[Webkit-unassigned] [Bug 40077] [Qt] Implement the simple font code path.

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Jun 2 12:55:52 PDT 2010


--- Comment #4 from Simon Hausmann <hausmann at webkit.org>  2010-06-02 12:55:50 PST ---
Some additional context for the others:

The "fast path" in WebKit is implemented by caching the character->glyph mappings and the glyph advances in WebKit.

Qt has similar caches, inside the platform specific font engines.

Our goal is to use the mechanism inside WebKit to distinguish between simple and complex text and then use some new APIs that Jocelyn added to Qt 4.7 to layout and draw simple text. For the layout an overload of QFontMetrics::width will do the straight conversion from characters to glyphs and return the sum of the advances - no shaping involved and a very flat call stack with stack allocations in the common case. For drawing the shaping is also skipped and using the existing caches the text is quickly converted to glyphs and then passed down to the paint engine.

With this compromise we hope to achieve the same performance with less overall memory usage by re-using existing Qt caches.

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