The description in "Lights and Shadows" of the 'Reverse Cull Faces' option lacks important information

[Two-Tone]

It's the last bullet point in this section.

The info it lacks is that it doesn't mentioned that when enabled you'll need to set the bias to a negative number because if you don't you'll end up with a huge gap between the shadow and the object casting it, one that you can't fix by just adjusting the contact option as you'll end up with very broken looking shadows.

However, a negative bias will result in the shadows "bleeding" weirdly, even with a bias that is barely into the negative. This can be worked around by having the bias at or barely below 0 and then barely upping the Contact value, but that results in a weird graphical glitch on any faces that are at a shallow angle to the light source, that might be a bug with Contact though?

I'd also like for it to mention where enabling Reverse Cull Faces is useful as the current description doesn't tell you anything.

[Calinou]

that might be a bug with Contact though?

Contact shadows are known to be broken and may be hidden from the editor in the future. See godotengine/godot#35316.

[Two-Tone]

Instead of hiding it, wouldn't it be better to fix it?

[Calinou]

@Two-Tone I have no idea how to fix it, and reduz is busy working on the Vulkan renderer 🙁

There are performance issues with contact shadows when you get up close anyway. I haven't seen any AAA game use this kind of shadows, so it's probably not the way forward. Tweaking shadow rendering to make acne less visible is likely a better solution, see godotengine/godot#17260.

[Two-Tone]

CptPotato's work in there looked great, I wonder why he thought it wasn't ready. I wonder what it looks like with the camera moving.

[Skaruts]

I seem to get good results with 0.001 bias and reverse cull face.

Without reverse cull face, if I lower the bias enough to leave no gaps (below 0.01), I always get self-shadowing artifacts. But then with 0.001 bias, if I turn reverse cull face on, then everything seems to look just right. No gaps, no artifacts.

Is this the intended behavior/usage of that setting?

[Calinou]

Without reverse cull face, if I lower the bias enough to leave no gaps (below 0.01), I always get self-shadowing artifacts. But then with 0.001 bias, if I turn reverse cull face on, then everything seems to look just right. No gaps, no artifacts.

Is this the intended behavior/usage of that setting?

Reverse cull face is best used with a slight negative bias (between -0.01 and -0.01), but don't enable contact shadows at the same time.

Either way, the documentation on the subject was recently improved, so I'll close this.