Bug 157665 – cross-fade() rendering doesn't match expectation

• Status: RESOLVED
• Resolution: FIXED
• Component: CSS

[Simon Fraser (smfr)]

The result of LayoutTests/css3/images/cross-fade-blending.html no longer matches the expected PNG file.

It seems that at intermediate stages of the blend, blending between two opaque images gives a non-opaque result, which is not what should happen.

Sadly cross-fade doesn't have any reference tests that would have caught this regression.

[Simon Fraser (smfr)]

Created attachment 278818 [details]
Screenshot

[Simon Fraser (smfr)]

Crossfade draws with:

    context.beginTransparencyLayer(1);

    drawCrossfadeSubimage(context, m_fromImage.get(), CompositeSourceOver, 1 - m_percentage, m_crossfadeSize);
    drawCrossfadeSubimage(context, m_toImage.get(), CompositePlusLighter, m_percentage, m_crossfadeSize);

    context.endTransparencyLayer();

which I would expect to work, unless it fails because of non-linear gamma?

It works correctly if we always go down the "useTransparencyLayer" code path.

[Simon Fraser (smfr)]

We're dropping the blend mode on the floor (but need to fix the transparency layer case).

Probably regressed in r157045.

diff --git a/Source/WebCore/platform/graphics/CrossfadeGeneratedImage.cpp b/Source/WebCore/platform/graphics/CrossfadeGeneratedImage.cpp
index 57e3f1a4f1906a2669ffffdd201559cb3eb5ca16..4acfd8ad22800cf2173f1dab8a79f54c8f9092fc 100644
--- a/Source/WebCore/platform/graphics/CrossfadeGeneratedImage.cpp
+++ b/Source/WebCore/platform/graphics/CrossfadeGeneratedImage.cpp
@@ -51,7 +51,7 @@ static void drawCrossfadeSubimage(GraphicsContext& context, Image& image, Compos
 
     GraphicsContextStateSaver stateSaver(context);
 
-    context.setCompositeOperation(operation);
+//    context.setCompositeOperation(operation);
 
     if (useTransparencyLayer)
         context.beginTransparencyLayer(opacity);
@@ -60,7 +60,7 @@ static void drawCrossfadeSubimage(GraphicsContext& context, Image& image, Compos
 
     if (targetSize != imageSize)
         context.scale(FloatSize(targetSize.width() / imageSize.width(), targetSize.height() / imageSize.height()));
-    context.drawImage(image, IntPoint());
+    context.drawImage(image, IntPoint(), ImagePaintingOptions(operation));
 
     if (useTransparencyLayer)
         context.endTransparencyLayer();

[Simon Fraser (smfr)]

Created attachment 278869 [details]
Patch

[Build Bot]

Comment on attachment 278869 [details]
Patch

Attachment 278869 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.webkit.org/results/1316744

Number of test failures exceeded the failure limit.

[Build Bot]

Created attachment 278872 [details]
Archive of layout-test-results from ews102 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews102  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Simon Fraser (smfr)]

Created attachment 278873 [details]
Patch

[Simon Fraser (smfr)]

rdar://problem/17917708

[Build Bot]

Comment on attachment 278873 [details]
Patch

Attachment 278873 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.webkit.org/results/1316839

New failing tests:
css3/images/cross-fade-blending.html

[Build Bot]

Created attachment 278875 [details]
Archive of layout-test-results from ews101 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews101  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 278869 [details]
Patch

Attachment 278869 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/1316835

New failing tests:
css3/images/cross-fade-blending.html

[Build Bot]

Created attachment 278876 [details]
Archive of layout-test-results from ews107 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews107  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 278869 [details]
Patch

Attachment 278869 [details] did not pass ios-sim-ews (ios-simulator-wk2):
Output: http://webkit-queues.webkit.org/results/1316831

New failing tests:
css3/images/cross-fade-blending.html

[Build Bot]

Created attachment 278880 [details]
Archive of layout-test-results from ews121 for ios-simulator-wk2

The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews121  Port: ios-simulator-wk2  Platform: Mac OS X 10.11.4

[Simon Fraser (smfr)]

https://trac.webkit.org/r200889