src/cobalt/renderer/rasterizer/egl/offscreen_target_manager.cc

// Copyright 2017 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "cobalt/renderer/rasterizer/egl/offscreen_target_manager.h"

#include <algorithm>

#include "base/hash_tables.h"
#include "cobalt/renderer/rasterizer/egl/rect_allocator.h"
#include "third_party/skia/include/core/SkRefCnt.h"

namespace {
// Structure describing the key for render target allocations in a given
// offscreen target atlas.
struct AllocationKey {
  AllocationKey(const cobalt::render_tree::Node* tree_node,
                const cobalt::math::SizeF& alloc_size)
      : node(tree_node),
        size(alloc_size) {}

  bool operator==(const AllocationKey& other) const {
    return node == other.node && size == other.size;
  }

  bool operator!=(const AllocationKey& other) const {
    return node != other.node || size != other.size;
  }

  bool operator<(const AllocationKey& rhs) const {
    return (node < rhs.node) ||
           (node == rhs.node &&
               (size.width() < rhs.size.width() ||
               (size.width() == rhs.size.width() &&
                   size.height() < rhs.size.height())));
  }

  const void* node;
  cobalt::math::SizeF size;
};
}  // namespace

namespace BASE_HASH_NAMESPACE {
#if defined(BASE_HASH_USE_HASH_STRUCT)
template <>
struct hash<AllocationKey> {
  size_t operator()(const AllocationKey& key) const {
    return reinterpret_cast<size_t>(key.node);
  }
};
#else
template <>
inline size_t hash_value<AllocationKey>(const AllocationKey& key) {
  return reinterpret_cast<size_t>(key.node);
}
#endif
}  // namespace BASE_HASH_NAMESPACE

namespace cobalt {
namespace renderer {
namespace rasterizer {
namespace egl {

namespace {

typedef base::hash_map<AllocationKey, math::Rect> AllocationMap;

int32_t NextPowerOf2(int32_t num) {
  // Return the smallest power of 2 that is greater than or equal to num.
  // This flips on all bits <= num, then num+1 will be the next power of 2.
  --num;
  num |= num >> 1;
  num |= num >> 2;
  num |= num >> 4;
  num |= num >> 8;
  num |= num >> 16;
  return num + 1;
}

bool IsPowerOf2(int32_t num) {
  return (num & (num - 1)) == 0;
}

size_t GetMemorySize(const math::Size& target_size) {
  // RGBA uses 4 bytes per pixel. Assume no rounding to the nearest power of 2.
  return target_size.width() * target_size.height() * 4;
}

}  // namespace

struct OffscreenTargetManager::OffscreenAtlas {
  explicit OffscreenAtlas(const math::Size& size)
      : allocator(size),
        allocations_used(0),
        needs_flush(false) {}

  RectAllocator allocator;
  AllocationMap allocation_map;
  size_t allocations_used;
  scoped_refptr<backend::FramebufferRenderTargetEGL> framebuffer;
  SkAutoTUnref<SkSurface> skia_surface;
  bool needs_flush;
};

OffscreenTargetManager::OffscreenTargetManager(
    backend::GraphicsContextEGL* graphics_context,
    const CreateFallbackSurfaceFunction& create_fallback_surface,
    size_t memory_limit)
    : graphics_context_(graphics_context),
      create_fallback_surface_(create_fallback_surface),
      offscreen_target_size_mask_(0, 0),
      memory_limit_(memory_limit) {
}

OffscreenTargetManager::~OffscreenTargetManager() {
}

void OffscreenTargetManager::Update(const math::Size& frame_size) {
  if (offscreen_atlases_.empty()) {
    InitializeTargets(frame_size);
  }

  // If any of the current atlases have more allocations used than the
  // current cache, then use that as the new cache.
  size_t most_used_atlas_index = 0;
  for (size_t index = 1; index < offscreen_atlases_.size(); ++index) {
    if (offscreen_atlases_[most_used_atlas_index]->allocations_used <
        offscreen_atlases_[index]->allocations_used) {
      most_used_atlas_index = index;
    }
  }

