GL_ARB_copy_buffer
http://www.opengl.org/registry/specs/gl/ARB/copy_buffer.txt
GL_ARB_copy_buffer
	GL_COPY_READ_BUFFER 0x8F36
	GL_COPY_WRITE_BUFFER 0x8F37
	void glCopyBufferSubData (GLenum readtarget, GLenum writetarget, GLintptr readoffset, GLintptr writeoffset, GLsizeiptr size)