Texture component swizzle 🥤

[beaufortfrancois]

This issue tracks CTS tests for Texture component swizzle proposal:

• Works with all textures and is validated out.
• Swizzle for storage textures.
• Depth textures used as texture_depth
• Depth textures used as texture_2d
• Stencil textures used as texture_2d
• Multisampled color textures.
• Multisampled depth textures.
• Also the various ways to use the view: Load/Fetch, Sampling, Gather, maybe the compare versions etc.

[beaufortfrancois]

@greggman As I'm adding support in dawn.node, would you be willing to write some CTS tests for the proposed texture component swizzle feature?

[beaufortfrancois]

FYI https://beaufortfrancois.github.io/sandbox/webgpu/texture-component-swizzle.html works for me in Chrome Canary 🐤 on macOS with chrome://flags/#enable-unsafe-webgpu flag enabled. Vulkan and D3D12 support dawn CLs are in review.

[greggman]

Yes, I'm happy to write some tests

[beaufortfrancois]

Thank you very much!

[greggman]

Do we know that swizzle works with depth textures? In particular for textureGatherCompare

What I see on Mac M1 in Chrome Canary using texture-component-swizzle it doesn't seem to make any sense.

options:

1. GPU gathers four, 4 channel (vec4f) texels, swizzles each, takes the R value from each, compares

   this would make setting any swizzle to 'g', 'b', 'a' implementation defined
   since only r is defined. It would also mean setting a swizzle to zero or
   one happens before the compare.

2. GPU gathers four, 1 channel depth values, swizzles, compares

   this would also mean the comparison happens on the swizzled value so passing in
   one would fail ref(0.5) < value and pass ref(0.5) > value

3. GPU gathers four, 1 channel depth values, compares, swizzles

   this would mean a swizzle of one or zero overrides the comparison

So here's M1 via Chrome Canary

texels: 0.2, 0.4, 0.6, 0.8
gather: a    b    g    r     

compare: less , ref: 0.5
r g b a
1,1,0,0 swizzle: {}
1,1,1,1 swizzle: {r:'one',b:'one',g:'one',a:'one'}
0,0,0,0 swizzle: {r:'zero',b:'zero',g:'zero',a:'zero'}
1,1,1,1 swizzle: {r:'a',b:'g',g:'b',a:'r'}
1,1,0,0 swizzle: {r:'r',b:'r',g:'r',a:'r'}
1,1,0,0 swizzle: {r:'g',b:'g',g:'g',a:'g'}
1,1,0,0 swizzle: {r:'b',b:'b',g:'b',a:'b'}
1,1,1,1 swizzle: {r:'a',b:'a',g:'a',a:'a'}

compare: greater , ref: 0.5
r g b a
0,0,1,1 swizzle: {}
1,1,1,1 swizzle: {r:'one',b:'one',g:'one',a:'one'}
0,0,0,0 swizzle: {r:'zero',b:'zero',g:'zero',a:'zero'}
1,1,1,1 swizzle: {r:'a',b:'g',g:'b',a:'r'}
0,0,1,1 swizzle: {r:'r',b:'r',g:'r',a:'r'}
0,0,1,1 swizzle: {r:'g',b:'g',g:'g',a:'g'}
0,0,1,1 swizzle: {r:'b',b:'b',g:'b',a:'b'}
1,1,1,1 swizzle: {r:'a',b:'a',g:'a',a:'a'}

one and zero seem to be overwrite the comparison since one and zero always return 1 and 0 even when the comparison is swapped from less to greater which suggests (3). But, when setting them all to r, g, or b it still getting different values for each channel which suggests (1)

I tried it in OpenGL 4.1 on MacOS

https://github.com/greggman/macos-opengl-experiments/blob/main/macos-opengl-textureGatherCompare/examples/example_apple_opengl2/main.mm

There TEXTURE_SWIZZLE had no effect. I'm not sure if it's supposed to or not.

texels: 0.2, 0.4, 0.6, 0.8
gather: a    b    g    r     

compare: less
1 1 0 0 : swizzle: r g b a
1 1 0 0 : swizzle: 1 1 1 1
1 1 0 0 : swizzle: 0 0 0 0
1 1 0 0 : swizzle: r r r r
1 1 0 0 : swizzle: g g g g
1 1 0 0 : swizzle: b b b b
1 1 0 0 : swizzle: a a a a
1 1 0 0 : swizzle: a b g r

compare: greater
0 0 1 1 : swizzle: r g b a
0 0 1 1 : swizzle: 1 1 1 1
0 0 1 1 : swizzle: 0 0 0 0
0 0 1 1 : swizzle: r r r r
0 0 1 1 : swizzle: g g g g
0 0 1 1 : swizzle: b b b b
0 0 1 1 : swizzle: a a a a
0 0 1 1 : swizzle: a b g r

Do we know what other APIs do here? Is this even used or should we just disallow swizzle with depth textures period?

[greggman]

wrote a directx 12 test (well, Claude wrote it)

texels: 0.2, 0.4, 0.6, 0.8
gather: a    b    g    r     

Comparison mode: LESS
1.0 1.0 0.0 0.0 - default
1.0 1.0 1.0 1.0 - one one one one
0.0 0.0 0.0 0.0 - zero zero zero zero
1.0 1.0 0.0 0.0 - r r r r
0.0 0.0 0.0 0.0 - g g g g
0.0 0.0 0.0 0.0 - b b b b
1.0 1.0 1.0 1.0 - a a a a
1.0 1.0 1.0 1.0 - a b g r

Comparison mode: GREATER
1.0 1.0 0.0 0.0 - default
1.0 1.0 1.0 1.0 - one one one one
0.0 0.0 0.0 0.0 - zero zero zero zero
1.0 1.0 0.0 0.0 - r r r r
0.0 0.0 0.0 0.0 - g g g g
0.0 0.0 0.0 0.0 - b b b b
1.0 1.0 1.0 1.0 - a a a a
1.0 1.0 1.0 1.0 - a b g r

I think based on this it works where it reads 4 vec4s, does the comparison on each (16 compares), then swizzles, then gathers.