android drawBitmap和PorterDuff.Mode.DST_IN，應該是透明的區域是黑色的

Question

我想繪製一個具有特定形狀的面具的圖像。 我使用Facebook的庫壁畫，這裏是代碼：

ImageRequest request = builder.setPostprocessor(new BasePostprocessor() { 
     @Override 
     public String getName() { 
      return "ChatViewImageProcessor"; 
     } 

     @Override 
     public void process(Bitmap bitmap) { 
      int bitmap_width = bitmap.getWidth(); 
      int bitmap_height = bitmap.getHeight(); 
      ViewGroup.LayoutParams params = iv.getLayoutParams(); 
      if (width == -1 && height == -1) {//not relavant with question 
       horizontal[0] = bitmap_width >= bitmap_height; 
       params.width = horizontal[0] ? max_image_size : (int) (max_image_size * 1.0 * bitmap_width/bitmap_height); 
       params.height = (horizontal[0] ? (int) (max_image_size * 1.0 * bitmap_height/bitmap_width) : max_image_size); 

      } 

      Bitmap temp = Bitmap.createBitmap(params.width, params.height, Bitmap.Config.ARGB_8888); 
      Canvas canvas = new Canvas(temp); 
      if (bg != null) { 
       bg.setBounds(0, 0, params.width, params.height); 
       bg.draw(canvas); 
      } 
      Logger.out("temp[0,0]:" + Util.getColorNote(temp.getPixel(0, 0), true)); 
      canvas = new Canvas(bitmap); 

      Rect src = new Rect(0, 0, temp.getWidth(), temp.getHeight()); 
      Rect dst = new Rect(0, 0, bitmap_width, bitmap_height); 
      canvas.drawBitmap(temp, src, dst, paint);//<----------problem here 

      temp.recycle(); 
      Logger.out("result[0,0]:" + Util.getColorNote(bitmap.getPixel(0, 0), true)); 
     } 
    }).build(); 

    PipelineDraweeController controller = (PipelineDraweeController) 
      Fresco.newDraweeControllerBuilder() 
        .setImageRequest(request) 
        .setOldController(iv.getController()) 
        .build(); 
    iv.setController(controller); 

此代碼適用於5.0.2就好了... ... 我不能發佈的形象在這裏，看到http://i.stack.imgur.com/9DBbj.jpg

但失敗在4.4.4和4.1.2上。 我不能在這裏發佈圖片，看http://i.stack.imgur.com/8wbLp.jpg

我還打印了左上角像素的顏色「temp」，並在4.4.2上修剪了5.0.2上的「位圖」，即＃00000000和＃00000000。 4 4.1.2他們是＃00000000和＃FF000000

Answer 1

我很高興地發現壁畫的GitHub的問題頁面here

的答案，因爲它說，我只需要調用

bitmap.setHasAlpha(true); 

in

public void process(Bitmap bitmap)