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

// Copyright 2017 The Cobalt Authors. 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.

#ifndef COBALT_RENDERER_RASTERIZER_EGL_OFFSCREEN_TARGET_MANAGER_H_
#define COBALT_RENDERER_RASTERIZER_EGL_OFFSCREEN_TARGET_MANAGER_H_

#include <memory>

#include "base/callback.h"
#include "cobalt/math/rect_f.h"
#include "cobalt/math/size.h"
#include "cobalt/render_tree/node.h"
#include "cobalt/renderer/backend/egl/framebuffer_render_target.h"
#include "cobalt/renderer/backend/egl/graphics_context.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/core/SkSurface.h"

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

// Manage allocating and caching offscreen render targets for render_tree::Node
// rendering. This uses atlases instead of individual render targets to
// minimize the cost of switching render targets.
class OffscreenTargetManager {
 public:
  typedef base::Callback<sk_sp<SkSurface>(const backend::RenderTarget*)>
      CreateFallbackSurfaceFunction;

  struct TargetInfo {
    TargetInfo() : framebuffer(NULL), skia_canvas(NULL) {}
    backend::FramebufferRenderTargetEGL* framebuffer;
    SkCanvas* skia_canvas;
    math::RectF region;
  };

  // Offscreen targets are cached with additional ErrorData. When searching for
  // a match, the caller specifies an error function which is used to verify
  // that a particular cache entry is suitable for use. A cache entry is
  // suitable if CacheErrorFunction(ErrorData) < |cache_error_threshold_|. If
  // multiple entries meet this criteria, then the entry with the lowest error
  // is chosen.
  typedef math::RectF ErrorData;
  typedef base::Callback<float(const ErrorData&)> CacheErrorFunction;
  typedef float ErrorData1D;
  typedef base::Callback<float(const ErrorData1D&)> CacheErrorFunction1D;

  OffscreenTargetManager(
      backend::GraphicsContextEGL* graphics_context,
      const CreateFallbackSurfaceFunction& create_fallback_surface,
      size_t memory_limit);
  ~OffscreenTargetManager();

  // Update must be called once per frame, before any allocation requests are
  // made for that frame.
  void Update(const math::Size& frame_size);

  // Flush all render targets that have been used thus far.
  void Flush();

  // Specify the acceptable limit for the return value of the cache error
  // function. A cached target can be a match only if the error value is less
  // than the specified threshold. The default threshold is 1.
  void SetCacheErrorThreshold(float threshold);

  // Return whether a cached version of the requested render target is
  // available. If a cache does exist, then the output parameters are set,
  // otherwise, they are untouched.
  // The returned values are only valid until the next call to Update().
  bool GetCachedTarget(const render_tree::Node* node,
                       const CacheErrorFunction& error_function,
                       TargetInfo* out_target_info);
  bool GetCachedTarget(const render_tree::Node* node,
                       const CacheErrorFunction1D& error_function,
                       TargetInfo* out_target_info);

  // Allocate a cached offscreen target of the specified size.
  // The returned values are only valid until the next call to Update().
  void AllocateCachedTarget(const render_tree::Node* node,
                            const math::SizeF& size,
                            const ErrorData& error_data,
                            TargetInfo* out_target_info);
  void AllocateCachedTarget(const render_tree::Node* node, float size,
                            const ErrorData1D& error_data,
                            TargetInfo* out_target_info);

  // Allocate an uncached render target. The contents of the target cannot be
  // reused in subsequent frames.  If there was an error allocating the
  // render target, out_target_info->framebuffer will be set to nullptr.
  void AllocateUncachedTarget(const math::SizeF& size,
                              TargetInfo* out_target_info);

 private:
  // Use an atlas for offscreen targets.
  struct OffscreenAtlas;

  void InitializeTargets(const math::Size& frame_size);
  std::unique_ptr<OffscreenAtlas> CreateOffscreenAtlas(const math::Size& size,
                                                       bool create_canvas);
  void SelectAtlasCache(std::vector<std::unique_ptr<OffscreenAtlas>>* atlases,
                        std::unique_ptr<OffscreenAtlas>* cache);

  backend::GraphicsContextEGL* graphics_context_;
  CreateFallbackSurfaceFunction create_fallback_surface_;

  std::vector<std::unique_ptr<OffscreenAtlas>> offscreen_atlases_;
  std::unique_ptr<OffscreenAtlas> offscreen_cache_;

  std::vector<std::unique_ptr<OffscreenAtlas>> offscreen_atlases_1d_;
  std::unique_ptr<OffscreenAtlas> offscreen_cache_1d_;

  std::vector<std::unique_ptr<OffscreenAtlas>> uncached_targets_;

  // Align offscreen targets to a particular size to more efficiently use the
  // offscreen target atlas. Use a power of 2 for the alignment so that a bit
  // mask can be used for the alignment calculation.
  math::Size offscreen_target_size_mask_;

  // Maximum number of bytes that can be used for offscreen atlases.
  size_t memory_limit_;

  // A cached target can be a match only if the cache error function returns
  // a value less than the cache error threshold.
  float cache_error_threshold_;
};

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

#endif  // COBALT_RENDERER_RASTERIZER_EGL_OFFSCREEN_TARGET_MANAGER_H_