code: func (captcha *CaptchaImage) DrawText(text string) *CaptchaImage {
  	if captcha.Error != nil {
  		return captcha
  	}
  	c := freetype.NewContext()
  	c.SetDPI(*dpi)
  
  	c.SetClip(captcha.nrgba.Bounds())
  	c.SetDst(captcha.nrgba)
  	c.SetHinting(font.HintingFull)
  
  	fontWidth := captcha.width / len(text)
  
  	for i, s := range text {
  
  		fontSize := float64(captcha.height) / (1 + float64(r.Intn(7))/float64(9))
  
  		c.SetSrc(image.NewUniform(randDeepColor()))
  		c.SetFontSize(fontSize)
  		f, err := RandFontFamily()
  
  		if err != nil {
  			captcha.Error = err
  			return captcha
  		}
  		c.SetFont(f)
  
  		x := int(fontWidth)*i + int(fontWidth)/int(fontSize)
  
  		y := 5 + r.Intn(captcha.height/2) + int(fontSize/2)
  
  		pt := freetype.Pt(x, y)
  
  		_, err = c.DrawString(string(s), pt)
  		if err != nil {
  			captcha.Error = err
  			return captcha
  		}
  		//pt.Y += c.PointToFixed(*size * *spacing)
  		//pt.X += c.PointToFixed(*size);
  	}
  	return captcha
  
  }
docs: //写字.