[Webkit-unassigned] [Bug 227912] New: Back to front buffer copies in scaled image buffers should not hit the sub image code path

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=227912

            Bug ID: 227912
           Summary: Back to front buffer copies in scaled image buffers
                    should not hit the sub image code path
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: simon.fraser at apple.com

Because of integral sizing of image buffers with fractional scales, we end up hitting the sub image code path here:

  * frame #0: 0x00000001efff61ca WebCore`WebCore::GraphicsContextCG::drawNativeImage(this=0x0000000239dde1a8, nativeImage=0x0000000232bab0c0, imageSize={ width = 1259.0, height = 142.0 }, destRect={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, srcRect={ x = 0.0, y = 0.0, width = 1258.32007, height = 141.240005 }, options=0x00007ffee5548f80) at GraphicsContextCG.cpp:309:5
    frame #1: 0x00000001f000c3c6 WebCore`WebCore::ImageBufferCGBackend::draw(this=0x000000023c3142a0, destContext=0x0000000239dde1a8, destRect={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, srcRect={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, options=0x00007ffee5548f80) at ImageBufferCGBackend.cpp:141:21
    frame #2: 0x00000001c8b688e2 WebKit`WebCore::ConcreteImageBuffer<WebKit::ImageBufferShareableMappedIOSurfaceBackend>::draw(this=0x0000000231eba550, destContext=0x0000000239dde1a8, destRect={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, srcRect={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, options=0x00007ffee5548f80) at ConcreteImageBuffer.h:144:22
    frame #3: 0x00000001efef9541 WebCore`WebCore::GraphicsContext::drawImageBuffer(this=0x0000000239dde1a8, image=0x0000000231eba550, destination={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, source={ x = 0.0, y = 0.0, width = 392.0, height = 44.0 }, options=0x00007ffee5548f80) at GraphicsContext.cpp:579:11
    frame #4: 0x00000001c8e4d22b WebKit`WebKit::RemoteLayerBackingStore::display(this=0x0000000220d39ea0) at RemoteLayerBackingStore.mm:302:17
    frame #5: 0x00000001c9fe27ed WebKit`WebKit::PlatformCALayerRemote::recursiveBuildTransaction(this=0x0000000232b61240, context=0x0000000220da32f0, transaction=0x00007ffee55499f8) at PlatformCALayerRemote.cpp:181:102


This is a waste of cycles; we never want to hit the sub image cache for these copies, and we know we can just splat the whole buffer over.

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