Possible incorrect handling of texture arrays in GLSL

[spencerkohan]

I'm using naga to create a module out of the following frgment shader:

            #version 450

            layout(location=2) in  vec2 uv;

            layout(set = 0, binding = 0) uniform texture2D glyphTextures[256];
            layout(set = 0, binding = 1) uniform sampler glyphSampler;

            void main() {
                vec4 tex = texture(
                    sampler2D(glyphTextures[0], glyphSampler),
                    uv
                );

                f_color = tex;
            }

If I inspect the resulting module, the type of the global variable named "glyphTexutures" is:

Type {
    name: None,
    inner: Array {
        base: [4],
        size: Constant(
            [5],
        ),
        stride: 0,
    },
}

According to the documentation, it looks like my type inner should be TypeInner::BindingArray rather than Array, right?

[teoxoy]

The initial implementation didn't cover all frontends (only the wgsl one). See gfx-rs/naga#1845 (comment) and #4313.

[djeedai]

Just to confirm that I hit this in real-world code, which manifests as a panic on some unreachable!() (which is kind of scary, and not very explanatory).

• naga::back::glsl::Writer::write_global() will get a global.space == AddressSpace::Handle which has an unreachable!() in the match case.
• The caller only handles TypeInner::Image and TypeInner::Sampler, assuming that this is enough to handle all Handles, which is not the case for a binding array.

Original WGSL code which got translated had:

@group(0) @binding(13) var diffuse_environment_maps: binding_array<texture_cube<f32>, 8u>;

[cwfitzgerald]

The problem you're hitting is a different one than the original issue. OpenGL doesn't support binding arrays, so we can't actually emit glsl for that binding.

[djeedai]

Oh sorry, I mixed texture arrays and binding arrays, wrong issue my bad.

[cwfitzgerald]

I want to note the original issue is using binding arrays - this is just a GLSL frontend issue (we accept vulkan flavored glsl) whereas you're having a backend issue (we output OpenGL flavored glsl). OpenGL flavor glsl doesn't support binding arrays.

[djeedai]

Should I open a separate one for the fact the code reaches an unreachable!(), which even if GLSL doesn't support array bindings feels like a lack of error handling which at best shouldn't panic, or at least should assert with a dedicated condition and error message?