/* clear the surface just in case */
cairo_set_operator(marker->cairo, CAIRO_OPERATOR_SOURCE);
//cairo_set_source_rgba(marker->cairo, 1.0, 0.0, 0.0, 0.3); // debug
/* clear the surface just in case */
cairo_set_operator(marker->cairo, CAIRO_OPERATOR_SOURCE);
//cairo_set_source_rgba(marker->cairo, 1.0, 0.0, 0.0, 0.3); // debug