I experienced this when writing RenderMediaControlsChromium. I would create a rounded rectangle path the add it via addPath() then fill it via fillPath() with alpha blending. It rendered correctly, but mousing over/using scroll wheel on the page would cause the re-fill the area, creating a different appearance. I'm thinking context isn't being saved correctly or something.. I'll try and get a better repro steps.
This is happening in Skia because we only draw rounded borders when the rounding fits into the rectangle. See this code in Source/WebCore/platform/graphics/skia/GraphicsContextSkia.cpp : Function: void GraphicsContext::fillRoundedRect() if (topLeft.width() + topRight.width() > rect.width() || bottomLeft.width() + bottomRight.width() > rect.width() || topLeft.height() + bottomLeft.height() > rect.height() || topRight.height() + bottomRight.height() > rect.height()) { // Not all the radii fit, return a rect. This matches the behavior of // Path::createRoundedRectangle. Without this we attempt to draw a round // shadow for a square box. fillRect(rect, color, colorSpace); return; } Thus, when the volume slider is too close to 0% or to 100%, the rectangle gets too small to be able to draw the arcs. See bug https://bugs.webkit.org/show_bug.cgi?id=23882 . I don't quite know how to implement the rounded fillers now. Any suggestions?
Oh my I filed this bug back waaaaaaay back when I initially was working on the original controls :P Are you still hitting it?
I can actually get around this if I make the right side non-rounded underneath the slider thumbs. Also, I have to take the zoomFactor into account. Given all this, it might make sense to re-write this code by introducing a div for the background color and a div for the highlighted buffered range. I'll continue to try in C++ for now. :-)
I think we can close this - I have a patch for the video controls that works.