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GAMEMAKER


CONTENT

 

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SPRITES

 

A sprite is an image that is used inside a game.  Often, a sequence of sprites is displayed one after another to create the illusion of animation.

 

Sprites are used for characters, bad guys, objects, walls and even backgrounds (sometimes).

 

Here is an image of 82 different sprites used in a Super Mario Brothers game:

 

 

COMPUTER EVENTS

 

In computers, an event is a special type of activity that computer programs watch or listen for.  Here are some examples of events that an application might be watching for:

 

  • a mouse button is clicked anywhere;
  • a mouse is clicked while the cursor is on an object;
  • a keyboard key is pressed;
  • two objects collide;
  • the mouse cursor is moved over an object;
  • a timer runs out.

 

Another type of event is a creation event that runs whenever an object instance is first created.

 

ACTIONS

 

An action is what happens as a response to an event.  This is best explained via examples:

 

If a character gets hit by a rocket and should disappear, then we have:

 

  • Event: A collision event between a character and a weapon.
  • Action: Character is removed from scene

 

If the mouse is clicked on a button that makes a window pop up, then we have:

 

  • Event: A mouse click event
  • Action: A new window is opened with specified data

 

OBJECTS (IN GAME MAKER)

 

In Game Maker, an object is a prototype.  You create a prototype object and then you can use as many instances (copies) of that object in your game. 

 

Note that unfortunately the term object is used in opposite ways in many programming languages.

 

ROOMS

 

In GameMaker, rooms are simply the location inside which all objects interact.  Usually, we use a different room for each level that we do.  Rooms are also used for intro screens and ending screens.

 

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STEPS

 

GameMaker, just like all computer games, separates time into finite sections called steps.  Every second, there are 30 steps that occur.  (This amount can be changed in the settings tab of a room.  However, the higher the steps per second, the more difficulty your CPU will have to keep up with the game.)

 

ALARMS

 

Alarms, also known as alarm clocks, are special devices that are set to a number of steps such as 60.  Then they automatically count down to zero.  Once zero is reached, an alarm event occurs and the corresponding actions are done.

 

By default, GameMaker runs at 30 steps per second.  So we set an

to 60, it will take 2 seconds for it to trigger an alarm event.

 

ALARM EVENTS & ACTIONS

 

Any object can make use of 10 different alarms (from zero to nine). 

 

We place the alarm event code inside the object and add any corresponding actions. 

 

We also need to start the alarm (SET ALARM action).  This is often done in the create event.

 

CONTINUOUS REPETITION

 

We often want to repeat an action every so often.  We do this by resetting the alarm inside the alarm event. 

 

EXAMPLE

 

If we wanted to continuously play a sound every 100 steps, we would do something like this:

 

  • In the creation event of your main character, you set an alarm to a certain number of steps.  The alarm will automatically count down to zero.

  • Still in the main character, you add an event for that alarm.  Inside, you add the action to play the sound.  You also reset the alarm to the number of steps that want before the sound plays again.

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COORDINATES

 

Remember your graph work in math with the x and y axis’s?  Well, you need to know a little about this for Game Maker.  Each pixel in the room window is given a coordinate.  At the very top left, you find (0,0).  Just to the right of that, you find (0,1).

 

To help find the maximum size of the room, there are built in variables to specify that size.  The words room_height and room_width specify the height and width of the room in pixels.

 

So the point (0,room_height) is at the bottom left.

 

The point (room_width, room_height) is at the bottom right.

 

The point (room_width, 0) is at the top right.

 

 

VARIABLES

 

What are they?

 

Variables are what allow us to store data in the computer.  For example, the location of your character is stored in an x variable and a y variable.  Your score is also stored in a variable.  The number of the current level is also stored in a variable.  All data is stored in some sort of variable.

 

Common variables

 

x – inside an object, this refers to the object’s x coordinate inside the room

y – inside an object, this refers to the object’s y coordinate inside the room

 

room_width – the room’s width in pixels

room_height – the room’s height is pixels

 

RANDOM VALUES

 

In computer applications, it is often necessary to generate random values.  In GameMaker, we have a built-in function (or command) called random that we can use.

 

To get a random number between 0 and 500, we use:

 

          random(500)

 

To get a random number between 0 and 10, we use:

 

          random (10)

 

To get a random number between 0 and the room’s width, we use:

 

          random(room_width)

 

IF STATEMENTS

 

What are they?

 

If statements are added in the actions section of an event to check if certain conditions are true.  Based on the result of this check, some actions may be executed or skipped.

 

If statements are how computers make decisions.

 

Example

 

Here are a few examples:

 

          If character’s health is less than 0, then display GAME OVER

 

          If the plane is as far left as it can go, then do not let it move further left

 

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Multiple Rooms

 

Having multiple rooms is very easy.  Simply make more than one room.  At whichever point you want to go to the next room, you simply apply the Next Room action.

 

If you apply this action where there is no next room, the game will crash.  However, there is a way to check if there is another room.

 

Start Screen

 

You can use the first room to place a neat start screen graphic.  Adding an event that listens for any key to be pressed and moving to the next room allows you to easily start the game. 

 

Object Creation

 

Every time you start a new room (or restart a room), the object’s CREATE event is executed.

 

Therefore, setting things like score and lives should be done in an object that does not appear on any of the levels.

 

The best solution is to have a Start screen that has an invisible object that sets this information for you.

 

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