op: rendering,blending

[kainino0x]

No description provided.

[kainino0x]

This item refers to api/operation/rendering/blending.ts.
That file is partly implemented, but has a number of "unimplemented" tests at the bottom. These need to be fleshed out and implemented:
https://github.com/gpuweb/cts/blob/main/src/webgpu/api/operation/rendering/blending.spec.ts#L277

Example: formats : "Test blending results works for all formats that support it, and that blending is not applied for formats that do not. Blending should be done in linear space for srgb formats."

This description needs to be updated - it's a validation error to attempt to use blending with a format that doesn't support it. (We should check we have a validation test for that before deleting it from this test description.)

This test would:

• Set up a basic render pipeline like this one, with some basic blend states, for example { operation: "add", srcFactor: "one", dstFactor: "one" } which should simply add the output of the fragment shader to the value currently in the buffer. From the fragment shader, output some value, like (0.4, 0.4, 0.4, 0.4).
• Set up a simple render pass with loadOp: "clear" and clearValue set to some value, like (0.2, 0.2, 0.2, 0.2).
• Ensure that the buffer contains the expected value, in this case would be (0.6, 0.6, 0.6, 0.6). Use a helper like textureContentIsOKByT2B to test the result with some error tolerance, because different formats will have different precisions. To start, try something like { maxDiffULPsForNormFormat: 1, maxDiffULPsForFloatFormat: 1 } but you will likely need to increase the tolerance, at least for maxDiffULPsForFloatFormat.

You can ignore the srgb formats thing for the moment, it should hopefully "just work" when you use textureContentIsOKByT2B.

Some documentation here https://gpuweb.github.io/cts/docs/tsdoc/functions/webgpu_util_texture_texture_ok.textureContentIsOKByT2B.html

[Gyuyoung]

@kainino0x Regarding clamp,blend_foo tests, I'm not clear what the fixed-point formats are, and how to list them up like kBlendableFormats[1]. In other words, I couldn't find what formats are the 'fixed-point' formats because it looks like there are no hints about fixed-point format in the tests.

[1] https://github.com/gpuweb/cts/blob/main/src/webgpu/api/operation/rendering/blending.spec.ts#L284

[kainino0x]

"fixed-point" refers to the unorm and snorm formats. We don't usually use that terminology so let's remove it and refer to unorm/snorm instead.

[Gyuyoung]

"fixed-point" refers to the unorm and snorm formats. We don't usually use that terminology so let's remove it and refer to unorm/snorm instead.

ok, then let me update the terminology with unorm/snorm in the PR.

[Gyuyoung]

I think we need to do minor things for this issue further. But, It's likely we've done major ones for this issue. So I'm not sure if we can mark this issue as 'complete'.

[kainino0x]

Let's file a new issue with a more specific title, so we can see exactly what it's about, with a pointer to what needs to be done (hopefully there's a code comment for it). Then we can mark this complete.

[Gyuyoung]

It looks like we can add more tests referring to the ColorStateTest in Dawn end2end test [1]. If I find available tests there, let me file a new issue for them.

[1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/dawn/src/dawn/tests/end2end/ColorStateTests.cpp;l=29?q=ColorStateTests&ss=chromium