static Rect randomRect_enclosing_in(int w, int h, Rect inner, Rect outer) {
  if (inner.w > w || inner.h > h) null;
  if (outer.w < w || outer.h < h) null;
  IntRange x1range = intersectIntRanges(
    intRange_incl(inner.x2()-w, inner.x),
    intRange_incl(outer.x1(), outer.x2()-w));
  IntRange x2range = intersectIntRanges(
    intRange_incl(inner.x2(), inner.x+w),
    intRange_incl(outer.x1()+w, outer.x2()));
  if (x1range.isEmpty() || x2range.isEmpty()) null;
  IntRange y1range = intersectIntRanges(
    intRange_incl(inner.y2()-h, inner.y),
    intRange_incl(outer.y1(), outer.y2()-h));
  IntRange y2range = intersectIntRanges(
    intRange_incl(inner.y2(), inner.y+h),
    intRange_incl(outer.y1()+h, outer.y2()));
  if (y1range.isEmpty() || y2range.isEmpty()) null;
  ret rectFromPoints(random(x1range), random(y1range),
    random(x2range), random(x2range));
}