This is the result of an missing clear operation in the canvas used to store the text atlas.
Created attachment 159240 [details] Patch
Comment on attachment 159240 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=159240&action=review > Source/WebCore/platform/graphics/chromium/CompositorHUDFontAtlas.cpp:68 > atlasContext.setFillColor(Color(0, 0, 0, 0), ColorSpaceDeviceRGB); > - atlasContext.fillRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE)); > + atlasContext.clearRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE)); how is clearRect() different from fillRect() with color(0, 0, 0, 0) ? do you still want to set the fill color when calling clearRect()?
(In reply to comment #2) > (From update of attachment 159240 [details]) > View in context: https://bugs.webkit.org/attachment.cgi?id=159240&action=review > > > Source/WebCore/platform/graphics/chromium/CompositorHUDFontAtlas.cpp:68 > > atlasContext.setFillColor(Color(0, 0, 0, 0), ColorSpaceDeviceRGB); > > - atlasContext.fillRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE)); > > + atlasContext.clearRect(FloatRect(0, 0, ATLAS_SIZE, ATLAS_SIZE)); > > how is clearRect() different from fillRect() with color(0, 0, 0, 0) ? The default transfer mode for GC is "source-over" (essentially a blend with whatever was in the background) which means with fillRect we're drawing a transparent rect over whatever was already there, which has no effect. clearRect sets the transfer mode to clear which does the job. > > do you still want to set the fill color when calling clearRect()? It's used by the Skia code when setting the paint, so I assume that yes, it's needed. Presumably you could clear to any color.
Comment on attachment 159240 [details] Patch Clearing flags on attachment: 159240 Committed r125961: <http://trac.webkit.org/changeset/125961>
All reviewed patches have been landed. Closing bug.