Tilemap collision is not updated right away when changing tile (update done in the next collision resolution step)

[jusw85]

Godot version:
3.3

OS/device including version:
Arch Linux

Issue description:

I need to change a tile then query it's collision status immediately.

This works:

func _physics_process(delta):
	print($RayCast2D.is_colliding())

	if Input.is_action_just_pressed("ui_left"):
		print("Removing tile")
		$TileMap.set_cell(1, 0, -1)
		$TileMap.update_dirty_quadrants()
		$RayCast2D.force_raycast_update()
		print($RayCast2D.is_colliding())

True
True
Removing tile
False
False
False
False

This doesnt:

func _physics_process(delta):
	print($RayCast2D.is_colliding())

	if Input.is_action_just_pressed("ui_right"):
		print("Changing to different tile")
		$TileMap.set_cell(1, 0, 1)
		$TileMap.update_dirty_quadrants()
		$RayCast2D.force_raycast_update()
		print($RayCast2D.is_colliding())

True
True
Changing to different tile
False
True
True
True

Minimal reproduction project:

test2.zip

[akien-mga]

I think that's an expected limitation from the way collision checks are done. Recalculating collisions right away after each tilemap change could be very costly when doing bulk changes.

There could maybe be a method to force the PhysicsServer to reprocess shapes and collision for situations where it's wanted though.

[jusw85]

Sorry for bumping an old issue, but since I'm moving on past this project and closing the issue for myself, I present my use case and thoughts for future reference for others (why I need to query collision status of tilemap in the same frame it was changed).

Simplified use case

• Player states are {Idle, Falling}
• Tiles are {Ground, CrackedGround}, both have collision
• Tiles can change from Ground => CrackedGround => destroyed
• Player is standing on Ground / CrackedGround
• Events can change tiles, which signals player to check for possible transition from Idle to Falling
• Changing tile from Ground to CrackedGround causes Raycast to report no collision on that frame, causing Player to incorrectly transition to Falling

Workarounds

• I can directly check against tile id instead of it's collision. But in a more complex example where only some tiles have collision and others don't, Player would be polluted with needing to know the collision state of all tiles
• I can delay the transition by one frame, after the collision resolution has been updated, but this has noticeable effect on responsiveness. If Ground is destroyed at Frame 10, Player should transition from Idle to Falling at end of Frame 10, and be Falling at start of Frame 11
• I could re-engineer my state machine transitions to the beginning of frame i.e. check for Idle => Falling transition at start of Frame 11. But... I don't think it really makes sense to perform FSM transitions at start of frame, I'd have to carry over too much state information from previous frame to the next frame