RichTextLabel clipping ignores rotation.

[Jubjub]

Godot version:
b77a411 (latest master)

Issue description:
When the text overflows in a rotated RichTextLabel, it gets clipped to an axis-aligned rect instead of a rotated rectangle.

Steps to reproduce:
Create RichTextLabel with enough text that it overflows, and rotate it, or its parent.

[toger5]

It si weired how the clipping works though... seems strange, that only the bottom left corner is clipped without rotation. Clipping box might be bigger...
I did changes to clipping, so i should look at it. Didn't think about rotation back than. The issue i fixed was about rendering viewports to textures.

[Jubjub]

Thanks for taking a look.
Actually if you rotate it around you'll see that the clipping box is something like this:

I tried to fix it myself but only got as far as seeing that the clipping rect is set in https://github.com/godotengine/godot/blob/master/scene/gui/control.cpp#L605 but I'm not familiar enough with the internals to know how to apply the control's rotation to that.

Maybe it's because it uses a glScissor in the driver, and that isnt affected by transforms? Not sure.

[toger5]

Yea i think the glScissors is the issue. As u said, somewhere in the drivers/visual server file (there are two one for gles2 and one for gles3)
Don't know if the clipping can be applied before the transform?

[Jubjub]

I was researching this last night, but as far as I can see the glScissor test is just a viewport thing that can't have transforms applied to it. One way to solve it would be to check for rotation, and then use a stencil test instead, which can be any arbitrary shape.

[KoBeWi]

Related: #20671

[KoBeWi]

Still valid in a6d4484

[Calinou]

Duplicate of #20671.