On tiled physics ground or walls, prevent collision with wrong edge?

Davbo · February 17, 2020, 10:34pm

Hi all,

I’m beginning development of a platformer. I’m loading a tilemap and using it for collision. I have an issue where as my character walks along the ground they will sometimes collide with the left or right edges of each ground tile, causing them to lose their velocity. The same problem occurs when falling against a wall - the player can collide with the bottom and top of individual wall tiles making them bump their head or be able to land on sections of the wall.

To demonstrate the issue I branched a simple platformer test and added in some acceleration and found the same issues. If you run this project and walk along the ground you’ll find sometimes your velocity will be cancelled even though it doesn’t look like you’ve hit anything and if you jump while pressing into a wall you’ll bump your head then land in the wall.

The player script is here:

github.com

davidjtferguson/publicexamples/blob/master/examples/one_way_platforms/one_way_platforms/one_way_platforms_player.script

-- gravity pulling the player down in pixel units/sˆ2
local gravity = -20

-- take-off speed when jumping in pixel units/s
local jump_takeoff_speed = 900

function init(self)
	-- this tells the engine to send input to on_input() in this script
	msg.post(".", "acquire_input_focus")
	msg.post("camera", "acquire_camera_focus")
	--msg.post("@system:", "toggle_physics_debug")

	-- save the starting position
	self.position = go.get_position()

	-- keep track of movement vector and if there is ground contact
	self.velocity = vmath.vector3(0, 0, 0)
	self.max_velocity_x = 250
	self.acceleration_x = 15
	self.ground_contact = false

This file has been truncated. show original

Any suggestions on how to tackle this? I was trying to filter out collisions or velocity resets based on the collision info but couldn’t think of logic that would do that without breaking the collision in other ways. If there was a way to combine adjacent tiles’ physics colliders if they’re the same so each ground or wall was one physics object that would be best, is there a way to do that?

Anthroyd · February 17, 2020, 11:45pm

This was discussed recently:
https://forum.defold.com/t/merge-tile-colliders

Also analyzed a while back:
https://forum.defold.com/t/directional-platforms-help

It’s difficult to get this working. You can switch to using ray casts instead of collision shapes between your tile map and characters. A helpful library in remedying this problem can be found here:

sergey.lerg · February 18, 2020, 12:38pm

Defold can’t merge those tiles together to remove unwanted edges.
I am working on an alternative extension for box2d, where you can programmatically set width/height of each physics body. It’s more work, but should help with the issue. If you are interested you can try it via my Patreon.

Davbo · February 18, 2020, 5:47pm

Huh, I thought it would be a pretty standard problem so expected a standard solution. Oh well. Thanks for the leads, I’ll give Platypus a try!

Anthroyd · February 27, 2020, 7:47pm

Is Platypus working out for you? I’m having problems with the raycasts allowing me to clip into tiles.

britzl · February 27, 2020, 9:23pm

Did you configure it properly and specify raycast distance?

Davbo · February 28, 2020, 11:06am

Yeah, I got it working. Had to muck around with the left, right, up, down and offset in the config for a bit to get collision to work properly. I figured it out from the example project in the platypus repo. Also if your character can move fast enough that they can get most the way through a tile in one frame they’ll get pushed out the other end so that might also be your problem?