63075 2011-06-21 09:56:55 -0700 REGRESSION (r88978): Text inside form controls looks really awful on Windows XP 2011-06-22 09:12:27 -0700 1 1 1 Unclassified WebKit Layout and Rendering 528+ (Nightly build) PC Windows XP RESOLVED FIXED data:text/html,<input value=foo> InRadar, PlatformOnly, Regression P2 Normal --- 1 aroben webkit-unassigned adachan bweinstein jhoneycutt oldest_to_newest 424506 0 98001 aroben 2011-06-21 09:56:55 -0700 Created attachment 98001 screenshot To reproduce: 1. Go to data:text/html,<input value=foo> The text inside the text field has this horrible black fringing which makes it look too bold and chunky. See screenshot. 424517 1 aroben 2011-06-21 10:12:45 -0700 Looks like this was caused by r88978: http://trac.webkit.org/changeset/88978 424520 2 aroben 2011-06-21 10:13:40 -0700 <rdar://problem/9648113> 424541 3 aroben 2011-06-21 10:37:20 -0700 Other folks at Apple have failed to repro this on Windows 7, even though I can repro on XP. My guess is that there's a difference in GDI behavior between XP and 7 that's causing the difference. 424652 4 aroben 2011-06-21 12:12:48 -0700 The bug only occurs when subpixel antialiasing is enabled. Turning off ClearType, or setting Safari's font-smoothing preference to "Best for CRT", makes the bug go away. 425189 5 98164 aroben 2011-06-22 07:02:07 -0700 Created attachment 98164 Testcase This testcase has the nice property that the upper-left pixel has a different appearance when the bug occurs and when it does not occur. This makes it easy to inspect the memory for the page's bitmap to see what's going on. 425194 6 aroben 2011-06-22 07:09:38 -0700 I'm stepping through the code using the attached testcase. Before RenderThemeWin::paintTextField is called, the bitmap is filled with 0xffffffff. RenderThemeWin::paintTextField then fills the text field with 0x00ffffff. Note that the alpha channel has been changed to 0. Soon later, Font::drawGlyphs is called. At this point the first few pixels are: 0x08000808 0xff728080 0xff808080 0xff808080 The first pixel here is nearly-transparent nearly-black. The second pixel is opaque gray with the red channel darkened a little. The third and fourth pixels are opaque gray. Over on the UI process side, ::BitBlt does preserve the alpha channel, so these same pixels end up written into the page's BackingStore bitmap. But when the page is displayed on screen, the alpha channel will be ignored, so the nearly-transparent nearly-black pixel will just become a nearly-black pixel, causing the ugly appearance. 425200 7 aroben 2011-06-22 07:16:57 -0700 One potential fix is to change DrawingAreaImpl::createGraphicsContext to create a GraphicsContext that does not support alpha. I.e., change this: return adoptPtr(new GraphicsContext(bitmapDC, true)); to this: return adoptPtr(new GraphicsContext(bitmapDC, false)); Doing so gives the following pixel values: 0xffffebbf 0xff918080 0xff808080 0xff808080 You can see that the first two pixels have changed to be opaque nearly-white and opaque nearly-gray, which is much better than opaque nearly-black! 425201 8 aroben 2011-06-22 07:17:43 -0700 Making this change also does not reintroduce bug 62690. 425267 9 aroben 2011-06-22 08:52:13 -0700 Rolling out r88978 changes the behavior of RenderThemeWin::paintTextField so that the 0xffffffff pixels keep that value. DrawThemeBackground still fills the temporary bitmap inside the LocalWindowsContext with 0x00ffffff as before, but GraphicsContext::releaseWindowsContext ignores the alpha channel when blitting back into the original GraphicsContext, so opaque white is preserved. 425277 10 98180 aroben 2011-06-22 09:05:34 -0700 Created attachment 98180 Don't use an alpha channel when drawing the web page on Windows 425280 11 aroben 2011-06-22 09:12:27 -0700 Committed r89436: <http://trac.webkit.org/changeset/89436> 98001 2011-06-21 09:56:55 -0700 2011-06-21 09:56:55 -0700 screenshot screenshot.png image/png 2152 aroben iVBORw0KGgoAAAANSUhEUgAAAmYAAAAhCAMAAABEMJdFAAAAAXNSR0IArs4c6QAAAARnQU1BAACx jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAwBQTFRF AAAAAABFAABxRQAAcQAARUVFAEWFAEWXAHG7RZe7cZeXf525RZfhcbv/hkUAl0UAu3EA4ZdF4btx /7txl7uXl+H/u//hu////+GX//+74f/////h////AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA 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