297706 2025-08-20 18:45:12 -0700 [TextureMapper] wrong drop-shadow position in high DPI 2025-08-23 06:53:50 -0700 1 1 1 Unclassified WebKit Platform WebKit Nightly Build Unspecified Unspecified NEW https://bugs.webkit.org/show_bug.cgi?id=218734 DoNotImportToRadar P2 Normal --- 1 fujii webkit-unassigned bugs-noreply oldest_to_newest 2137898 0 fujii 2025-08-20 18:45:12 -0700 [GTK] wrong drop-shadow position in high DPI ./Tools/Scripts/run-minibrowser --gtk --release LayoutTests/css3/filters/drop-shadow-current-color.html EXPECTED: you should see 8 square boxes ACTUAL: you see 4 rectangles GTK WebKitTestRunner works as expected. 2137945 1 fujii 2025-08-21 02:47:47 -0700 Disabling the AC mode work around the problem. I can see 8 boxes. But, worng color, this is another bug. WEBKIT_DISABLE_COMPOSITING_MODE=1 ./Tools/Scripts/run-minibrowser --gtk --release LayoutTests/css3/filters/drop-shadow-current-color.html 2137956 2 476470 fujii 2025-08-21 04:32:52 -0700 Created attachment 476470 test case 2137962 3 fujii 2025-08-21 05:08:00 -0700 TextureMapper expects DIP (device independent pixel). But, GraphicsLayerCoordinated uses DP (device pixel). For example, there is 100px x 100px element in x2 device scale factor. GraphicsLayerTextureMapper and GraphicsLayerWC creates a 100x100 TextureMapperLayer. And, apply x2 scale transform to the root layer. OTOH, GraphicsLayerCoordinated creates a 200x200 TextureMapperLayer. TextureMapper::applyDropShadowFilter apply the drop-shadow filter. https://github.com/WebKit/WebKit/blob/5701312dba4c15a1c46bf57662d1638eda398100/Source/WebCore/platform/graphics/texmap/TextureMapper.cpp#L1064 LayerTreeHost::applyDeviceScaleFactor and DrawingAreaWC::updateRootLayerDeviceScaleFactor apply a transform to the root layer. https://github.com/WebKit/WebKit/blob/5701312dba4c15a1c46bf57662d1638eda398100/Source/WebKit/WebProcess/WebPage/CoordinatedGraphics/LayerTreeHostTextureMapper.cpp#L295 https://github.com/WebKit/WebKit/blob/5701312dba4c15a1c46bf57662d1638eda398100/Source/WebKit/WebProcess/WebPage/wc/DrawingAreaWC.cpp#L309 2138225 4 fujii 2025-08-22 05:26:24 -0700 I was wrong. GraphicsLayerCoordinated is using DIP. 2138456 5 fujii 2025-08-23 06:03:50 -0700 I confirmed Windows port has the same issue. This is a bug of TextureMapper. 2138462 6 fujii 2025-08-23 06:53:50 -0700 I think this is a the same problem with bug#218734. 476470 2025-08-21 04:32:52 -0700 2025-08-21 04:32:52 -0700 test case drop-shadow.html text/html 347 fujii PCFET0NUWVBFIGh0bWw+CjxzdHlsZT4KICBkaXYgewogICAgICBwb3NpdGlvbjogcmVsYXRpdmU7 CiAgICAgIG1hcmdpbjogMTBweDsKICAgICAgaGVpZ2h0OiAxMDBweDsKICAgICAgd2lkdGg6IDEw MHB4OwogIH0KICAuYiB7CiAgICAgIGJhY2tncm91bmQ6IGJsYWNrOwogICAgICBmaWx0ZXI6IGRy b3Atc2hhZG93KDExMHB4IDUwcHggMCBibGFjayk7CiAgfQogIC50IHsKICAgICAgd2lsbC1jaGFu Z2U6IHRyYW5zZm9ybTsKICB9Cjwvc3R5bGU+CllvdSBzaG91bGQgc2VlIDIgc3F1aXJlIGJveGVz IHdpdGhvdXQgYW4gaW50ZXJzZWN0aW9uIGluIGhpZ2ggRFBJLgo8ZGl2IGNsYXNzPSJiIHQiPjwv ZGl2Pgo=