1 files changed, 279 insertions, 0 deletions
diff --git a/ppapi/utility/graphics/paint_aggregator.cc b/ppapi/utility/graphics/paint_aggregator.cc
new file mode 100644
index 0000000..d4fc721
--- /dev/null
+++ b/ppapi/utility/graphics/paint_aggregator.cc
@@ -0,0 +1,279 @@
+// Copyright (c) 2011 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 "ppapi/utility/graphics/paint_aggregator.h"
+
+#include <algorithm>
+
+#include "ppapi/cpp/logging.h"
+
+// ----------------------------------------------------------------------------
+// ALGORITHM NOTES
+//
+// We attempt to maintain a scroll rect in the presence of invalidations that
+// are contained within the scroll rect.  If an invalidation crosses a scroll
+// rect, then we just treat the scroll rect as an invalidation rect.
+//
+// For invalidations performed prior to scrolling and contained within the
+// scroll rect, we offset the invalidation rects to account for the fact that
+// the consumer will perform scrolling before painting.
+//
+// We only support scrolling along one axis at a time.  A diagonal scroll will
+// therefore be treated as an invalidation.
+// ----------------------------------------------------------------------------
+
+namespace pp {
+
+PaintAggregator::PaintUpdate::PaintUpdate() : has_scroll(false) {}
+
+PaintAggregator::PaintUpdate::~PaintUpdate() {}
+
+PaintAggregator::InternalPaintUpdate::InternalPaintUpdate() {}
+
+PaintAggregator::InternalPaintUpdate::~InternalPaintUpdate() {}
+
+Rect PaintAggregator::InternalPaintUpdate::GetScrollDamage() const {
+  // Should only be scrolling in one direction at a time.
+  PP_DCHECK(!(scroll_delta.x() && scroll_delta.y()));
+
+  Rect damaged_rect;
+
+  // Compute the region we will expose by scrolling, and paint that into a
+  // shared memory section.
+  if (scroll_delta.x()) {
+    int32_t dx = scroll_delta.x();
+    damaged_rect.set_y(scroll_rect.y());
+    damaged_rect.set_height(scroll_rect.height());
+    if (dx > 0) {
+      damaged_rect.set_x(scroll_rect.x());
+      damaged_rect.set_width(dx);
+    } else {
+      damaged_rect.set_x(scroll_rect.right() + dx);
+      damaged_rect.set_width(-dx);
+    }
+  } else {
+    int32_t dy = scroll_delta.y();
+    damaged_rect.set_x(scroll_rect.x());
+    damaged_rect.set_width(scroll_rect.width());
+    if (dy > 0) {
+      damaged_rect.set_y(scroll_rect.y());
+      damaged_rect.set_height(dy);
+    } else {
+      damaged_rect.set_y(scroll_rect.bottom() + dy);
+      damaged_rect.set_height(-dy);
+    }
+  }
+
+  // In case the scroll offset exceeds the width/height of the scroll rect
+  return scroll_rect.Intersect(damaged_rect);
+}
+
+Rect PaintAggregator::InternalPaintUpdate::GetPaintBounds() const {
+  Rect bounds;
+  for (size_t i = 0; i < paint_rects.size(); ++i)
+    bounds = bounds.Union(paint_rects[i]);
+  return bounds;
+}
+
+PaintAggregator::PaintAggregator()
+    : max_redundant_paint_to_scroll_area_(0.8f),
+      max_paint_rects_(10) {
+}
+
+bool PaintAggregator::HasPendingUpdate() const {
+  return !update_.scroll_rect.IsEmpty() || !update_.paint_rects.empty();
+}
+
+void PaintAggregator::ClearPendingUpdate() {
+  update_ = InternalPaintUpdate();
+}
+
+PaintAggregator::PaintUpdate PaintAggregator::GetPendingUpdate() const {
+  // Convert the internal paint update to the external one, which includes a
+  // bit more precomputed info for the caller.
+  PaintUpdate ret;
+  ret.scroll_delta = update_.scroll_delta;
+  ret.scroll_rect = update_.scroll_rect;
+  ret.has_scroll = ret.scroll_delta.x() != 0 || ret.scroll_delta.y() != 0;
+
+  ret.paint_rects.reserve(update_.paint_rects.size() + 1);
+  for (size_t i = 0; i < update_.paint_rects.size(); i++)
+    ret.paint_rects.push_back(update_.paint_rects[i]);
+
+  ret.paint_bounds = update_.GetPaintBounds();
+
+  // Also include the scroll damage (if any) in the paint rects.
+  if (ret.has_scroll) {
+    PP_Rect scroll_damage = update_.GetScrollDamage();
+    ret.paint_rects.push_back(scroll_damage);
+    ret.paint_bounds = ret.paint_bounds.Union(scroll_damage);
+  }
+
+  return ret;
+}
+
+void PaintAggregator::InvalidateRect(const Rect& rect) {
+  // Combine overlapping paints using smallest bounding box.
+  for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
+    const 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.
+      Rect combined_rect = existing_rect.Union(rect);
+      update_.paint_rects.erase(update_.paint_rects.begin() + i);
+      InvalidateRect(combined_rect);
+      return;
+    }
+  }
+
+  // Add a non-overlapping paint.
+  update_.paint_rects.push_back(rect);
+
+  // If the new paint overlaps with a scroll, then it forces an invalidation of
+  // the scroll.  If the new paint is contained by a scroll, then trim off the
+  // scroll damage to avoid redundant painting.
