code: func MakePictureData(rect Rect) *PictureData {
  	w := int(math.Ceil(rect.Max.X)) - int(math.Floor(rect.Min.X))
  	h := int(math.Ceil(rect.Max.Y)) - int(math.Floor(rect.Min.Y))
  	pd := &PictureData{
  		Stride: w,
  		Rect:   rect,
  	}
  	pd.Pix = make([]color.RGBA, w*h)
  	return pd
  }
docs: // MakePictureData creates a zero-initialized PictureData covering the given rectangle.