implement the logic to set tile priorities based on current matrix

cc/picture_layer_tiling.cc

 // Copyright 2012 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/picture_layer_tiling.h"
+
+#include "cc/math_util.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/size_conversions.h"
 
+#include <algorithm>
+
+namespace {
+
+const double kMaxTimeToVisibleInSeconds = 1000.0;
+
+int manhattanDistance(const gfx::Rect& a, const gfx::Rect& b)
+{
+    gfx::Rect c = gfx::UnionRects(a, b);
+    int x = std::max(0, c.width() - a.width() - b.width() + 1);
+    int y = std::max(0, c.height() - a.height() - b.height() + 1);
+    return (x + y);
+}
+
+}
+
 namespace cc {
 
 scoped_ptr<PictureLayerTiling> PictureLayerTiling::Create(
     float contents_scale,
     gfx::Size tile_size) {
   return make_scoped_ptr(new PictureLayerTiling(contents_scale, tile_size));
 }
 
 scoped_ptr<PictureLayerTiling> PictureLayerTiling::Clone() const {
   return make_scoped_ptr(new PictureLayerTiling(*this));
@@ skipping 240 matching lines @@
   DCHECK_LE(texture_rect.right(), texture_size().width());
   DCHECK_LE(texture_rect.bottom(), texture_size().height());
 
   return texture_rect;
 }
 
 gfx::Size PictureLayerTiling::Iterator::texture_size() const {
   return tiling_->tiling_data_.max_texture_size();
 }
 
+void PictureLayerTiling::UpdateTilePriorities(
+    const gfx::Size& view_port,
+    float layer_content_scale,
+    const gfx::Transform& last_transform,
+    const gfx::Transform& current_transform,
+    double time_delta) {
+  gfx::Rect countent_rect = ContentRect();
+  if (countent_rect.IsEmpty())
+    return;
+
+  gfx::Rect view_rect(gfx::Point(), view_port);
+  int right = tiling_data_.TileXIndexFromSrcCoord(countent_rect.width() - 1);
+  int bottom = tiling_data_.TileYIndexFromSrcCoord(countent_rect.height() - 1);
+  for (int j = 0; j <= bottom; ++j) {
+    for (int i = 0; i <= right; ++i) {
+      gfx::Rect content_rect = tiling_data_.TileBounds(i, j);
+      gfx::Rect layer_content_rect = gfx::ToEnclosingRect(
+          gfx::ScaleRect(content_rect, layer_content_scale / contents_scale_));
+      gfx::Rect screen_rect = MathUtil::mapClippedRect(
+          current_transform, layer_content_rect);
+      gfx::Rect previous_rect = MathUtil::mapClippedRect(
+          last_transform, layer_content_rect);
+
+      TilePriority priority;

[epenner, 2012/11/30 19:29:31]

Sorry if this is annoying, but after looking at the code, I think
tile_priority.h/cc would be a nice place for most of the math bits eg.
static TilePriority TilePriority::CalculatePriority...
wdyt?

[qinmin, 2012/11/30 20:32:35]

Done, the math thingy are moved to TilePriority. And unittest also moved there

On 2012/11/30 19:29:31, epenner wrote:

+      priority.resolution = HIGH_RESOLUTION;
+      priority.time_to_visible_in_seconds = TimeForBoundsToIntersect(
+          previous_rect, screen_rect, time_delta, view_rect);
+
+      priority.distance_to_visible_in_pixels = manhattanDistance(screen_rect,
+                                                                 view_rect);
+      // TODO(qinmin): pass the correct tree to this function.
+      TileAt(i, j)->set_priority(ACTIVE_TREE, priority);
+    }
+  }
+}
+
+double PictureLayerTiling::TimeForBoundsToIntersect(gfx::Rect previous_bounds,
+                                                    gfx::Rect current_bounds,
+                                                    double time_delta,
+                                                    gfx::Rect target_bounds) {
+  if (current_bounds.Intersects(target_bounds))
+    return 0;
+
+  if (previous_bounds.Intersects(target_bounds) || time_delta == 0)
+    return kMaxTimeToVisibleInSeconds;
+
+  // As we are trying to solve the case of both scaling and scrolling, using
+  // a single coordinate with velocity is not enough. The logic here is to
+  // calculate the velocity for each edge. Then we calculate the time range that
+  // each edge will stay on the same side of the target bounds. If there is an
+  // overlap between these time ranges, the bounds must have intersect with
+  // each other during that period of time.
+  double velocity =
+      (current_bounds.right() - previous_bounds.right()) / time_delta;
+  PictureLayerTiling::Range range = TimeRangeValueLargerThanThreshold(
+      current_bounds.right(), target_bounds.x(), velocity);
+
+  velocity = (current_bounds.x() - previous_bounds.x()) / time_delta;
+  range = range.Intersects(TimeRangeValueLargerThanThreshold(
+      -current_bounds.x(), -target_bounds.right(), -velocity));
+
+
+  velocity = (current_bounds.y() - previous_bounds.y()) / time_delta;
+  range = range.Intersects(TimeRangeValueLargerThanThreshold(
+      -current_bounds.y(), -target_bounds.bottom(), -velocity));
+
+  velocity = (current_bounds.bottom() - previous_bounds.bottom()) / time_delta;
+  range = range.Intersects(TimeRangeValueLargerThanThreshold(
+      current_bounds.bottom(), target_bounds.y(), velocity));
+
+  return range.IsEmpty() ? kMaxTimeToVisibleInSeconds : range.start_;
+}
+
+PictureLayerTiling::Range PictureLayerTiling::TimeRangeValueLargerThanThreshold(
+    int value, int threshold, double velocity) {
+  double minimum_time = 0;
+  double maximum_time = kMaxTimeToVisibleInSeconds;
+
+  if (velocity > 0) {
+    if (value < threshold)
+      minimum_time = std::min(kMaxTimeToVisibleInSeconds,
+                              (threshold - value) / velocity);
+  } else if (velocity <= 0) {
+    if (value < threshold)
+      minimum_time = kMaxTimeToVisibleInSeconds;
+    else if (velocity != 0)
+      maximum_time = std::min(maximum_time, (threshold - value) / velocity);
+  }
+
+  return PictureLayerTiling::Range(minimum_time, maximum_time);
+}
+
+PictureLayerTiling::Range PictureLayerTiling::Range::Intersects(
+    const PictureLayerTiling::Range& other) {
+  start_ = std::max(start_, other.start_);
+  end_ = std::min(end_, other.end_);
+  return PictureLayerTiling::Range(start_, end_);
+}
+
+bool PictureLayerTiling::Range::IsEmpty() {
+  return start_ >= end_;
+}
+
 }  // namespace cc