vardef hsv_color(expr h, s, v) =
  save chroma, hh, x, m;
  chroma = v * s;
  hh = h / 60;
  x  = chroma * (1 - abs(hh mod 2 - 1));
  m  = v - chroma;
  if     hh < 1: (chroma,x,0)+(m,m,m)
  elseif hh < 2: (x,chroma,0)+(m,m,m)
  elseif hh < 3: (0,chroma,x)+(m,m,m)
  elseif hh < 4: (0,x,chroma)+(m,m,m)
  elseif hh < 5: (x,0,chroma)+(m,m,m)
  else:          (chroma,0,x)+(m,m,m)
  fi
enddef;