gcl change rev

ppapi/cpp/paint_aggregator.cc

-// 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/cpp/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