cc/tile_priority.h

// 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.

#ifndef CC_TILE_PRIORITY_H_
#define CC_TILE_PRIORITY_H_

#include <limits>

#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "cc/picture_pile.h"
#include "ui/gfx/rect.h"
#include "ui/gfx/size.h"

namespace base {
class Value;
}

namespace cc {

enum WhichTree {
  // Note: these must be 0 and 1 because we index with them in various places,
  // e.g. in Tile::priority_.
  ACTIVE_TREE = 0,
  PENDING_TREE = 1,
  NUM_TREES = 2
  // Be sure to update WhichTreeAsValue when adding new fields.
};
scoped_ptr<base::Value> WhichTreeAsValue(
    WhichTree tree);

enum TileResolution {
  LOW_RESOLUTION = 0 ,
  HIGH_RESOLUTION = 1,
  NON_IDEAL_RESOLUTION = 2,
};

struct CC_EXPORT TilePriority {
  TilePriority()
     : is_live(false),
       resolution(NON_IDEAL_RESOLUTION),
       time_to_visible_in_seconds(std::numeric_limits<float>::max()),
       distance_to_visible_in_pixels(std::numeric_limits<float>::max()) {}

  TilePriority(
    TileResolution resolution,
    float time_to_visible_in_seconds,
    float distance_to_visible_in_pixels)
     : is_live(true),
       resolution(resolution),
       time_to_visible_in_seconds(time_to_visible_in_seconds),
       distance_to_visible_in_pixels(distance_to_visible_in_pixels) {}

  TilePriority(const TilePriority& active, const TilePriority& pending) {
    if (!pending.is_live) {
      if (!active.is_live) {
        is_live = false;
        return;
      }
      is_live = true;
      resolution = active.resolution;
      time_to_visible_in_seconds = active.time_to_visible_in_seconds;
      distance_to_visible_in_pixels = active.distance_to_visible_in_pixels;
      return;
    } else if (!active.is_live) {
      is_live = true;
      resolution = pending.resolution;
      time_to_visible_in_seconds = pending.time_to_visible_in_seconds;
      distance_to_visible_in_pixels = pending.distance_to_visible_in_pixels;
      return;
    }

    is_live = true;
    if (active.resolution == HIGH_RESOLUTION ||
        pending.resolution == HIGH_RESOLUTION)
      resolution = HIGH_RESOLUTION;
    else if (active.resolution == LOW_RESOLUTION ||
             pending.resolution == LOW_RESOLUTION)
      resolution = LOW_RESOLUTION;
    else
      resolution = NON_IDEAL_RESOLUTION;

    time_to_visible_in_seconds =
      std::min(active.time_to_visible_in_seconds,
               pending.time_to_visible_in_seconds);
    distance_to_visible_in_pixels =
      std::min(active.distance_to_visible_in_pixels,
               pending.distance_to_visible_in_pixels);
  }

  static const float kMaxTimeToVisibleInSeconds;
  static const float kMaxDistanceInContentSpace;

  static inline float manhattanDistance(const gfx::RectF& a, const gfx::RectF& b) {
    // Compute the union explicitly.
    gfx::RectF c = gfx::RectF(
        std::min(a.x(), b.x()),
        std::min(a.y(), b.y()),
        std::max(a.right(), b.right()) - std::min(a.x(), b.x()),
        std::max(a.bottom(), b.bottom()) - std::min(a.y(), b.y()));

    // Rects touching the edge of the screen should not be considered visible.
    // So we add 1 pixel here to avoid that situation.
    float x = std::max(0.0f, c.width() - a.width() - b.width() + 1.0f);
    float y = std::max(0.0f, c.height() - a.height() - b.height() + 1.0f);
    return (x + y);
  }

  // Calculate the time for the |current_bounds| to intersect with the
  // |target_bounds| given its previous location and time delta.
  // This function should work for both scaling and scrolling case.
  static float TimeForBoundsToIntersect(const gfx::RectF& previous_bounds,
                                        const gfx::RectF& current_bounds,
                                        float time_delta,
                                        const gfx::RectF& target_bounds);

  // If a tile is not live, then all other fields are invalid.
  bool is_live;
  TileResolution resolution;
  float time_to_visible_in_seconds;
  float distance_to_visible_in_pixels;
};

enum TileMemoryLimitPolicy {
  // Nothing.
  ALLOW_NOTHING,

  // You might be made visible, but you're not being interacted with.
  ALLOW_ABSOLUTE_MINIMUM, // Tall.

  // You're being interacted with, but we're low on memory.
  ALLOW_PREPAINT_ONLY, // Grande.

  // You're the only thing in town. Go crazy.
  ALLOW_ANYTHING, // Venti.

  // Be sure to update TreePriorityAsValue when adding new fields.
};
scoped_ptr<base::Value> TileMemoryLimitPolicyAsValue(
    TileMemoryLimitPolicy policy);

enum TreePriority {
  SAME_PRIORITY_FOR_BOTH_TREES,
  SMOOTHNESS_TAKES_PRIORITY,
  NEW_CONTENT_TAKES_PRIORITY

  // Be sure to update TreePriorityAsValue when adding new fields.
};
scoped_ptr<base::Value> TreePriorityAsValue(TreePriority prio);

class GlobalStateThatImpactsTilePriority {
 public:
  GlobalStateThatImpactsTilePriority()
    : memory_limit_policy(ALLOW_NOTHING)
    , memory_limit_in_bytes(0)
    , tree_priority(SAME_PRIORITY_FOR_BOTH_TREES) {
  }

  TileMemoryLimitPolicy memory_limit_policy;

  size_t memory_limit_in_bytes;

  TreePriority tree_priority;

  scoped_ptr<base::Value> AsValue() const;
};

}  // namespace cc

#endif  // CC_TILE_PRIORITY_H_