Physics and Collision

FlixelGDX makes collision detection simple. Flixel.collide(a, b) checks for overlap between any two objects, groups, or combinations and applies simple arcade physics (separation) to resolve them. Flixel.overlap(a, b) reports the overlap without moving anything — useful for trigger zones and pickups. Pass a notify callback to react to each overlapping pair; the optional fourth argument is a process callback that decides whether a pair counts as overlapping (pass null for plain AABB overlap).

Java

private int score = 0;

// Allocate the callback once so a new lambda isn't created every frame!
private BiConsumer<FlixelObject, FlixelObject> notifyCallback = (_, coin) -> {
  score++;
  coin.destroy();
};

@Override
public void update(float elapsed) {
  super.update(elapsed);

  // Solid collision: player bounces off walls.
  Flixel.collide(player, walls);

  // Trigger: collect a coin without physics response.
  Flixel.overlap(player, coins, notifyCallback, null);
}

Kotlin

private val score = 0

// Allocate the callback once so a new lambda isn't created every frame!
private val notifyCallback = { _: FlixelObject, coin: FlixelObject ->
  score++
  coin.destroy()
}

override fun update(elapsed: Float) {
  super.update(elapsed)

  // Solid collision: player bounces off walls.
  Flixel.collide(player, walls)

  // Trigger: collect a coin without physics response.
  Flixel.overlap(player, coins, notifyCallback, null)
}

Key physics properties on FlixelObject (accessed through getters and setters):

Property	What it does
setVelocity(x, y)	Current movement speed (pixels per second).
setAcceleration(x, y)	Per-frame velocity change (gravity, friction ramps).
setDrag(x, y)	Friction-like deceleration applied when no acceleration is active.
setMaxVelocity(x, y)	Caps how fast the object can move.
setImmovable(true)	Makes the object a solid wall that does not move on collision.

Calling setImmovable(true) on your tilemap or wall group turns it into a one-sided solid surface that player objects will bounce off of, without requiring any custom collision code.