[Webkit-unassigned] [Bug 50865] New: GlyphPage::fill() is slow on vertical writing (Mac)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=50865

           Summary: GlyphPage::fill() is slow on vertical writing (Mac)
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: takano1 at asia.apple.com
                CC: hyatt at apple.com, adele at apple.com, mitz at webkit.org


On vertical writing, GlyphPage::fill() uses CoreText instead of CG to map characters into glyphs. The CoreText path is obviously complex and slow. When I sampled with natural Japanese text rendering, I saw it is almost 2.5 times slower than CG path (around 100 samples vs around 270 samples.)  We can improve the performance by using CG path on ideograph-only page even in vertical writing mode, as we know ideographs don't have a vertical variant glyph.

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