  OffscreenAtlas* most_used_atlas = offscreen_atlases_[most_used_atlas_index];
  if (offscreen_cache_->allocations_used < most_used_atlas->allocations_used) {
    OffscreenAtlas* new_atlas = offscreen_cache_.release();
    offscreen_cache_.reset(offscreen_atlases_[most_used_atlas_index]);
    offscreen_atlases_.weak_erase(offscreen_atlases_.begin() +
                                  most_used_atlas_index);
    offscreen_atlases_.push_back(new_atlas);
  }
  offscreen_cache_->allocations_used = 0;

  // Reset all current atlases for use this frame.
  for (size_t index = 0; index < offscreen_atlases_.size(); ++index) {
    OffscreenAtlas* atlas = offscreen_atlases_[index];
    atlas->allocator.Reset();
    atlas->allocation_map.clear();
    atlas->allocations_used = 0;
  }
}

void OffscreenTargetManager::Flush() {
  if (offscreen_cache_->needs_flush) {
    offscreen_cache_->needs_flush = false;
    offscreen_cache_->skia_surface->getCanvas()->flush();
  }
  for (size_t index = 0; index < offscreen_atlases_.size(); ++index) {
    if (offscreen_atlases_[index]->needs_flush) {
      offscreen_atlases_[index]->needs_flush = false;
      offscreen_atlases_[index]->skia_surface->getCanvas()->flush();
    }
  }
}

bool OffscreenTargetManager::GetCachedOffscreenTarget(
    const render_tree::Node* node, const math::SizeF& size,
    TargetInfo* out_target_info) {
  AllocationMap::iterator iter = offscreen_cache_->allocation_map.find(
      AllocationKey(node, size));
  if (iter != offscreen_cache_->allocation_map.end()) {
    offscreen_cache_->allocations_used += 1;
    out_target_info->framebuffer = offscreen_cache_->framebuffer.get();
    out_target_info->skia_canvas = offscreen_cache_->skia_surface->getCanvas();
    out_target_info->region = iter->second;
    return true;
  }
  return false;
}

void OffscreenTargetManager::AllocateOffscreenTarget(
    const render_tree::Node* node, const math::SizeF& size,
    TargetInfo* out_target_info) {
  // Pad the offscreen target size to prevent interpolation with unwanted
  // texels when rendering the results.
  const int kInterpolatePad = 1;

  // Get an offscreen target for rendering. Align up the requested target size
  // to improve usage of the atlas (since more requests will have the same
  // aligned width or height).
  DCHECK(IsPowerOf2(offscreen_target_size_mask_.width() + 1));
  DCHECK(IsPowerOf2(offscreen_target_size_mask_.height() + 1));
  math::Size target_size(
      (static_cast<int>(size.width()) + 2 * kInterpolatePad +
          offscreen_target_size_mask_.width()) &
          ~offscreen_target_size_mask_.width(),
      (static_cast<int>(size.height()) + 2 * kInterpolatePad +
          offscreen_target_size_mask_.height()) &
          ~offscreen_target_size_mask_.height());
  math::Rect target_rect(0, 0, 0, 0);
  OffscreenAtlas* atlas = NULL;

  // See if there's room in the offscreen cache for additional targets.
  atlas = offscreen_cache_.get();
  target_rect = atlas->allocator.Allocate(target_size);

  if (target_rect.IsEmpty()) {
    // See if there's room in the other atlases.
    for (size_t index = offscreen_atlases_.size(); index > 0;) {
      atlas = offscreen_atlases_[--index];
      target_rect = atlas->allocator.Allocate(target_size);
      if (!target_rect.IsEmpty()) {
        break;
      }
    }
  }

  if (target_rect.IsEmpty()) {
    // There wasn't enough room for the requested offscreen target.
    out_target_info->framebuffer = nullptr;
    out_target_info->skia_canvas = nullptr;
    out_target_info->region.SetRect(0, 0, 0, 0);
  } else {
    // Inset to prevent interpolation with unwanted pixels at the edge.
    target_rect.Inset(kInterpolatePad, kInterpolatePad);

