BlobDetection library question

lki92

Can someone please explain to me what is this code doing? This is from one of the built in libraries called blobDetection. Thanks!

void fastblur(PImage img,int radius)
{
 if (radius<1)
    return;

  int w = img.width;
  int h = img.height;
  int wm = w-1;
  int hm = h-1;
  int area = w*h;
  int div = radius+radius+1;
  int r[] = new int[area];
  int g[] = new int[area];
  int b[] = new int[area];
  int rsum,gsum,bsum,x,y,i,p,p1,p2,yp,yi,yw;
  int vmin[] = new int[max(w,h)];
  int vmax[] = new int[max(w,h)];
  int[] pix = img.pixels;
  int dv[] = new int[256*div];
  for (i=0; i<256*div; i++)
    dv[i]=(i/div);

  yw = yi =0;

  for (y=0; y<h; y++)
  {
    rsum = gsum = bsum = 0;
    for(i=-radius; i<=radius; i++)
    {
      p = pix[yi+min(wm,max(i,0))];
      rsum += (p & 0xff0000)>>16;
      gsum += (p & 0x00ff00)>>8;
      bsum += p & 0x0000ff;
    }
    for (x=0; x<w; x++)
    {

      r[yi]=dv[rsum];
      g[yi]=dv[gsum];
      b[yi]=dv[bsum];

      if(y==0)
      {
        vmin[x] = min(x+radius+1,wm);
        vmax[x] = max(x-radius,0);
      }
      p1 = pix[yw+vmin[x]];
      p2 = pix[yw+vmax[x]];

      rsum += ((p1 & 0xff0000)-(p2 & 0xff0000))>>16;
      gsum += ((p1 & 0x00ff00)-(p2 & 0x00ff00))>>8;
      bsum += (p1 & 0x0000ff)-(p2 & 0x0000ff);
      yi++;
    }
    yw+=w;
  }

  for (x=0; x<w; x++)
  {
    rsum = gsum = bsum = 0;
    yp =- radius*w;
    for(i = -radius; i<=radius; i++){
      yi = max(0,yp)+x;
      rsum += r[yi];
      gsum += g[yi];
      bsum += b[yi];
      yp += w;
    }
    yi = x;
    for (y=0; y<h; y++)
    {
      pix[yi]=0xff000000 | (dv[rsum]<<16) | (dv[gsum]<<8) | dv[bsum];
      if(x==0)
      {
        vmin[y] = min(y+radius+1,hm)*w;
        vmax[y] = max(y-radius,0)*w;
      }
      p1 = x+vmin[y];
      p2 = x+vmax[y];

      rsum += r[p1]-r[p2];
      gsum += g[p1]-g[p2];
      bsum += b[p1]-b[p2];

      yi += w;
    }
  }

}