// The hash for an image without alpha channel is guaranteed to be
// identical for a completely opaque image with alpha.
srecord noeq HashBufferedImage(BufferedImage img) {
  long hash;
  
  long get() {
    if (img == null) ret hash;
    
    var gp = grabbableIntPixels_fastOrSlow(img);
    bool hasAlpha = hasAlpha(img);
    
    var ping = pingSource();
    int[] pixelsIn = gp.data;
    int w = gp.w, h = gp.h;
    int scanlineExtra = gp.scanlineStride-w;
    int iIn = gp.offset;

    addToHash(w);
    addToHash(h);
    
    for y to h: {
      for x to w: {
        int packed = pixelsIn[iIn++];
        if (!hasAlpha) packed |= 0xFF000000;
        addToHash(packed);
      }

      iIn += scanlineExtra;
      ping?!;
    }
    
    ret hash;
  }
  
  void addToHash(long x) {
    hash = boostHashCombine64(hash, x);
    printVars ifdef HashBufferedImage_debug(x := longToHex(x), +hash);
  }
}