rem: filterf = Mitchell_support; fwidth = Mitchell_filter;
add: filterf = Mitchell_filter; fwidth = Mitchell_support;
context: _wraster_change_filter(int type){    switch (type) {     case RBoxFilter:	filterf = box_filter;	fwidth = box_support;	break;     case RTriangleFilter:	filterf = triangle_filter;	fwidth = triangle_support;	break;     case RBellFilter:	filterf = bell_filter;	fwidth = bell_support;	break;     case RBSplineFilter:	filterf = B_spline_filter;	fwidth = B_spline_support;	break;     case RLanczos3Filter:	filterf = Lanczos3_filter;	fwidth = Lanczos3_support;	break;     default:     case RMitchellFilter:	filterf = Mitchell_support;	fwidth = Mitchell_filter;	break;    }}