cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

cc/base/simple_enclosed_region.cc

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cc/base/simple_enclosed_region.h"
+
+#include "base/logging.h"
+#include "cc/base/region.h"
+
+namespace cc {
+
+static bool RectIsLargerArea(const gfx::Rect& a, const gfx::Rect b) {
+  int64 a_area = static_cast<int64>(a.width()) * a.height();
+  int64 b_area = static_cast<int64>(b.width()) * b.height();
+  return a_area > b_area;
+}
+
+SimpleEnclosedRegion::SimpleEnclosedRegion(const Region& region) {
+  for (Region::Iterator it(region); it.has_rect(); it.next())
+    Union(it.rect());
+}
+
+SimpleEnclosedRegion::~SimpleEnclosedRegion() {
+}
+
+void SimpleEnclosedRegion::Subtract(const gfx::Rect& sub_rect) {
+  // We want to keep as much of the current rect as we can, so find the one
+  // largest rectangle inside |rect_| that does not intersect with |sub_rect|.
+  if (!rect_.Intersects(sub_rect))
+    return;
+  if (sub_rect.Contains(rect_)) {
+    rect_ = gfx::Rect();
+    return;
+  }
+
+  int left = rect_.x();
+  int right = rect_.right();
+  int top = rect_.y();
+  int bottom = rect_.bottom();
+
+  int delta_left = sub_rect.x() - left;
+  int delta_right = right - sub_rect.right();
+  int delta_top = sub_rect.y() - top;
+  int delta_bottom = bottom - sub_rect.bottom();
+
+  // The horizontal rect is the larger of the two rectangles above or below
+  // |sub_rect| and inside rect_.
+  int horizontal_top = top;
+  int horizontal_bottom = bottom;
+  if (delta_top > delta_bottom)
+    horizontal_bottom = sub_rect.y();
+  else
+    horizontal_top = sub_rect.bottom();
+  // The vertical rect is the larger of the two rectangles to the left or the
+  // right of |sub_rect| and inside rect_.
+  int vertical_left = left;
+  int vertical_right = right;
+  if (delta_left > delta_right)
+    vertical_right = sub_rect.x();
+  else
+    vertical_left = sub_rect.right();
+
+  rect_.SetRect(
+      left, horizontal_top, right - left, horizontal_bottom - horizontal_top);
+
+  gfx::Rect vertical_rect(
+      vertical_left, top, vertical_right - vertical_left, bottom - top);
+  if (RectIsLargerArea(vertical_rect, rect_))
+    rect_ = vertical_rect;
+}
+
+void SimpleEnclosedRegion::Union(const gfx::Rect& new_rect) {
+  // We want to keep track of a region but bound its complexity at a constant
+  // size. We keep track of the largest rectangle seen by area. If we can add
+  // the |new_rect| to this rectangle then we do that, as that is the cheapest
+  // way to increase the area returned without increasing the complexity.
+  if (new_rect.IsEmpty())
+    return;
+  if (rect_.Contains(new_rect))
+    return;
+  if (new_rect.Contains(rect_)) {
+    rect_ = new_rect;
+    return;
+  }
+
+  int left = rect_.x();
+  int top = rect_.y();
+  int right = rect_.right();
+  int bottom = rect_.bottom();
+
+  int new_left = new_rect.x();
+  int new_top = new_rect.y();
+  int new_right = new_rect.right();
+  int new_bottom = new_rect.bottom();
+
+  // This attempts to expand each edge of |rect_| if the |new_rect| entirely
+  // covers or is adjacent to an entire edge of |rect_|. If this is true for
+  // an edge of |rect_| then it can be expanded out to share that edge with the
+  // same edge of |new_rect|. After, the same thing is done to try expand
+  // |new_rect| relative to |rect_|.
+  if (new_top <= top && new_bottom >= bottom) {
+    if (new_left < left && new_right >= left)
+      left = new_left;
+    if (new_right > right && new_left <= right)
+      right = new_right;
+  } else if (new_left <= left && new_right >= right) {
+    if (new_top < top && new_bottom >= top)
+      top = new_top;
+    if (new_bottom > bottom && new_top <= bottom)
+      bottom = new_bottom;
+  } else if (top <= new_top && bottom >= new_bottom) {
+    if (left < new_left && right >= new_left)
+      new_left = left;
+    if (right > new_right && left <= new_right)
+      new_right = right;
+  } else if (left <= new_left && right >= new_right) {
+    if (top < new_top && bottom >= new_top)
+      new_top = top;
+    if (bottom > new_bottom && top <= new_bottom)
+      new_bottom = bottom;
+  }
+
+  rect_.SetRect(left, top, right - left, bottom - top);
+
+  gfx::Rect adjusted_new_rect(
+      new_left, new_top, new_right - new_left, new_bottom - new_top);
+  if (RectIsLargerArea(adjusted_new_rect, rect_))
+    rect_ = adjusted_new_rect;
+}
+
+gfx::Rect SimpleEnclosedRegion::GetRect(size_t i) const {
+  DCHECK_LT(i, GetRegionComplexity());
+  return rect_;
+}
+
+}  // namespace cc