[Webkit-unassigned] [Bug 31258] New: Win chromium is slow to draw transparent texts

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=31258

           Summary: Win chromium is slow to draw transparent texts
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
               URL: http://handcraftedcss.com/workshop/
        OS/Version: Windows XP
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: hamaji at chromium.org
                CC: brettw at chromium.org


Created an attachment (id=42755)
 --> (https://bugs.webkit.org/attachment.cgi?id=42755)
reduction

Scrolling in the posted URL is very slow with Windows Chromium. This doesn't
happen in other environments.

sunandt found that fixed background and rgba text causes this issue, and I
noticed this issue happens with rgba text. With the attached HTML which doesn't
have background, page up/down is still slow. Scrolling with mouse or arrow keys
are OK because we can optimize scrolling with blit for this case (as background
prevents this optimization, the original URL was slow even for mouse and arrow
keys).

It seems TransparencyAwareFontPainter in FontChromiumWin.cpp is the reason of
this slowness. It seems the graphics context isn't clipped properly when GDI is
used.

I'll post a patch for this, but I'm not sure if the fix is good as I don't have
enough knowledges about this code. Any suggestions will be appreciated.

Chromium side bug: http://code.google.com/p/chromium/issues/detail?id=18537

-- 
Configure bugmail: https://bugs.webkit.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the assignee for the bug.