rem: strcat(RErrorString, ":could not convert RImage mask to XImage");
context: RConvertImageMask(RContext *context, RImage *image, Pixmap *pixmap, 		  Pixmap *mask, int threshold){    GC gc;    XGCValues gcv;    RXImage *ximg=NULL;    assert(context!=NULL);    assert(image!=NULL);    assert(pixmap!=NULL);    assert(mask!=NULL);    if (!RConvertImage(context, image, pixmap))	return False;        if (image->data[3]==NULL) {	*mask = None;	return True;    }    ximg = image2Bitmap(context, image, threshold);        if (!ximg) {	strcat(RErrorString, ":could not convert RImage mask to XImage");#ifdef C_ALLOCA	alloca(0);#endif	return False;    }    *mask = XCreatePixmap(context->dpy, context->drawable, image->width,			  image->height, 1);    gcv.foreground = context->black;    gcv.background = context->white;    gcv.graphics_exposures = False;    gc = XCreateGC(context->dpy, *mask, GCForeground|GCBackground		   |GCGraphicsExposures, &gcv);    RPutXImage(context, *mask, gc, ximg, 0, 0, 0, 0,	       image->width, image->height);    RDestroyXImage(context, ximg);#ifdef C_ALLOCA    alloca(0);#endif    return True;}