Understanding GameMaker Events

In GameMaker, an “event” is a specific action or trigger that causes code to execute in a game project. Events are the cornerstone of GameMaker’s event-driven programming model, enabling developers to create games without writing complex code from scratch. Each event is executed on an instance of an object while the game is running, similar to methods in Object-Oriented Programming (OOP).

GameMaker offers various types of events, each serving a distinct purpose:

  • Create Event: Triggered when an instance of an object is created in a room.
  • Step Event: Triggered on every frame update, allowing regular code execution.
  • Collision Event: Triggered when two objects collide.
  • Mouse Event: Triggered by mouse or pointing device interactions.
  • Keyboard Event: Triggered when a key is pressed on the keyboard.

GameMaker Create Event

The “Create Event” is vital in GameMaker, initializing an object with designated values and executing the encapsulated code only once upon the object’s creation. Unlike the “Step Event,” which triggers repeatedly, the “Create Event” occurs a single time. For those familiar with object-oriented programming, this concept will be recognizable.

Understanding GameMaker Coordinates

Before incorporating what we’ve learned into our player object’s movement, it’s crucial to understand GameMaker’s coordinate system.

Rooms & Coordinates

In GameMaker, “rooms” represent the levels or stages of your game, where various objects are placed to create gameplay. Coordinates determine the locations of these objects within a room.

  • Origin (0, 0): The top-left corner of the room is the origin, with x = 0 and y = 0.
  • X-axis: The horizontal axis; increasing the x-coordinate moves objects to the right.
  • Y-axis: The vertical axis; increasing the y-coordinate moves objects downward.
Gamemaker co-ordinates

GameMaker provides built-in variables and functions to manipulate these coordinates:

Built-in Variables for Coordinates

  • x and y: Represent the x and y positions of an instance within the room.
  • room_width and room_height: Represent the width and height of the room in pixels.

GameMaker Functions Related to Coordinates

  • instance_create_layer(x, y, layer_id, object): Creates an instance of an object at the specified x and y coordinates on the given layer.
  • instance_position(x, y, object): Validates the existence of an instance of a given object at certain x and y coordinates.

Practical Application

Here’s an example of positioning an object at defined room coordinates:

// Create an instance of obj_player at x = 100 
//and y = 200 on the "Instances" layer
instance_create_layer(100, 200, "Instances", objPlayer);

Implementing the above code within the Create Event of an object spawns a player object at the specified coordinates. Ensure you correctly reference your player object within the instance_create_layer function.

GameMaker Step Event

To add movement code for our player object, we need to understand the “Step Event.”

A Step Event is a code event that runs every frame of the game. If your game runs at 60 frames per second, this code is executed 60 times per second, enabling fluid game mechanics, particularly for player and enemy movements.

Conclusion

Understanding GameMaker events and coordinates is crucial for game development. Events like Create and Step Events provide control over object behaviors, while the coordinate system helps position and move objects within a room. By mastering these concepts, you can create dynamic and interactive gameplay experiences in GameMaker.

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