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floooh / sokol

minimal cross-platform standalone C headers
https://floooh.github.io/sokol-html5
zlib License
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Mipmaps on GL/GLES require GL_TEXTURE_MAX_LEVEL set explicitly. #911

Closed ambrusc closed 9 months ago

ambrusc commented 9 months ago

Problem: Any texture with a mipmap sampler was black on GL/GLES but working on e.g. Metal (ARM). Cause: GL texture was incomplete: (See: mipmap completeness, mipmap range) Fix: set GL_TEXTURE_MAX_LEVEL based on num_mipmaps when creating the texture. Verified: textures load with mipamp samplers on desktop GL 3.3 (Manjaro) and WASM (Emscripten, GLES3, Firefox).

Hopefully this fix is conceptually in the right place in the code. Let me know if not, and I can update.

As an aside, this approach doesn't support loading smaller LODs progressively into mip levels over several frames like many engines do. Not sure if any of the other backends support such usage, so the point may be moot.

floooh commented 9 months ago

Hmm, this is a bit strange because mipmapping is working here in dedicated testing sample.

https://floooh.github.io/sokol-html5/mipmap-sapp.html

Can you post your texture creation code here? Because with the sokol-gfx validation layer active it should actually be impossible to create a texture with an incomplete mipmap chain. I guess there must be a bug in the validation layer, or an edge case which I didn't think of.

Thanks!

ambrusc commented 9 months ago

Do I need to add an include or something on Windows?

ambrusc commented 9 months ago

Hmm, this is a bit strange because mipmapping is working here in dedicated testing sample.

https://floooh.github.io/sokol-html5/mipmap-sapp.html

Can you post your texture creation code here? Because with the sokol-gfx validation layer active it should actually be impossible to create a texture with an incomplete mipmap chain. I guess there must be a bug in the validation layer, or an edge case which I didn't think of.

Thanks!

Oh nice, hopefully it's user error on my part. Let me take a look at the sample.

floooh commented 9 months ago

Do I need to add an include or something on Windows?

On Windows sokol_gfx.h uses its own GL loader, you'd need to add a line here:

https://github.com/floooh/sokol/blob/master/sokol_gfx.h#L3910

The value for GL_TEXTURE_MAX_LEVEL is:

#define GL_TEXTURE_MAX_LEVEL 0x813D
floooh commented 9 months ago

Oh nice, hopefully it's user error on my part. Let me take a look at the sample.

In any case let me know what you find out, because as I wrote above, it should actually be impossible to create an incomplete mipmap chain due to the validation layer.

ambrusc commented 9 months ago

Ahh! Okay I have a repro. It has to do with non-square images. My reading of the GL spec suggests they support non-power-of-two (NPOT) mipmaps (rounding sizes down) as well, but I haven't tried yet.

Here's the quick and dirty code: https://github.com/floooh/sokol-samples/compare/master...ambrusc:sokol-samples:master?diff=split

Is this user error, or a bug in the library, or a bug in the validation layer?

Happy to help in any way I can :-)

floooh commented 9 months ago

...non-power-of-two (NPOT)...

Ok interesting! It's my impression as well that NPOT images with mipmaps were only restricted in GLES2/WebGL1, but those restrictions don't apply in desktop GL, GLES3 and WebGL2. I'll definitely need to investigate this (and I don't understand yet why setting GL_MAX_TEXTURE_LEVEL would help).

The restrictions in GLES2/WebGL were that non-power-of-two textures must have no mipmaps, and must be filtered with CLAMP_TO_EDGE. But since GLES2 support has been removed I didn't think it important to have validation layer checks for this.

Rectangular textures with power-of-2 dimensions shouldn't have any restrictions though.

I'll log off for today, but will investigate the issue over the next few days (looking at your sokol-samples changes I have a hunch that it's about the number of mipmaps, e.g. that a 256x128 texture needs 8 mipmaps, in any case - this should trigger a validation layer error).

ambrusc commented 9 months ago

Okay, by playing with the mipmap-sapp sample with various combination of NPOT and non-square textures, I think I have a reasonable handle what's going on.

  1. GL defines rules for mipmap completeness, which I was inadvertently breaking by not generating the smallest N mipmaps.
  2. This is okay, as long as you set GL_TEXTURE_MAX_LEVEL correctly for the number of mipmaps actually generated, which is why this fix works and is probably worth making.
  3. If you don't set GL_TEXTURE_MAX_LEVEL explicitly but generate mipmaps down to the smallest 1x1 image, GL considers the texture to be complete (I have not found the docs as to why is the case, but it appears to work empirically as the samples were depending upon it until now).
floooh commented 9 months ago

Makes sense yeah, I'll need to add an incomplete mip chain to the mipmap sample and see what happens on the other backends, and also maybe tighten up the validation layer. I think the whole topic of complete versus incomplete mip chains was too murky so far...

floooh commented 9 months ago

Apologies, I'll close this PR in favour of https://github.com/floooh/sokol/pull/924

(I also added more detailed error logging for the GL framebuffer completeness check there)

The PR will be merged together with new sokol-samples which cover rendering to mipmaps (and maybe texture-array-layers and 3D-texture-slices).

ambrusc commented 9 months ago

Awesome, thank you so much! 🎉