/// fd_rectangle_clear(instance id);
function fd_rectangle_clear(domain) {
	// Clears the fluid dynamics rectangle, removing all its content.
	// instance id: The instance id of the fluid dynamics rectangle.

	with (domain) {
	    surface_free(sf_pressure);
	    surface_free(sf_velocity);
	    surface_free(sf_material_0); surface_free(sf_material_1);
	    surface_free(sf_world);
	}
}