paint_layer_clipper.h | Explore in Territory

/*
 * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
 * Copyright (C) 2013 Intel Corporation. All rights reserved.
 *
 * Portions are Copyright (C) 1998 Netscape Communications Corporation.
 *
 * Other contributors:
 *   Robert O'Callahan <[email protected]>
 *   David Baron <[email protected]>
 *   Christian Biesinger <[email protected]>
 *   Randall Jesup <[email protected]>
 *   Roland Mainz <[email protected]>
 *   Josh Soref <[email protected]>
 *   Boris Zbarsky <[email protected]>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of one of those two
 * licenses (the MPL or the GPL) and not to allow others to use your
 * version of this file under the LGPL, indicate your decision by
 * deletingthe provisions above and replace them with the notice and
 * other provisions required by the MPL or the GPL, as the case may be.
 * If you do not delete the provisions above, a recipient may use your
 * version of this file under any of the LGPL, the MPL or the GPL.
 */

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_CLIPPER_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_CLIPPER_H_

#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/layout/geometry/physical_offset.h"
#include "third_party/blink/renderer/core/layout/geometry/physical_rect.h"
#include "third_party/blink/renderer/platform/graphics/overlay_scrollbar_clip_behavior.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"

namespace blink {

class FragmentData;
class PaintLayer;

enum ShouldRespectOverflowClipType { … };

class ClipRectsContext { … };

// PaintLayerClipper is responsible for computing and caching clip
// rects.
//
// These clip rects have two types: background and foreground.
//
// The "background rect" for a PaintLayer is almost the same as its visual
// rect in the space of some ancestor PaintLayer (specified by rootLayer on
// ClipRectsContext).
// The only differences are that:
//   * The unclipped rect at the start is InfiniteIntRect(), rather than the
// local overflow bounds of the PaintLayer.
//   * CSS clip, the extent of visualOverflowRect(), and SVG root viewport
// clipping is applied.
// Thus, for example if there are no clips then the background rect will be
// infinite. Also, whether overflow clip of the ancestor should be applied is a
// parameter.
//
// The "foreground rect" for a PaintLayer is its "background rect", intersected
// with any clip applied by this PaintLayer to its children.

// Motivation for this class:
//
// 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.

class ClipRect;

class CORE_EXPORT PaintLayerClipper { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_PAINT_LAYER_CLIPPER_H_
chromium/third_party/blink/renderer/core/paint/paint_layer_clipper.h