+  if (!update_.scroll_rect.IsEmpty()) {
+    if (ShouldInvalidateScrollRect(rect)) {
+      InvalidateScrollRect();
+    } else if (update_.scroll_rect.Contains(rect)) {
+      update_.paint_rects[update_.paint_rects.size() - 1] =
+          rect.Subtract(update_.GetScrollDamage());
+      if (update_.paint_rects[update_.paint_rects.size() - 1].IsEmpty())
+        update_.paint_rects.erase(update_.paint_rects.end() - 1);
+    }
+  }
+
+  if (update_.paint_rects.size() > max_paint_rects_)
+    CombinePaintRects();
+}
+
+void PaintAggregator::ScrollRect(const Rect& clip_rect, const Point& amount) {
+  // We only support scrolling along one axis at a time.
+  if (amount.x() != 0 && amount.y() != 0) {
+    InvalidateRect(clip_rect);
+    return;
+  }
+
+  // We can only scroll one rect at a time.
+  if (!update_.scroll_rect.IsEmpty() && update_.scroll_rect != clip_rect) {
+    InvalidateRect(clip_rect);
+    return;
+  }
+
+  // Again, we only support scrolling along one axis at a time.  Make sure this
+  // update doesn't scroll on a different axis than any existing one.
+  if ((amount.x() && update_.scroll_delta.y()) ||
+      (amount.y() && update_.scroll_delta.x())) {
+    InvalidateRect(clip_rect);
+    return;
+  }
+
+  // The scroll rect is new or isn't changing (though the scroll amount may
+  // be changing).
+  update_.scroll_rect = clip_rect;
+  update_.scroll_delta += amount;
+
+  // We might have just wiped out a pre-existing scroll.
+  if (update_.scroll_delta == Point()) {
+    update_.scroll_rect = Rect();
+    return;
+  }
+
+  // Adjust any contained paint rects and check for any overlapping paints.
+  for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
+    if (update_.scroll_rect.Contains(update_.paint_rects[i])) {
+      update_.paint_rects[i] = ScrollPaintRect(update_.paint_rects[i], amount);
+      // The rect may have been scrolled out of view.
+      if (update_.paint_rects[i].IsEmpty()) {
+        update_.paint_rects.erase(update_.paint_rects.begin() + i);
+        i--;
+      }
+    } else if (update_.scroll_rect.Intersects(update_.paint_rects[i])) {
+      InvalidateScrollRect();
+      return;
+    }
+  }
+
+  // If the new scroll overlaps too much with contained paint rects, then force
+  // an invalidation of the scroll.
+  if (ShouldInvalidateScrollRect(Rect()))
+    InvalidateScrollRect();
+}
+
+Rect PaintAggregator::ScrollPaintRect(const Rect& paint_rect,
+                                      const Point& amount) const {
+  Rect result = paint_rect;
+
+  result.Offset(amount);
+  result = update_.scroll_rect.Intersect(result);
+
+  // Subtract out the scroll damage rect to avoid redundant painting.
+  return result.Subtract(update_.GetScrollDamage());
+}
+
+bool PaintAggregator::ShouldInvalidateScrollRect(const Rect& rect) const {
+  if (!rect.IsEmpty()) {
+    if (!update_.scroll_rect.Intersects(rect))
+      return false;
+
+    if (!update_.scroll_rect.Contains(rect))
+      return true;
+  }
+
+  // Check if the combined area of all contained paint rects plus this new
+  // rect comes too close to the area of the scroll_rect.  If so, then we
+  // might as well invalidate the scroll rect.
+
+  int paint_area = rect.size().GetArea();
+  for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
+    const Rect& existing_rect = update_.paint_rects[i];
+    if (update_.scroll_rect.Contains(existing_rect))
+      paint_area += existing_rect.size().GetArea();
+  }
+  int scroll_area = update_.scroll_rect.size().GetArea();
+  if (float(paint_area) / float(scroll_area) > max_redundant_paint_to_scroll_area_)
+    return true;
+
+  return false;
+}
+
+void PaintAggregator::InvalidateScrollRect() {
+  Rect scroll_rect = update_.scroll_rect;
+  update_.scroll_rect = Rect();
+  update_.scroll_delta = Point();
+  InvalidateRect(scroll_rect);
+}
+
+void PaintAggregator::CombinePaintRects() {
+  // Combine paint rects down to at most two rects: one inside the scroll_rect
+  // and one outside the scroll_rect.  If there is no scroll_rect, then just
+  // use the smallest bounding box for all paint rects.
+  //
+  // NOTE: This is a fairly simple algorithm.  We could get fancier by only
+  // combining two rects to get us under the max_paint_rects limit, but if we
+  // reach this method then it means we're hitting a rare case, so there's no
+  // need to over-optimize it.
+  //
+  if (update_.scroll_rect.IsEmpty()) {
+    Rect bounds = update_.GetPaintBounds();
+    update_.paint_rects.clear();
+    update_.paint_rects.push_back(bounds);
+  } else {
+    Rect inner, outer;
+    for (size_t i = 0; i < update_.paint_rects.size(); ++i) {
+      const Rect& existing_rect = update_.paint_rects[i];
+      if (update_.scroll_rect.Contains(existing_rect)) {
+        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);
+  }
+}
+
+}  // namespace pp