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Projectiles going through collision objects

October 27, 2022

Ever had the problem where you’re firing a bullet or some kind of projectile at high speeds, and it just goes right through the collision object, instead of hitting it?

Here’s a weapon that fires a bullet at random velocities, to demonstrate the issue:

The bullets impact the character in various places, rather than at the first point of contact. I haven’t found a way to enable any kind of continuous contact option, outside of playing with the safe_margin setting. I ended up adding a raycast:

The ray cast looks somewhat like this:

func _physics_process(delta):
	ttl -= delta
	match state:
		STATES.FIRED:
			var collision: KinematicCollision2D = move_and_collide(velocity * delta)
			if collision: _on_collision(collision.get_collider(), collision.get_position())
			
			var rq = PhysicsRayQueryParameters2D.create(_last_pos, position, collision_mask)
			rq.collide_with_areas = true
			var res: Dictionary = get_world_2d().direct_space_state.intersect_ray(rq)
			if res.has("collider"):
				_on_collision(res.collider, res.position)
				position = res.position
			elif ttl <= 0:
				state = STATES.EXPIRED
		# ...

It’s definitely a hack, though. The move_and_collide should be replaced by the ray query. Using both instructions together could result in an even weirder situation; move_and_collide could skip a collision object (the issue we’re trying to fix with the ray query), but then still collide with a different collision object. Then the ray query redoes the same movement and collides with the first object that was missed by move_and_collide . Depending on the game, that could mean something like randomly shooting through shields or walls under specific circumstances.

The current approach is essentially a two-pass solution, where the first pass is sloppy, and the second pass works as intended, but doesn’t move the projectile.

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