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:

godot/scene/2d/collision_polygon_2d.cpp

Lines 49 to 59 in 24e1039

	if (solids) {
	//here comes the sun, lalalala
	//decompose concave into multiple convex polygons and add them
	Vector<Vector<Vector2> > decomp = _decompose_in_convex();
	for (int i = 0; i < decomp.size(); i++) {
	Ref<ConvexPolygonShape2D> convex = memnew(ConvexPolygonShape2D);
	convex->set_points(decomp[i]);
	parent->shape_owner_add_shape(owner_id, convex);
	}

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 cb09abd.

The project in #25732 (comment) still reproduces the issue in the current master branch.

[capnm]

I can confirm #42574 fixes the issue (broken in 3.2.3.stable)
#25732 (comment)
in the 3.2 branch.