gpu/command_buffer/service/transform_feedback_manager.h

// Copyright (c) 2016 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 GPU_COMMAND_BUFFER_SERVICE_TRANSFORM_FEEDBACK_MANAGER_H_
#define GPU_COMMAND_BUFFER_SERVICE_TRANSFORM_FEEDBACK_MANAGER_H_

#include <unordered_map>
#include <vector>

#include "base/memory/ref_counted.h"
#include "gpu/command_buffer/service/gl_utils.h"
#include "gpu/command_buffer/service/indexed_buffer_binding_host.h"
#include "gpu/gpu_gles2_export.h"

namespace gpu {
namespace gles2 {

class Buffer;
class TransformFeedbackManager;

// Info about TransformFeedbacks currently in the system.
class GPU_GLES2_EXPORT TransformFeedback : public IndexedBufferBindingHost {
 public:
  TransformFeedback(TransformFeedbackManager* manager,
                    GLuint client_id,
                    GLuint service_id);

  // All the following functions do state update and call the underlying GL
  // function.  All validations have been done already and the GL function is
  // guaranteed to succeed.
  void DoBindTransformFeedback(GLenum target,
                               TransformFeedback* last_bound_transform_feedback,
                               Buffer* bound_transform_feedback_buffer);
  void DoBeginTransformFeedback(GLenum primitive_mode);
  void DoEndTransformFeedback();
  void DoPauseTransformFeedback();
  void DoResumeTransformFeedback();

  GLuint client_id() const {
    return client_id_;
  }

  GLuint service_id() const {
    return service_id_;
  }

  bool has_been_bound() const {
    return has_been_bound_;
  }

  bool active() const {
    return active_;
  }

  bool paused() const {
    return paused_;
  }

  GLenum primitive_mode() const {
    return primitive_mode_;
  }

  // Calculates the number of vertices that this draw call will write to the
  // transform feedback buffer, plus the number of vertices that were previously
  // written since the last call to BeginTransformFeedback (because vertices are
  // written starting just after the last vertex written by the previous draw),
  // plus |pending_vertices_drawn|. The pending vertices are used to iteratively
  // validate and accumulate the number of vertices drawn for multiple draws.
  // This is used to calculate whether there is enough space in the transform
  // feedback buffers. Returns false on integer overflow.
  bool GetVerticesNeededForDraw(GLenum mode,
                                GLsizei count,
                                GLsizei primcount,
                                GLsizei pending_vertices_drawn,
                                GLsizei* vertices_out) const;
  // This must be called every time a transform feedback draw happens to keep
  // track of how many vertices have been written to the transform feedback
  // buffers.
  void OnVerticesDrawn(GLsizei vertices_drawn);

 private:
  ~TransformFeedback() override;

  // The manager that owns this Buffer.
  TransformFeedbackManager* manager_;

  GLuint client_id_;
  GLuint service_id_;

  bool has_been_bound_;

  bool active_;
  bool paused_;

  GLenum primitive_mode_;
  GLsizei vertices_drawn_;
};

// This class keeps tracks of the transform feedbacks and their states.
class GPU_GLES2_EXPORT TransformFeedbackManager {
 public:
  // In theory |needs_emulation| needs to be true on Desktop GL 4.1 or lower.
  // However, we set it to true everywhere, not to trust drivers to handle
  // out-of-bounds buffer accesses.
  TransformFeedbackManager(GLuint max_transform_feedback_separate_attribs,
                           bool needs_emulation);
  ~TransformFeedbackManager();

  void MarkContextLost() {
    lost_context_ = true;
  }

  // Must call before destruction.
  void Destroy();

  // Creates a TransformFeedback from the given client/service IDs and
  // insert it into the list.
  TransformFeedback* CreateTransformFeedback(
      GLuint client_id, GLuint service_id);

  TransformFeedback* GetTransformFeedback(GLuint client_id);

  // Removes a TransformFeedback info for the given client ID.
  void RemoveTransformFeedback(GLuint client_id);

  GLuint max_transform_feedback_separate_attribs() const {
    return max_transform_feedback_separate_attribs_;
  }

  bool needs_emulation() const {
    return needs_emulation_;
  }

  bool lost_context() const {
    return lost_context_;
  }

 private:
  // Info for each transform feedback in the system.
  std::unordered_map<GLuint, scoped_refptr<TransformFeedback>>
      transform_feedbacks_;

  GLuint max_transform_feedback_separate_attribs_;

  bool needs_emulation_;
  bool lost_context_;

  DISALLOW_COPY_AND_ASSIGN(TransformFeedbackManager);
};

}  // namespace gles2
}  // namespace gpu

#endif  // GPU_COMMAND_BUFFER_SERVICE_TRANSFORM_FEEDBACK_MANAGER_H_