Add a debug draw mode for displaying UV2 (lightmap) texel density

[clayjohn]

Salvages and supersedes: #62987

This PR also implements instance uniforms for the Compatibility renderer as it was needed for the debug draw mode

Before merging:

• Rebase and squash all commits (maybe extract the change to add instance uniforms to a different PR Done Implement instance uniforms in Compatibility renderer #96819)
• Update so the texel scale updates without re-baking (right now baking isn't technically required by this technique, its just that the uv_scale is tied to the existing lightmap because of Add texel_scale property to LightmapGI #64908)
• Update documentation

Up close with bicubic filtering disabled so you can see individual texels. Note texels are aligned with the center of the square

Same as above but with bicubic on

Faint large scale checkerboard to easily tell scale

Looks fine from a distance

[passivestar]

Will this work with #75164?

[jcostello]

Will this work with #75164?

Good question. Ideally it should take any lightmap or mesh texel scale into account

[clayjohn]

Will this work with #75164?

Good question. Ideally it should take any lightmap or mesh texel scale into account

Right now it will automatically take #75164 into account since it uses the scale that was calculated during lightmap baking.

However, I need to refactor things so you can preview a new scale without re-baking.

[Calinou]

The checkerboard pattern in the screenshots looks a bit curious to me. Every 10 steps (when the large checkerboard changes color), it mirrors the pattern, which looks odd.

The number of steps between each large checkerboard step is also not a power of 2, so I think 8 steps would make more sense than 10 (since a lot of things in level design work with powers of 2). Contrast may need to be lowered slightly as well so it doesn't look overbearing in the process.

I'd expect it to look more like this instead (ignore the fact this is a 3-level checkerboard pattern, but look at the general contrast and the pattern not mirroring within each large checkerboard):

Note texels are aligned with the center of the square

This is also interesting to see; do any other programs do something similar? This may be confusing if the pattern drawn by Godot works differently to the one drawn by other 3D applications. I believe most of the time, the checkerboard pattern is exactly aligned with the texel grid as opposed to being offset by half a texel.

[clayjohn]

The checkerboard pattern in the screenshots looks a bit curious to me. Every 8 steps (when the large checkerboard changes color), it mirrors the pattern, which looks odd.

I'd expect it to look more like this instead (ignore the fact this is a 3-level checkerboard pattern):

I originally had it like this, but it looks horrible with the 2-level checkerboard. the dark tiles of the light squares end up being close to the light tiles of the dark squares, so you see this weird pattern over everything. In your screenshot, the 3rd level really helps break it up

This is also interesting to see; do any other programs do something similar? This may be confusing if the pattern drawn by Godot works differently to the one drawn by other 3D applications. I believe most of the time, the checkerboard pattern is exactly aligned with the texel grid as opposed to being offset by half a texel.

I think you misunderstand. This is exactly aligned with the texel grid. I don't know what other programs do, but I think the most intuitive thing is for the squares to a visual representation of the pixel (if you consider the pixel as a little square). So the center of the pixel should sit in the center of the square.

[Calinou]

In your screenshot, the 3rd level really helps break it up

That's interesting, I didn't think about it before. Here's the texture if you need it (CC0):

[jcostello]

@clayjohn after this is merge #75164 can you take it in count for the texel density?

[clayjohn]

@clayjohn after this is merge #75164 can you take it in count for the texel density?

I think so!