Incorrect bounce angle of RigidBody2D when using the Cast Ray Continuous Cd mode

[GaidamakUA]

Godot version:
v3.1.1.stable.official
OS/device including version:
Mac OS X and Linux Ubuntu
Issue description:
RigidBody2d collides with flat StaticBody2d and bounces with random angle. Often, with the same it came from. Happens on relatively high speed of RigidBody2d
Steps to reproduce:

1. Run the project
2. Bump the RigidBody2d with KinematicBody2d so it's speed increases
3. Observe the bug.

Here are the description with video and screenshots attached:
https://www.reddit.com/r/godot/comments/d4455z/bug_i_godot_physics_system/
Minimal reproduction project:
https://github.com/GaidamakUA/GodotExperiments/tree/master/arcanoid

[ghost]

Setting "Continuous Cd" on the Ball to "Cast Shape" seems to make it behave correctly (tested with 3.2-alpha 24e1039). I couldn't tell you why though.

[GaidamakUA]

Yes, I can confirm, it works with "Cast shape". Thanks. Just to give you a bit more context. I've tried to implement borders in previous version by collision shape in TileMap. And it behaved in a similar manner. And "Cast Shape" didn't work. You need me to make another sample project for that?

[ghost]

@GaidamakUA Yeah that would definitely help, if it isn't too much trouble.

[GaidamakUA]

It's pretty same but collision is implemented via tilest
https://github.com/GaidamakUA/GodotExperiments/tree/master/arcanoid_tileset_collision
For this version Cast Shape doesn't fix the issue.
@Homer666

[Feniks-Gaming]

https://www.reddit.com/r/godot/comments/eerh7a/why_is_my_bouncing_inconsistent/

I have the same issues in my project using 3.1

[maximinus]

I have exactly the same issue. I would guess the object is travelling inside the static body and this is causing it to lose accuracy somewhere. I have seen this on Windows 10 and Linux. The issue can be reduced somewhat with a slower moving object and "Cast shape" a little better but cannot remove it totally.

[Feniks-Gaming]

I can confirm what @maximinus is saying using a square rather than circle collision shape, using cast shape collision reduces this significantly but doesn't fix the issue fully. As result if one was to create a bouncing ball that goes down and bounces up on collision it would eventually start bounding other angle and at different speed despite no other forces being used.

What is worse documentation suggest that RidigBody2d should be exatly what we are supposed to use for simple games where we want ball to collide with some blocks.

[jtaart]

The contact seems to be flipped. Don't exactly know whats going on with the function, but it seems a little off.

godot/servers/physics_2d/body_pair_2d_sw.cpp

Lines 214 to 217 in 24e1039

	if (p_swap_result)
	_contact_added_callback(contact_B, contact_A);
	else
	_contact_added_callback(contact_A, contact_B);

flipped gif
unflipped gif
temp fix gif

[madmiraal]

This may be related to #28438. It appears to occur when colliding with the point between two CollisionShapes. Since it calculates the collisions separately, there is a collision with the corner of one shape i.e. a little bit of the edge between the shapes.

[Yolwoocle]

This still seems to happen in 4.2.1. Is there any plan for a fix? It's been 4 years.