Chromium Code Reviews Chromium Code Reviews
Issue 1327483003:
Add documentation to 2 DeprecatedPaintLayer objects (Closed)
Base URL: svn://svn.chromium.org/blink/trunk| Index: Source/core/paint/DeprecatedPaintLayerClipper.h |
| diff --git a/Source/core/paint/DeprecatedPaintLayerClipper.h b/Source/core/paint/DeprecatedPaintLayerClipper.h |
| index a0303716c08c6eb070bd53d13e5d246f8d256bca..e9f337755183548685c2d3caa91c7461b557c66e 100644 |
| --- a/Source/core/paint/DeprecatedPaintLayerClipper.h |
| +++ b/Source/core/paint/DeprecatedPaintLayerClipper.h |
| @@ -127,6 +127,50 @@ private: |
| ShouldRespectOverflowClip respectOverflowClipForViewport; |
| }; |
| +// DeprecatedPaintLayerClipper is responsible for caching clip rects. |
|
wkorman
2015/09/01 17:58:20
Worth adding a note for any class with 'Deprecated
mstensho (USE GERRIT)
2015/09/01 18:59:06
Calculating and caching, perhaps?
Julien - ping for review
2015/09/03 14:25:54
I have added, that should clarify the status of th
|
| +// |
| +// 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 |
|
wkorman
2015/09/01 17:58:20
The way this is written up makes it sound as if, i
Julien - ping for review
2015/09/03 14:25:54
I don't really have a definite answer to your ques
|
| +// a layout tree walk and cache them for painting. |
| class DeprecatedPaintLayerClipper { |
| DISALLOW_ALLOCATION(); |
| WTF_MAKE_NONCOPYABLE(DeprecatedPaintLayerClipper); |
