Fix the WebGL 2 backend by giving the visibility_ranges array a fixed length.

[pcwalton]

WebGL 2 doesn't support variable-length uniform buffer arrays. So we arbitrarily set the length of the visibility ranges field to 64 on that platform.

[IceSentry]

Added a suggestion with a comment to explain what you said in the description

[IceSentry]

Suggested change

	@group(0) @binding(12) var<uniform> visibility_ranges: array<vec4<f32>, 1024u>;
	// In WebGL2 we never loop over this array so the size number is not important. We only set it to something so it compiles correctly
	@group(0) @binding(12) var<uniform> visibility_ranges: array<vec4<f32>, 1024u>;

[IceSentry]

I just tested it and it gives me a new error. The error seems to be that arrayLength doesn't work with fixed size uniform buffer array. That's really annoying but a way to avoid this error seems to be to use this ugly hack inside get_visibility_range_dither_level():

    #if AVAILABLE_STORAGE_BUFFER_BINDINGS >= 6
    if (visibility_buffer_index > arrayLength(&visibility_ranges)) {
        return -16;
    }
    #else
    // In WebGL2 we use a uniform buffer array with a fixed size and this doesn't work with arrayLength()
    if (visibility_buffer_index > 1024u) {
        return -16;
    }
    #endif

It gets rid of the error but no meshes are visible. I'm not sure if that's expected.

[kristoff3r]

I just tested it and it gives me a new error. The error seems to be that arrayLength doesn't work with fixed size uniforme buffer array. That's really annoying but a way to avoid this error seems to be to use this ugly hack inside get_visibility_range_dither_level():

    #if AVAILABLE_STORAGE_BUFFER_BINDINGS >= 6
    if (visibility_buffer_index > arrayLength(&visibility_ranges)) {
        return -16;
    }
    #else
    // In WebGL2 we use a uniform buffer array with a fixed size and this doesn't work with arrayLength()
    if (visibility_buffer_index > 1024u) {
        return -16;
    }
    #endif

It gets rid of the error but no meshes are visible. I'm not sure if that's expected.

Weird, on this PR I don't get this error on the 3d_scene example where I encountered the original error, it just seems to work. Which example are you running?

[IceSentry]

Ah, yeah, that's when running the visibility_range example. I should have clarified. It still shows the shadows but not the mesh.

[IceSentry]

I don't get any error in 3d_scene in webgl2 on main personally. So I didn't realize the error was in another example.

[kristoff3r]

I don't see the errors that IceSentry is seeing, which is weird, but this definitely fixes it for me.

[pcwalton]

OK, I was wrong here: WebGL 2 actually does require the size to be exact if you end up using the UBO. So I set the size arbitrarily to 64. This fixes all the issues for me.

[IceSentry]

This resolved all the issues for me too.

I'll make a PR to your branch with this suggestion. It's possible to use a const instead of the hard coded value so we don't have to change it in 2 places. It's not a blocker though. I'd rather get this merged quickly to fix the error. We could even use shader_defs for that I think, but this would require a few more changes because that would be the first case of shader_defs that only exist for the mesh_view_bindings. So definitely out of scope here.

[pcwalton]

Sure, that sounds good. I merged your PR.