code: func makeScale(x1, x2 float64, y1, y2 int) scale.QQ {
  	return scale.QQ{
  		Src:  &scale.Linear{Min: x1, Max: x2, Clamp: true},
  		Dest: &scale.Linear{Min: float64(y1), Max: float64(y2) - 1e-10},
  	}
  }
docs: // makeScale creates a linear scale from [x1, x2) to [y1, y2).