LibWeb: Make new ImageData() use unpremultiplied color data

This was already the case for `context.createImageData()`, but I forgot to do the same for `new ImageData()`. Add a regression test for both cases.
gmta · Aug 20, 2024 · 781a9f5 · 781a9f5
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diff --git a/Tests/LibWeb/Text/expected/HTML/canvas-putImageData-unpremultiplied.txt b/Tests/LibWeb/Text/expected/HTML/canvas-putImageData-unpremultiplied.txt
@@ -0,0 +1,2 @@
+PASS
+PASS
diff --git a/Tests/LibWeb/Text/input/HTML/canvas-putImageData-unpremultiplied.html b/Tests/LibWeb/Text/input/HTML/canvas-putImageData-unpremultiplied.html
@@ -0,0 +1,29 @@
+<script src="../include.js"></script>
+<body><canvas id=c width=1 height=2></div>
+<script>
+    test(() => {
+        // Test createImageData + putImageData
+        let ctx1 = c.getContext('2d');
+        let img1 = ctx1.createImageData(1, 1);
+        img1.data[0] = 50;
+        img1.data[1] = 100;
+        img1.data[2] = 200;
+        img1.data[3] = 0;
+        ctx1.putImageData(img1, 0, 0);
+        let buf1 = ctx1.getImageData(0, 0, 1, 1);
+        if (buf1.data[0] === 0 && buf1.data[1] === 0 && buf1.data[2] === 0 && buf1.data[3] === 0)
+            println("PASS");
+        else
+            println("FAIL");
+
+        // Test new ImageData + putImageData
+        let ctx2 = c.getContext('2d');
+        let img2 = new ImageData(new Uint8ClampedArray([50, 100, 200, 0]), 1, 1);
+        ctx2.putImageData(img2, 0, 0);
+        let buf2 = ctx2.getImageData(0, 0, 1, 1);
+        if (buf2.data[0] === 0 && buf2.data[1] === 0 && buf2.data[2] === 0 && buf2.data[3] === 0)
+            println("PASS");
+        else
+            println("FAIL");
+    });
+</script>
diff --git a/Userland/Libraries/LibWeb/HTML/ImageData.cpp b/Userland/Libraries/LibWeb/HTML/ImageData.cpp
@@ -74,7 +74,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<ImageData>> ImageData::create(JS::Realm& re
         return WebIDL::IndexSizeError::create(realm, "Source height must be equal to the calculated height of the data."_fly_string);
 
     // 7. Initialize this given sw, sh, settings set to settings, and source set to data.
-    auto bitmap = TRY_OR_THROW_OOM(vm, Gfx::Bitmap::create_wrapper(Gfx::BitmapFormat::RGBA8888, Gfx::AlphaType::Premultiplied, Gfx::IntSize(sw, height), sw * sizeof(u32), uint8_clamped_array_data.data().data()));
+    auto bitmap = TRY_OR_THROW_OOM(vm, Gfx::Bitmap::create_wrapper(Gfx::BitmapFormat::RGBA8888, Gfx::AlphaType::Unpremultiplied, Gfx::IntSize(sw, height), sw * sizeof(u32), uint8_clamped_array_data.data().data()));
 
     return realm.heap().allocate<ImageData>(realm, realm, bitmap, uint8_clamped_array_data);
 }