Question: How do you handle collisions in GameMaker Studio?

Answer

Collisions are a fundamental part of many video games, and GameMaker Studio provides various functions to handle them. Here is an overview of how you can manage collisions in GameMaker:

Checking for Collisions

To check if an instance will collide with another object, GameMaker provides several functions such as:

• place_meeting(x, y, object): Returns true if the instance would collide with the specified object at the given position.
• instance_place(x, y, object): Returns the instance id of the first instance found at the position where a collision occurs or noone if there's no collision.

Here's an example of using place_meeting to check for a collision before moving an instance:

if (!place_meeting(x+speed, y, obj_wall)) {
    x += speed;
}

Resolving Collisions

Once a collision is detected, it might be necessary to resolve it by moving the instance out of the colliding position. You could do this manually by adjusting the instance's x and y coordinates, or by using functions like move_contact_solid(direction, maxdist) which moves the instance along the given direction until it is just out of contact with any solid instance or has moved the maximum distance allowed.

Create Event-Based Collision Code

GameMaker also allows you to define event-based collision handling via the Collision Event in an object's Events list. When the object collides with another specified object, the code within that event runs automatically.

Using Masks

Sometimes you may want to have a different collision area than the sprite itself. This can be achieved by using masks. In the sprite properties, you can assign a collision mask which can either be the same as the sprite, a rectangle, an ellipse, or a precise per-pixel collision shape.

Physics Engine

For more complex physics-based collisions, GameMaker Studio has a built-in physics engine that you can enable for your project. This allows for realistic simulation of gravity, friction, and collisions between instances with physics properties.

Here's an example of setting up a simple physics world and objects:

// Enable the physics in the room
physics_start();

// Set gravity
physics_world_gravity(0, 10);

// Create a physics-based object
instance_create_layer(x, y, "Instances", object);
phy_position_x = x;
phy_position_y = y;
phy_fixed_rotation = true; // Prevents object from rotating

Remember that when using the physics engine, standard collision functions like place_meeting won't work as expected since physics-based collisions are managed differently.

Advanced Techniques

For platformers and other genres requiring pixel-perfect collision detection, developers often employ additional data structures like tilemaps or grids and write custom collision detection and resolution algorithms.

In summary, GameMaker Studio offers a variety of ways to detect and handle collisions that cater to different game types and mechanics. The choice of method will depend on the specific needs of the game being developed.