android drawBitmap with PorterDuff.Mode.DST_IN ,应该透明的区域变成黑色

Question

我正在尝试绘制带有特定形状遮罩的图像。我正在使用 Facebook 的图书馆 Fresco，这里是代码：

    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);

此代码在 5.0.2 上运行良好... 我无法在此处 post 图片，请参阅 http://i.stack.imgur.com/9DBbj.jpg

但在 4.4.4 和 4.1.2 上失败。我无法在此处 post 图片，请参阅 http://i.stack.imgur.com/8wbLp.jpg

我还在 5.0.2 上打印了 "temp" 左上角像素的颜色并裁剪了 "bitmap"，即 #00000000 和 #00000000，在 4.4.4 和 4.1.2 上它们是#00000000 和#FF000000

Answer 1

我很高兴在 Fresco 的 github 问题页面上找到答案 here

正如它所说，我只需要调用

    bitmap.setHasAlpha(true);

在

    public void process(Bitmap bitmap)

android drawBitmap with PorterDuff.Mode.DST_IN ,应该透明的区域变成黑色

android drawBitmap with PorterDuff.Mode.DST_IN ,the area which should be transparent turn out to be black

android

canvas

bitmap

draw