GLX_NV_copy_buffer
http://www.opengl.org/registry/specs/NV/glx_copy_buffer.txt
GLX_NV_copy_buffer

	void glXCopyBufferSubDataNV (Display* dpy, GLXContext readCtx, GLXContext writeCtx, GLenum readTarget, GLenum writeTarget, GLintptr readOffset, GLintptr writeOffset, GLsizeiptr size)
	void glXNamedCopyBufferSubDataNV (Display* dpy, GLXContext readCtx, GLXContext writeCtx, GLuint readBuffer, GLuint writeBuffer, GLintptr readOffset, GLintptr writeOffset, GLsizeiptr size)