code: func DrawLine(dst *ebiten.Image, x1, y1, x2, y2 float64, clr color.Color) {
  	ew, eh := emptyImage.Size()
  	length := math.Hypot(x2-x1, y2-y1)
  
  	op := &ebiten.DrawImageOptions{}
  	op.GeoM.Scale(length/float64(ew), 1/float64(eh))
  	op.GeoM.Rotate(math.Atan2(y2-y1, x2-x1))
  	op.GeoM.Translate(x1, y1)
  	op.ColorM.Scale(colorScale(clr))
  	// Filter must be 'nearest' filter (default).
  	// Linear filtering would make edges blurred.
  	_ = dst.DrawImage(emptyImage, op)
  }
docs: // DrawLine draws a line segment on the given destination dst.
  //
  // DrawLine is intended to be used mainly for debugging or prototyping purpose.