glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
+DCPOMATIC_DISABLE_WARNINGS
gluOrtho2D (0, canvas_size.GetWidth(), canvas_size.GetHeight(), 0);
+DCPOMATIC_ENABLE_WARNINGS
check_gl_error ("gluOrtho2d");
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();