is_on_floor() detection is buggy

[vickylance]

Godot version:
v3.2.1

OS/device including version:
MacBook Pro - Catalina

Issue description:
is_on_floor() is returning true one frame and false another frame

Steps to reproduce:

1. Add a simple kinematic body and apply gravity only when not on floor this bug happens.

I have attached a below project with minimal reproduction

Minimal reproduction project:
MinimalProject

[Calinou]

Duplicate of #35780 (and possibly others).

[vickylance]

@Calinou But the KinematicBody is not in a GridMap or any edge. Its on a plain flat solid ground.
Also the capsule is not visibly jittering. Only the collision value returned is switching each frame. Also if I apply gravity on every frame instead, then its not happening.

[Calinou]

@vickylance I think it's still the same underlying issue 🙂

We have lots of issues reporting this exact problem. There are probably many duplicates lying around already.

[madmiraal]

@vickylance For is_on_floor() to return true, the previous call to move_and_slide() must result in a collision with the floor. If you update the velocity with the post collision velocity, after colliding with the floor the velocity in the y direction will be 0. However, if you also then choose not to apply gravity, the velocity passed to the next call to move and slide() in the y direction will be 0. Therefore, the next call to move_and_slide() won't result in a collision with the floor, and is_on_floor() correctly returns false.

[jcarlosrc]

This is not "correct". If the body is already colliding with the floor the physics engine should return true. This is, is_on_floor should return true if the body is already touching the floor even if vel.y is 0.