Godot: CollisionPolygon2D fall through with One Way Collision enabled

[DleanJeans]

Godot version: Godot 3.1 Beta 3

OS/device including version: Windows 10

Issue description:

Steps to reproduce:
Seems to happen only when the body with polygon is moving upwards

Minimal reproduction project:

OneWayPolygonCollision.zip

[DleanJeans]

OneWayPolygonCollisionWater.zip

[reduz]

Sorry, I quit programming, I'll go open a farm.

[DleanJeans]

This doesn't seem like CollisionPolygon2D exclusive. A RigidBody2D character can go through a rectangle StaticBody2D wall at times. This is more like a universal bug with One Way Collision.

[andrejp88]

I just ran into this same issue. In my case I have a capsule-shaped KinematicBody2D (player) falling through a segment-shaped StaticBody2D. Out of the following 5 segments, it only occurs with the one marked X:

That one is at y=130, and if I remove it and place another identical platform at that coordinate, the player falls through again. So it seems to be tied to the position. If I set its "One Way Collision Margin" to 1.4 or higher, then the player won't fall through but will instead rapidly vibrate up and down by 1 pixel while standing on it, so unfortunately that's not a solution.

(Using 3.1.1 stable)

[njt1982]

I've had some luck by manually replicating this:
https://github.com/godotengine/godot/blob/24e1039eb6fe32115e8d1a62a84965e9be19a2ed/scene/2d/collision_polygon_2d.cpp#L49-L59

So.. in my case I have a "terrain" which I was trying to apply ConcavePolygonShape2D and ConvexPolygonShape2D to without success. This terrain is an array of points (defining the heightmap) rendered using draw_polyline.
What I am doing now is looping over all the points from zero to length-1 and creating individual convex triangles for each i, i+1 and a "bottom" vector2.

This seems to have fixed it for mel it's made all my terrain edges "solid".

[akien-mga]

For the reference, the project in OP no longer reproduces the issue, as it was fixed by cb09abdbbdb.

The project in https://github.com/godotengine/godot/issues/25732#issuecomment-466669002 still reproduces the issue in the current master branch.

[capnm]

I can confirm #42574 fixes the issue (broken in 3.2.3.stable)
https://github.com/godotengine/godot/issues/25732#issuecomment-466669002
in the 3.2 branch.