[Webkit-unassigned] [Bug 71595] [chromium] Add draw-time scale delta to compositor thread

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=71595





--- Comment #3 from Alexandre Elias <aelias at chromium.org>  2011-11-04 17:05:27 PST ---
Patch description:

Add draw-time scale delta to compositor thread.

- There are two magnify values:
1. The WebKit-side pageScale value corresponding to the resolution of
   the painted content.
2. The Impl-side-only scaleDelta value representing the additional
   degree of current magnification, applied as a draw transform.  WebKit is
   never explicitly aware of this value and the only way to change it
   currently is via pinch events (and in the future, double-tap/etc
   events).  At the end of a pinch zooms, we multiply pageScale *
   scaleDelta and tell WebKit to use it as the new pageScale.

- Scroll offsets and max-extents are maintained in pageScale space.
  When the scale changes, we need to take care to convert them to the
  new scale and avoid getting them clamped to the extents at the wrong
  scale.

- Remove maxScrollPosition on the non-impl side because it makes no
  sense to precompute it in the presence of an impl-side zoom.

- zoomAnimatorTransform is not used because it currently isn't in the
  branch, and mostly doesn't behave the way we want anyway (it does most
  things in WebKit thread).  We will need to unify these later.

- Also introduce deviceOrPageScaleFactorChanged() call which invalidates
  layers.

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