void snap(const int p, const prevPlanes &pp, ColorVal &min, ColorVal &max, ColorVal &v) const {
if (p==0 || p==3) { min=bounds[p].first; max=bounds[p].second; } // optimization for special case
else ranges->snap(p,pp,min,max,v);
if (min < bounds[p].first) min=bounds[p].first;
if (max > bounds[p].second) max=bounds[p].second;
if (min>max) {
// should happen only if alpha=0 interpolation produces YI combination for which Q range from ColorRangesYIQ is outside bounds
min=bounds[p].first;
max=bounds[p].second;
}
if(v>max) v=max;
if(v<min) v=min;
}
bool exists(const int p, const prevPlanes &pp) const {
if (p>0 && (pp[0] < min0 || pp[0] > ranges->max(0))) return false;
if (p>1 && (pp[1] < min1 || pp[1] > ranges->max(1))) return false;
ColorVal rmin, rmax;
ColorVal v=pp[p];
ranges->snap(p,pp,rmin,rmax,v);
if (v != pp[p]) return false; // bucket empty because of original range constraints
const ColorBucket b = findBucket(p,pp);
//if (b.min > b.max) return false;
if (b.snapColor_slow(pp[p]) != pp[p]) return false;
return true;
}