圖片時，我想給它失真

Question

我發現SO和MSDN這些代碼，用於創建CAPTCHA圖像：

private Image DrawText(String text, Font font, Color textColor, Color backColor) 
    { 
     //first, create a dummy bitmap just to get a graphics object 
     Image img = new Bitmap(1, 1); 
     Graphics drawing = Graphics.FromImage(img); 

     //measure the string to see how big the image needs to be 
     SizeF textSize = drawing.MeasureString(text, font); 

     //free up the dummy image and old graphics object 
     img.Dispose(); 
     drawing.Dispose(); 

     //create a new image of the right size 
     Bitmap b = new Bitmap((int)textSize.Width, (int)textSize.Height); 
     int distortion = 2; 
     Bitmap copy = b; 
     for (int y = 0; y < textSize.Height; y++) 
     { 
      for (int x = 0; x < textSize.Width; x++) 
      { 
       int newX = (int)(x + (distortion * Math.Sin(Math.PI * y/64.0))); 
       int newY = (int)(y + (distortion * Math.Cos(Math.PI * x/64.0))); 
       if (newX < 0 || newX >= textSize.Width) newX = 0; 
       if (newY < 0 || newY >= textSize.Height) newY = 0; 
       b.SetPixel(x, y, copy.GetPixel(newX, newY)); 
      } 
     } 
     img = b; 
     drawing = Graphics.FromImage(img); 

     //paint the background 
     drawing.Clear(backColor); 

     //create a brush for the text 
     Brush textBrush = new SolidBrush(textColor); 

     drawing.DrawString(text, font, textBrush, 0, 0); 

     drawing.Save(); 

     textBrush.Dispose(); 
     drawing.Dispose(); 

     return img; 

    } 

我也使用此代碼輸出圖像輸出到瀏覽器：

Image image = DrawText("3", new Font("Thahoma", 20), Color.Black, Color.White); 
context.Response.ContentType = "image/png"; 
using (MemoryStream ms = new MemoryStream()) 
    { 
     image.Save(ms, System.Drawing.Imaging.ImageFormat.Png); 
     ms.WriteTo(context.Response.OutputStream); 
    } 

但是這段代碼不會輸出沒有任何錯誤的圖像;當我清除那些for時，它會顯示圖像。 我的web應用程序將運行在私人Intranet上，因此不建議使用reCAPTCHA！

Answer 1

原始DrawImage函數不能生成正確的位圖，因爲它有問題（例如，它對ArgumentOutOfRangeException失敗）。嘗試更正的版本：

Image DrawText(string text, Font font, Color textColor, Color backColor) { 
    Size textSize; 
    using(Image tmp = new Bitmap(1, 1)) { 
     using(Graphics g = Graphics.FromImage(tmp)) { 
      textSize = Size.Ceiling(g.MeasureString(text, font)); 
     } 
    } 
    Bitmap bitmap = new Bitmap(textSize.Width, textSize.Height); 
    using(Graphics g = Graphics.FromImage(bitmap)) { 
     g.Clear(backColor); 
     using(Brush textBrush = new SolidBrush(textColor)) { 
      g.DrawString(text, font, textBrush, 0, 0); 
     } 
    } 
    const double Distortion = 2.0; 
    const double F = Math.PI/64.0; 
    using(Bitmap copy = bitmap.Clone() as Bitmap) { 
     for(int y = 0; y < textSize.Height; y++) { 
      for(int x = 0; x < textSize.Width; x++) { 
       int newX = (int)(x + Distortion * Math.Sin(F * y)); 
       int newY = (int)(y + Distortion * Math.Cos(F * x)); 
       if(newX < 0 || newX >= textSize.Width) newX = 0; 
       if(newY < 0 || newY >= textSize.Height) newY = 0; 
       bitmap.SetPixel(x, y, copy.GetPixel(newX, newY)); 
      } 
     } 
    } 
    return bitmap; 
}