| Index: Source/core/paint/DeprecatedPaintLayerClipper.h
|
| diff --git a/Source/core/paint/DeprecatedPaintLayerClipper.h b/Source/core/paint/DeprecatedPaintLayerClipper.h
|
| index 4f64cd0ebe2321300bb611e18aeef89f3512f637..7cb70bcbf68dfe1df5e98cecfa2cf8a13ab64ec1 100644
|
| --- a/Source/core/paint/DeprecatedPaintLayerClipper.h
|
| +++ b/Source/core/paint/DeprecatedPaintLayerClipper.h
|
| @@ -107,6 +107,54 @@ private:
|
| ShouldRespectOverflowClip respectOverflowClipForViewport;
|
| };
|
|
|
| +// DeprecatedPaintLayerClipper is responsible for computing and caching clip
|
| +// rects.
|
| +//
|
| +// The main reason for this cache is that we compute the clip rects during
|
| +// a layout tree walk but need them during a paint tree walk (see example
|
| +// below for some explanations).
|
| +//
|
| +// A lot of complexity in this class come from the difference in inheritance
|
| +// between 'overflow' and 'clip':
|
| +// * 'overflow' applies based on the containing blocks chain.
|
| +// (http://www.w3.org/TR/CSS2/visufx.html#propdef-overflow)
|
| +// * 'clip' applies to all descendants.
|
| +// (http://www.w3.org/TR/CSS2/visufx.html#propdef-clip)
|
| +//
|
| +// Let's take an example:
|
| +// <!DOCTYPE html>
|
| +// <div id="container" style="position: absolute; height: 100px; width: 100px">
|
| +// <div id="inflow" style="height: 200px; width: 200px;
|
| +// background-color: purple"></div>
|
| +// <div id="fixed" style="height: 200px; width: 200px; position: fixed;
|
| +// background-color: orange"></div>
|
| +// </div>
|
| +//
|
| +// The paint tree looks like:
|
| +// html
|
| +// / |
|
| +// / |
|
| +// / |
|
| +// container fixed
|
| +// |
|
| +// |
|
| +// inflow
|
| +//
|
| +// If we add "overflow: hidden" to #container, the overflow clip will apply to
|
| +// #inflow but not to #fixed. That's because #fixed's containing block is above
|
| +// #container and thus 'overflow' doesn't apply to it. During our tree walk,
|
| +// #fixed is a child of #container, which is the reason why we keep 3 clip rects
|
| +// depending on the 'position' of the elements.
|
| +//
|
| +// Now instead if we add "clip: rect(0px, 100px, 100px, 0px)" to #container,
|
| +// the clip will apply to both #inflow and #fixed. That's because 'clip'
|
| +// applies to any descendant, regardless of containing blocks. Note that
|
| +// #container and #fixed are siblings in the paint tree but #container does
|
| +// clip #fixed. This is the reason why we compute the painting clip rects during
|
| +// a layout tree walk and cache them for painting.
|
| +//
|
| +// This class is NOT DEPRECATED, DeprecatedPaintLayer is and we match its
|
| +// naming.
|
| class DeprecatedPaintLayerClipper {
|
| DISALLOW_ALLOCATION();
|
| WTF_MAKE_NONCOPYABLE(DeprecatedPaintLayerClipper);
|
|
|
Chromium Code Reviews
Issue 1327483003:
Add documentation to 2 DeprecatedPaintLayer objects (Closed)
Base URL: svn://svn.chromium.org/blink/trunk