Question: How do you implement top-down movement in GameMaker?

Answer

Implementing top-down movement in GameMaker involves using GameMaker Language (GML) to update the position of a character or object based on player input. Below is an example code snippet that defines simple top-down movement for an object.

1. Create a new object (e.g., obj_player) and add events to handle keyboard input.
2. In the Step event of obj_player, add the following GML script:

var moveSpeed = 4; // Movement speed of the player
var vx = 0; // Horizontal velocity
var vy = 0; // Vertical velocity

// Check for horizontal movement
if (keyboard_check(vk_left)) {
    vx = -moveSpeed;
} else if (keyboard_check(vk_right)) {
    vx = moveSpeed;
} else {
    vx = 0;
}

// Check for vertical movement
if (keyboard_check(vk_up)) {
    vy = -moveSpeed;
} else if (keyboard_check(vk_down)) {
    vy = moveSpeed;
} else {
    vy = 0;
}

// Update the object's position
x += vx;
y += vy;

This script checks for key presses and sets horizontal (vx) and vertical (vy) velocities accordingly. The object's position (x and y) is then updated by these velocities, which moves the object around the room.

For smoother movement and collision handling, consider using functions like lengthdir_x(speed, direction) and lengthdir_y(speed, direction) to calculate velocities and place_meeting(x + vx, y + vy, obj_solid) combined with move_contact_solid(direction, maxdist) to avoid moving into solid objects.

Furthermore, you may want to separate the input detection from the movement logic, especially if your game will grow in complexity. This can be done by storing the input in variables and using those variables in the movement calculations.

Remember that this is just a basic implementation. Depending on the mechanics of your game, you might want to include acceleration, deceleration, and different types of movement such as strafing or dashing.