GPUProcessor uses O3D command buffer service to render to a window....

o3d/command_buffer/service/cross/cmd_buffer_engine.h

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 28 matching lines @@
 #include <vector>
 #include "base/scoped_ptr.h"
 #include "command_buffer/common/cross/buffer_sync_api.h"
 #include "command_buffer/service/cross/cmd_parser.h"
 
 namespace o3d {
 namespace command_buffer {
 
 class BufferRPCImpl;
 
-class CommandBufferEngine : public BufferSyncInterface {
+class CommandBufferUpcallInterface {
+ public:
+  CommandBufferUpcallInterface() {
+  }
+
+  virtual ~CommandBufferUpcallInterface() {
+  }
+
+  // Gets the base address of a registered shared memory buffer.
+  // Parameters:
+  //   shm_id: the identifier for the shared memory buffer.
+  virtual void *GetSharedMemoryAddress(unsigned int shm_id) = 0;
+
+  // Gets the size of a registered shared memory buffer.
+  // Parameters:
+  //   shm_id: the identifier for the shared memory buffer.
+  virtual size_t GetSharedMemorySize(unsigned int shm_id) = 0;
+
+  // Sets the token value.
+  virtual void set_token(unsigned int token) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CommandBufferUpcallInterface);
+};
+
+class CommandBufferEngine : public BufferSyncInterface,
+                            public CommandBufferUpcallInterface {
  public:
   explicit CommandBufferEngine(AsyncAPIInterface *handler);
   virtual ~CommandBufferEngine();
 
   // Initializes the connection with the client.
   virtual void InitConnection();
 
   // Closes the connection with the client.
   virtual void CloseConnection();
 
@@ skipping 145 matching lines @@
     void *address;
     size_t size;
   };
   std::vector<MemoryMapping> shared_memory_buffers_;
 };
 
 }  // namespace command_buffer
 }  // namespace o3d
 
 #endif  // O3D_COMMAND_BUFFER_SERVICE_CROSS_CMD_BUFFER_ENGINE_H_