track :
  -v -
  h=0 s=0 v=0
  -do
    -camera
    --blur[-1] 1 -n[-1] 0,255 -rgb2hsv[-1]
    -shared[-1] 0,0 -n[-1] 0,100 -rm[-1]
    -shared[-1] 1,1 -n[-1] 0,16 -rm[-1]
    -shared[-1] 2,2 -n[-1] 0,0 -rm[-1]
    -if {@{!,b}\&1}  # Select object color.
      x=@{!,x} y=@{!,y}
      h=@{-1,($x,$y,0,0)}
      s=@{-1,($x,$y,0,1)}
      v=@{-1,($x,$y,0,2)}
    -endif
    -select_color[-1] 3,$h,$s,$v -erode[-1] 8 -dilate[-1] 8
    -w2[-1]
    -i[-2] ({w-1},0;{w-1},0^0,{w-1};0,{w-1}^{h-1},{h-1};0,0^0,0;{h-1},{h-1}) -r[-2] [-1],[-1],1,4,3 -*[-2,-1]
    --shared[-1] 0,0 xmin={w-1-iM} -rm[-1]
    --shared[-1] 1,1 xmax={iM} -rm[-1]
    --shared[-1] 2,2 ymin={h-1-iM} -rm[-1]
    --shared[-1] 3,3 ymax={iM} -rm[-1]
    -rm[-1]
    -if {$xmin!=w-1" || "$xmax!=0" || "$ymin!=h-1" || "$ymax!=0}
    -polygon[-1] 4,$xmin,$ymin,$xmax,$ymin,$xmax,$ymax,$xmin,$ymax,1,0xFFFFFFFF,255
    -ellipse {($xmin+$xmax)/2},{($ymin+$ymax)/2},8,8,0,1,255,0,255
    -else
    1,1 -text[-1] "Object not found",2,2,24,1,255,255,255 -image[-2] [-1],10,10,0,0,0.3 -rm[-1]
    -endif
    -w[-1] -1,-1,0,0,"Tracking demo (h="$h",s="$s",v="$v")"
    -rm[-1]
    -wait 20
  -while @!