Conversion from rgba to rg8unorm should copy correct pixel values

https://bugs.webkit.org/show_bug.cgi?id=270558
rdar://123810638

Reviewed by Mike Wyrzykowski.

* LayoutTests/fast/webgpu/conversion-to-rg8unorm-expected.txt: Added.
* LayoutTests/fast/webgpu/conversion-to-rg8unorm.html: Added.
* Source/WebCore/Modules/WebGPU/GPUQueue.cpp:
(WebCore::copyToDestinationFormat):

Canonical link: https://commits.webkit.org/275738@main

LayoutTests/fast/webgpu/conversion-to-rg8unorm-expected.txt

@@ -0,0 +1 @@
+This test passes if it does not crash.

LayoutTests/fast/webgpu/conversion-to-rg8unorm.html

@@ -0,0 +1,80 @@
+<script>
+if (window.testRunner) { testRunner.dumpAsText(); testRunner.waitUntilDone() }
+onload = async () => {
+  try {
+    let adapter0 = await navigator.gpu.requestAdapter(
+    {
+    }
+    );
+
+    let device0 = await adapter0.requestDevice(
+    {
+    label: 'a',
+    requiredFeatures: [
+    'depth-clip-control',
+    'texture-compression-etc2',
+    'texture-compression-astc',
+    'indirect-first-instance',
+    'shader-f16',
+    'rg11b10ufloat-renderable',
+    'bgra8unorm-storage'
+    ],
+    requiredLimits: {
+    maxVertexAttributes: 23,
+    maxVertexBufferArrayStride: 46861,
+    maxStorageTexturesPerShaderStage: 33,
+    maxBindingsPerBindGroup: 1499,
+    },
+    }
+    );
+
+    let canvas0 = document.createElement('canvas');
+    let imageBitMap0 = await createImageBitmap(canvas0);
+
+    let videoFrame1 = new VideoFrame(imageBitMap0, {timestamp: 0});
+
+    let texture0 = device0.createTexture(
+    {
+    label: 'a',
+    size: {
+    width: 373,
+    depthOrArrayLayers: 1,
+    },
+    mipLevelCount: 6,
+    sampleCount: 1,
+    format: 'rg8unorm',
+    usage: GPUTextureUsage.STORAGE_BINDING | GPUTextureUsage.RENDER_ATTACHMENT,
+    }
+    );
+
+    device0.queue.copyExternalImageToTexture(
+    {
+    source: videoFrame1,
+    origin: {
+    x: 2707,
+    y: 4310,
+    },
+    },
+    {
+    texture: texture0,
+    mipLevel: 2591,
+    origin: [
+    5319,
+    466,
+    9625,
+    6005,
+    622
+    ],
+    aspect: 'stencil-only',
+    colorSpace: 'srgb',
+    premultipliedAlpha: true,
+    },
+    [
+    4191
+    ]
+    );
+  } catch { }
+  if (window.testRunner) { testRunner.notifyDone() }
+};
+</script>
+This test passes if it does not crash.

Source/WebCore/Modules/WebGPU/GPUQueue.cpp

@@ -541,7 +541,7 @@ static void* copyToDestinationFormat(const uint8_t* rgbaBytes, GPUTextureFormat
 
     case GPUTextureFormat::Rg8unorm: {
         uint8_t* data = (uint8_t*)malloc(sizeInBytes / 2);
-        for (size_t i = 0, i0 = 0; i < sizeInBytes; i += 2, ++i0) {
+        for (size_t i = 0, i0 = 0; i < sizeInBytes; i += 4, i0 += 2) {
             data[i0] = rgbaBytes[i];
             data[i0 + 1] = rgbaBytes[i + 1];
         }