Unexpected behavior when setting negative scale in KinematicBody2D

[DragonFrai]

Godot version:
3.1-4a mono

OS/device including version:
Linux Mint 19.1

Issue description:
You try to set the scale.x < 0 for KinematicBody2D, RigidBody2D, and (possibly) StaticBody2D from code, scale changes sign to opposite (-1, 1) -> (1, -1); (-1, -1) -> (1, 1). In this case, the scale actually changes, but the resulting scale is not correct.

In the attached project in _Ready, we change the original scale (1, 1) to (-1, -1). The body changes its scale, but the scale in _physics_process is now (1, 1).

Minimal reproduction project:
KinematicScale.zip

[timoschwarzer]

Please describe "strange behavior" more in detail. (Maybe with a video/GIF, https://github.com/phw/peek)

[DragonFrai]

    if (Input.IsActionPressed("ui_left"))
    {
        Velocity.x = -WalkSpeed;
        
        if (_animPlayer.GetCurrentAnimation() != "move")
            _animPlayer.Play("move");
        
        var scale = Scale;
        if (scale.x > 0)
        {
            scale.x = -1f;
            Scale = scale;
        }
    }
    else if (Input.IsActionPressed("ui_right"))
    {
        Velocity.x = WalkSpeed;
        
        if (_animPlayer.GetCurrentAnimation() != "move")
            _animPlayer.Play("move");
        
        var scale = Scale;
        if (scale.x < 0)
        {
            scale.x = 1f;
            Scale = scale;
        }
    }

2018-12-30 21-37-18.flv.zip

[timoschwarzer]

I think this code sample is not the problem's source. (At least didn't find anything yet)
But I wonder why you get and set the Scale property instead of just setting Scale.x...

[DragonFrai]

About Scale.x

Here's a simpler example. Perhaps this is documented behavior KinematicBody2D (I have not tested other objects).

The screenshots show that once the Scale.x < 0, then x and y change their sign.
This project contains only 1 script and only nodes in the main scene.
The first call to _Physics Process Scale remains true, but the first call to _Process Scale has already changed.

Godot version:
3.1-4a mono

OS including version:
Linux Mint 19.1

Mono version:
5.12.0.301

msbuilde version:
Microsoft (R) Build Engine version 15.6.0.0 ( Thu May 10 14:00:26 UTC 2018) for Mono

[Zireael07]

I don't think we're supposed to set negative scale, ever.

[DragonFrai]

I still think it's weird that the Sprite for negative scale is supported, and for KinematicBody2D no. And when you set the scale in the editor, the body flips, but the scale remains positive in the code. But why scale negative only if scale.x < 0, by y the scale changes and remains the same?

The examples actually change the scale of the sprites. My mistake. I apologize if this is really the correct KinematicBody2D behavior

[timoschwarzer]

@Zireael07: partially true.
Setting negative scales is just fine in most cases. But: Scaling bodies, areas and collision shapes in general is bad and not intended. You should only scale the Sprite and not the whole body.

[DragonFrai]

Godot version:
3.1-4a mono

OS/device including version:
Linux Mint 19.1

Issue description:
You try to set the scale.x < 0 for KinematicBody2D, RigidBody2D, and (possibly) StaticBody2D from code, scale changes sign to opposite (-1, 1) -> (1, -1); (-1, -1) -> (1, 1). In this case, the scale actually changes, but the resulting scale is not correct.

In the attached project in _Ready, we change the original scale (1, 1) to (-1, -1). The body changes its scale, but the scale in _physics_process is now (1, 1).

Minimal reproduction project:
KinematicScale.zip

[timoschwarzer]

Related: #5734

[DragonFrai]

move_and_slide does inverts the KinematicBody scale. But does it only at scale.x < 0. If scale.y < 0 then nothing changes.

Initially, the body has a scale of 1, 1

In _ready, the body is reflected horizontally and stretched 2 times. The scale is changed to -2, 1

move_and_slide changes the scale of the body to 2, -1. But: visually and physically the body has a scale of -2, 1

[timoschwarzer]

@VAVUS7 yes, that's intended.
Quoting @reduz:

This is intended, because physics bodies manage their own transform which overwrites the ones you set.

That's probably not going to change soon.

So: Don't scale physics bodies.

[DragonFrai]

But the effect of manual scaling remains. And it is confusing. And again, why only with scale. x <0? Physical synchronization in KinematicBody simply sets the scale to 1, 1.