gecko/layout/reftests/position-dynamic-changes/multiple-changes-ref.html
Ehsan Akhgari 5682d40581 Bug 157681 - Part 2: Optimize positioned frame offset changes by moving the frame as opposed to reflowing it in case we know that the size of the frame will not change; r=dbaron
This patch adds a change hint to signal that one of the offsets on a
frame has been changed.  When processing the hint, we do one of the
following things based on the position property of the frame.

* For static frames, we ignore the offset changes completely, as they
  will not change the layout.
* For relative positioned frames, this patch refactors the
  nsHTMLReflowState::ComputeRelativeOffsets function so that it can be
  used from other callers, and it uses that to compute the new relative
  offsets, and uses the offsets computed previously to compute the new
  position of the frame.
* For absolute positioned frames, we set up a fake parent reflow state
  object, and then we create a new reflow state object for the frame in
  question.  This setup is similar to what nsFrame::BoxReflow does.
  Once we have the new reflow state object, we use it to compute the
  absolute offsets, and then we use the computed offsets to set the new
  position of the frame.  The offset computation is similar to what
  nsAbsoluteContainingBlock::ReflowAbsoluteFrame does.  In some cases
  where it is possible for the dimensions of the frame to change based
  on the offset changes, we fall back to a full reflow.
2012-06-06 00:53:48 -04:00

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HTML

<!DOCTYPE html>
<html>
<body>
<style>
#a { border: 1px solid black; width: 100px; height: 100px; left: 10px; }
#b { border: 1px solid blue; width: 50px; height: 50px; left: 20px; }
div { position: absolute; }
</style>
<div id="a">
<div id="b">
</div>
</div>
</body>
</html>