Use FlxG.overlap() to check if the bounding box of a FlxObject (or any objects in a group) overlaps the bounding box of another FlxObject (or any objects in the same or another group).
FlxG.overlap() will return true if it detects an overlap, and false. if it does not.
// overlaps will be true if the two objects are overlapping each other overlaps = FlxG.overlap(objectA, objectB);
package; import flixel.FlxG; import flixel.FlxSprite; import flixel.FlxState; class PlayState extends FlxState { var sprite:FlxSprite; var box:FlxSprite; override public function create() { super.create(); box = new FlxSprite("assets/bigbox.png"); box.screenCenter(); add(box); sprite = new FlxSprite("assets/sprite.png"); sprite.y = FlxG.height / 2 - sprite.height / 2; sprite.velocity.x = 100; add(sprite); } override public function update(elapsed:Float) { if ((sprite.velocity.x > 0 && sprite.x >= FlxG.width - sprite.width) || (sprite.velocity.x < 0 && sprite.x <= 0)) { sprite.velocity.x *= -1; } box.alpha = FlxG.overlap(sprite, box) ? 0.5 : 1; super.update(elapsed); } }