    // Clear the atlas if this will be the first draw into it.
    if (atlas->allocation_map.empty()) {
      atlas->skia_surface->getCanvas()->clear(SK_ColorTRANSPARENT);
    }

    atlas->allocation_map.insert(AllocationMap::value_type(
        AllocationKey(node, size), target_rect));
    atlas->allocations_used += 1;
    atlas->needs_flush = true;

    out_target_info->framebuffer = atlas->framebuffer.get();
    out_target_info->skia_canvas = atlas->skia_surface->getCanvas();
    out_target_info->region = target_rect;
  }
}

void OffscreenTargetManager::InitializeTargets(const math::Size& frame_size) {
  DLOG(INFO) << "offscreen render target memory limit: " << memory_limit_;

  if (frame_size.width() >= 64 && frame_size.height() >= 64) {
    offscreen_target_size_mask_.SetSize(
        NextPowerOf2(frame_size.width() / 64) - 1,
        NextPowerOf2(frame_size.height() / 64) - 1);
  } else {
    offscreen_target_size_mask_.SetSize(0, 0);
  }

  // Allow offscreen targets to be as large as the frame.
  math::Size max_size(std::max(frame_size.width(), 1),
                      std::max(frame_size.height(), 1));

  // Offscreen render targets are optional but highly recommended. These
  // allow caching of render results for improved performance. At least two
  // must exist -- one for the cache and the other a working scratch.
  size_t half_memory_limit = memory_limit_ / 2;
  math::Size atlas_size(1, 1);
  for (;;) {
    // See if the next atlas size will fit in the memory budget.
    // Try to keep the atlas square-ish.
    math::Size next_size(atlas_size);
    if (atlas_size.width() < max_size.width() &&
        (atlas_size.width() <= atlas_size.height() ||
        atlas_size.height() >= max_size.height())) {
      next_size.set_width(
          std::min(atlas_size.width() * 2, max_size.width()));
    } else if (atlas_size.height() < max_size.height()) {
      next_size.set_height(
          std::min(atlas_size.height() * 2, max_size.height()));
    } else {
      break;
    }
    if (GetMemorySize(next_size) > half_memory_limit) {
      break;
    }
    atlas_size = next_size;
  }

  // It is better to have fewer, large atlases than many small atlases to
  // minimize the cost of switching render targets. Consider changing the
  // max_size logic if there's plenty of memory to spare.
  const int kMaxAtlases = 4;
  int num_atlases = memory_limit_ / GetMemorySize(atlas_size);
  if (num_atlases < 2) {
    // Must have at least two atlases -- even if they are of a token size.
    // This simplifies code elsewhere.
    DCHECK(atlas_size.width() == 1 && atlas_size.height() == 1);
    num_atlases = 2;
  } else if (num_atlases > kMaxAtlases) {
    DCHECK(atlas_size == max_size);
    num_atlases = kMaxAtlases;
    DLOG(WARNING) << "More memory was allotted for offscreen render targets"
                  << " than will be used.";
  }
  offscreen_cache_.reset(CreateOffscreenAtlas(atlas_size));
  for (int i = 1; i < num_atlases; ++i) {
    offscreen_atlases_.push_back(CreateOffscreenAtlas(atlas_size));
  }

  DLOG(INFO) << "Created " << num_atlases << " offscreen atlases of size "
             << atlas_size.width() << " x " << atlas_size.height();
}

OffscreenTargetManager::OffscreenAtlas*
    OffscreenTargetManager::CreateOffscreenAtlas(const math::Size& size) {
  OffscreenAtlas* atlas = new OffscreenAtlas(size);

  // Create a new framebuffer.
  atlas->framebuffer = new backend::FramebufferRenderTargetEGL(
      graphics_context_, size);

  // Wrap the framebuffer as a skia surface.
  atlas->skia_surface.reset(create_fallback_surface_.Run(atlas->framebuffer));

  return atlas;
}

}  // namespace egl
}  // namespace rasterizer
}  // namespace renderer
}  // namespace cobalt