Allow painting multiple paint rects....

chrome/renderer/paint_aggregator.cc

 // Copyright (c) 2009 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 "chrome/renderer/paint_aggregator.h"
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 
 // ----------------------------------------------------------------------------
@@ skipping 16 matching lines @@
 // This constant sets the max ratio of paint rect area to scroll rect area that
 // we will tolerate before dograding the scroll into a repaint.
 static const float kMaxRedundantPaintToScrollArea = 0.8f;
 
 // The maximum number of paint rects.  If we exceed this limit, then we'll
 // start combining paint rects (see CombinePaintRects).  This limiting is
 // important since the WebKit code associated with deciding what to paint given
 // a paint rect can be significant.
 static const size_t kMaxPaintRects = 5;
 
+// If the combined area of paint rects divided by the area of the union of all
+// paint rects exceeds this threshold, then we will combine the paint rects.
+static const float kMaxPaintRectsAreaRatio = 0.3f;
+
 PaintAggregator::PendingUpdate::PendingUpdate() {}
 
 PaintAggregator::PendingUpdate::~PendingUpdate() {}
 
 gfx::Rect PaintAggregator::PendingUpdate::GetScrollDamage() const {
   // Should only be scrolling in one direction at a time.
   DCHECK(!(scroll_delta.x() && scroll_delta.y()));
 
   gfx::Rect damaged_rect;
 
@@ skipping 35 matching lines @@
 }
 
 bool PaintAggregator::HasPendingUpdate() const {
   return !update_.scroll_rect.IsEmpty() || !update_.paint_rects.empty();
 }
 
 void PaintAggregator::ClearPendingUpdate() {
   update_ = PendingUpdate();
 }
 
+void PaintAggregator::PopPendingUpdate(PendingUpdate* update) {
+  // Combine paint rects if their combined area is not sufficiently less than
+  // the area of the union of all paint rects.  We skip this if there is a
+  // scroll rect since scrolling benefits from smaller paint rects.
+  if (update_.scroll_rect.IsEmpty() && update_.paint_rects.size() > 1) {
+    int paint_area = 0;
+    gfx::Rect union_rect;
+    for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
+      paint_area += update_.paint_rects[i].size().GetArea();
+      union_rect = union_rect.Union(update_.paint_rects[i]);
+    }
+    int union_area = union_rect.size().GetArea();
+    if (float(paint_area) / float(union_area) > kMaxPaintRectsAreaRatio)
+      CombinePaintRects();
+  }
+  *update = update_;
+  ClearPendingUpdate();
+}
+
 void PaintAggregator::InvalidateRect(const gfx::Rect& rect) {
   // Combine overlapping paints using smallest bounding box.
   for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
     const gfx::Rect& existing_rect = update_.paint_rects[i];
     if (existing_rect.Contains(rect))  // Optimize out redundancy.
       return;
     if (rect.Intersects(existing_rect) || rect.SharesEdgeWith(existing_rect)) {
       // Re-invalidate in case the union intersects other paint rects.
       gfx::Rect combined_rect = existing_rect.Union(rect);
       update_.paint_rects.erase(update_.paint_rects.begin() + i);
@@ skipping 18 matching lines @@
         update_.paint_rects.erase(update_.paint_rects.end() - 1);
     }
   }
 
   if (update_.paint_rects.size() > kMaxPaintRects)
     CombinePaintRects();
 
   // Track how large the paint_rects vector grows during an invalidation
   // sequence.  Note: A subsequent invalidation may end up being combined
   // with all existing paints, which means that tracking the size of
-  // paint_rects at the time when GetPendingUpdate() is called may mask
+  // paint_rects at the time when PopPendingUpdate() is called may mask
   // certain performance problems.
   HISTOGRAM_COUNTS_100("MPArch.RW_IntermediatePaintRectCount",
                        update_.paint_rects.size());
 }
 
 void PaintAggregator::ScrollRect(int dx, int dy, const gfx::Rect& clip_rect) {
   // We only support scrolling along one axis at a time.
   if (dx != 0 && dy != 0) {
     InvalidateRect(clip_rect);
     return;
@@ skipping 111 matching lines @@
         inner = inner.Union(existing_rect);
       } else {
         outer = outer.Union(existing_rect);
       }
     }
     update_.paint_rects.clear();
     update_.paint_rects.push_back(inner);
     update_.paint_rects.push_back(outer);
   }
 }