set the background image for the room. Actually, you can specify multiple backgrounds. The tab page looks as follows:

At the top you will see the background color. You can click on it to change it. The background color is only useful if you don't use a background image that covers the whole room. Otherwise, best uncheck the box labeled Draw background color because this will be a waste of time.

At the top you see a list of 8 backgrounds. You can define each of them but most of the time you will need just one or two. To define a background, first select it in the list. Next check the box labeled Visible when room starts otherwise you won't see it. The name of the background will become bold when it is defined. Now indicate a background image in the menu. There are a number of settings you can change. First of all you can indicate whether the background image should tile the room horizontally and/or vertically. You can also indicate the position of the background in the room (this will also influence the tiling). A different option is to stretch the background. The background will then be scaled so that it fills the entire room. The aspect ration of the image will not be maintained. Finally you can make the background scrolling by giving it a horizontal or vertical speed (pixels per step). Better not use scrolling with a stretched background. The result will be a bit jaggy.

There is one more checkbox labeled Foreground image. When you check this box, the background is actually a foreground, which is drawn on top of everything else rather than behind it. Clearly such an image should be partially transparent to be of any use.

Distributing your game

With the information in the preceding chapters you can create your games. When your game is finished you obviously want other people to play it. You can of course give them the .gmk file that you created and let them use Game Maker to play it but this is normally not what you want. First of all, you don't want others to be able to change the game, and secondly you also want people to play the game even if they do not have Game Maker. So you would like to create a stand-alone executable of your game.

Creating stand-alone executables is very easy in Game Maker. In the File menu you select the item Create Executable. You will be asked for the name of the executable that should contain the game. Indicate a name, press OK and you have your stand-alone game that you can give to anyone you like. You can change the icon for the stand-alone game in the Global Game Settings.

Once you have created a stand-alone executable in the way described above you can give this file to other people or place it on your website to download. You are free to distribute the games you create with Game Maker in any way you like. You can even sell them. This of course assumes that the sprites, images, and sounds you use can be distributed or sold as well. See the enclosed license agreement for more information.

It is normally useful to zip your executable, together with some readme information. In Windows XP this can be done directly through the right mouse button menu, and there are many free zip utilities available on the web. Alternatively you can create an installer for your game. Again, a large number of free installation creation programs are available on the web.

Advanced use

This section of the help file gives you information about the more advanced aspects of Game Maker.

Advanced mode

Up to now we have considered the simple features of Game Maker. But there are a lot more possibilities. To be able to use these you must run Game Maker in advanced mode. This is easy to change. In the File menu, click on the menu item Advanced mode. (To fully see the effects you should restart Game Maker or at least save your game and load it anew.)

When you start Game Maker in advanced mode, the following form is shown:

It contains all that was there in simple mode, but there are a number of additional resources, buttons, and menu items. Also, as we will see in the chapters that follow, the different resources have additional options. Here we will discuss the additional menu items.

File menu

In the file menu you can find the following additional commands:

• Publish your Game. This command will take you to our website were you can easily upload and publish your finished game such that everybody can play it. Carefully follow the instructions to make your game available. Please only use this for finished games, not for preliminary versions. This possibility is only available in the Pro Edition.
• Merge Game. With this command you can merge all the resources (sprites, sounds, objects, rooms, etc.) from another game into the current game. This is very useful if you want to make parts you want to reuse (e.g. menu systems). (Note that all resources and instances and tiles will get a new id, which might cause problems if you use these in scripts.) It is your responsibility to make sure that the resources in the two files have different names, otherwise problems might occur.
• Preferences. Here you can set a number of preferences about Game Maker. They will be remembered between different calls of Game Maker. See below for a list of all possibilities.

Preferences

Under the Preferences menu item in the File menu you can set a number of preferences that will be maintained between runs of Game Maker. The following preferences can be set:

• Show recently edited games in the file menu. If checked the eight most recently edited games are shown under the recent files in the file menu.
• Load last opened file on startup. If checked when you start Game Maker the most recently opened file is opened automatically.
• Keep backup copies of files. If checked the program saves a backup copy of your game with the extension gb0-gb9. You can open these games in Game Maker. You are strongly advised to use at least one backup copy for your work!
• Maximal number of backups. Here you can indicate how many (1-9) different backup copies should be remembered by the program.
• Show progress while loading and saving files. If checked, when load or save a file a progress indicator is shown.
• At startup check for, and remove old temporary files. Game Maker and games created with it, create temporary files. Normally these are automatically removed but sometimes, for example when games crash, they are left behind. If this option is checked, Game Maker checks whether such files exist and removes them at startup.
• Don't show the website in the main window. When checked the image and link to the website on the main window are not shown.
• Hide the designer and wait while the game is running. When checked the game making program is hidden while you are testing a game.
• Run games in secure mode. If checked, any game created with Game Maker that runs on your machine will not be allowed to execute external programs or change or delete files at a place different from the game location. (This is a safeguard against Trojan horses although success is not guaranteed.) Checking this means that games that utilizes external files etc. won't be running correctly. The setting only works while Game Maker is running. So if you run the game independently of Game Maker, for example as an executable stand-alone, it is NOT run in secure mode.
• Show the origin and bounding box in the sprite image. If checked, in the sprite properties form, in the sprite image, the origin and bounding box for the sprite are indicated.
• In object properties, show hints for actions. If checked, in the object properties form, when you hold your mouse over one of the actions, a description is shown.
• When closing, remove instances outside the room. If checked, the program warns you when there are instances or tiles outside a room and lets you remove them.
• Remember room settings when closing the form. If checked, a number of room settings, like whether to show the grid, whether to delete underlying objects, etc. are remembered when you edit the same room later.
• Scripts and code and colors. See the chapter on scripts for more information about these preferences.
• Image editor. Default Game Maker uses a built-in editor for images. If you favor a different image editing program you can specify here to use that different program for editing the images.
• External sound editors. You can indicate here which external editors to use for the different sound types. (Note that Game Maker does not have a built-in sound editor so if you don't specify editors here you cannot edit the sounds.)

Edit menu

In the edit menu you can find the following additional commands:

• Add group. Resources can be grouped together. This is very useful when you make large games. For example, you can put all sounds related to a certain object in a group, or you can group all objects that are used in a particular level. This command creates a new group in the currently selected resource type. You will be asked for a name. Groups can again contain groups, etc. As indicated below you can drag resources into the groups.
• Find Resource. With this command you type in the name of a resource and open the corresponding property form.
• Expand Resource Tree. Fully expands the resource tree, showing all resources.
• Collapse Resource Tree. Fully collapses the resource tree, hiding all resources.
• Show Object Information. Using this command you can get an overview of all objects in the game.

Resources menu

In this menu you can now also create the additional resources. Note that for each of them there is also a button on the toolbar and a keyboard shortcut.

Scripts menu

In the scripts menu you can find the following additional commands:

• Import Scripts. Can be used to import useful scripts from files.
• Export Scripts. Can be used to save your scripts in a file, to be used by others. When you select a script resource only this script is saved. When you select a group all scripts in the group are saved. W