Someone

void 
surface_clear (Surface *s, int x, int y, int width, int height)
{
	cairo_save (s->cairo);
	cairo_set_source_rgba (s->cairo, 1.0, 1.0, 1.0, 1.0);
	cairo_set_operator (s->cairo, CAIRO_OPERATOR_SOURCE);
	cairo_paint (s->cairo);
	cairo_restore (s->cairo);
}