画布上的Android Mask位图生成黑色空间

Question

我有一个蒙版位图，一半是红色，一个是透明的，像这样 https://www.dropbox.com/s/931ixef6myzusi0/s_2.png

我想用遮罩位图在画布上绘制内容，只在红色区域可见，代码如下：

Paint paint = new Paint();


public void draw(Canvas canvas) {
// draw content here
  ...

//and mask bitmap here
  paint.setXfermode(new PorterDuffXfermode(android.graphics.PorterDuff.Mode.DST_IN));
  canvas.drawBitmap(maskBitmap, 0, 0, paint);

}

结果如我所愿（内容仅在红色区域可见，但透明区域变为黑色是问题！）

此图像结果：https://www.dropbox.com/s/mqj48992wllfkiq/s_2%20copy.png 有人帮我吗？？？

Answer 1

这是一个帮助我实现屏蔽的解决方案：

public void draw(Canvas canvas) {
        Bitmap original = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.original_image);
        Bitmap mask = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.mask_image);

        //You can change original image here and draw anything you want to be masked on it.

        Bitmap result = Bitmap.createBitmap(mask.getWidth(), mask.getHeight(), Config.ARGB_8888);
        Canvas tempCanvas = new Canvas(result);
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
        tempCanvas.drawBitmap(original, 0, 0, null);
        tempCanvas.drawBitmap(mask, 0, 0, paint);
        paint.setXfermode(null);

        //Draw result after performing masking
        canvas.drawBitmap(result, 0, 0, new Paint());
}

蒙版应该是具有透明度的白色图像。
它将像这样工作：
+ =

Answer 2

我在自定义视图中遇到了同样的问题，我没有从资源中解码位图，而是通过canvas.draw*() 方法从头开始创建了原始位图和掩码位图（因为原始位图和蒙版都是基本形状）。我得到的是blank opaque space，而不是transparent。我通过在我的视图中设置一个硬件层来修复它。

View.setLayerType(LAYER_TYPE_HARDWARE, paint);

更多关于为什么要这样做的信息：https://stackoverflow.com/a/33483016/4747587

Answer 3

Bitmap finalMasking = stackMaskingProcess(imageBitmap, bitmapMasking);


private Bitmap stackMaskingProcess(Bitmap _originalBitmap, Bitmap _maskingBitmap) {
        try {
            if (_originalBitmap != null)
            {
                int intWidth = _originalBitmap.getWidth();
                int intHeight = _originalBitmap.getHeight();
                resultMaskBitmap = Bitmap.createBitmap(intWidth, intHeight, Bitmap.Config.ARGB_8888);
                getMaskBitmap = Bitmap.createScaledBitmap(_maskingBitmap, intWidth, intHeight, true);
                Canvas mCanvas = new Canvas(resultMaskBitmap);
                Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
                paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
                mCanvas.drawBitmap(_originalBitmap, 0, 0, null);
                mCanvas.drawBitmap(getMaskBitmap, 0, 0, paint);
                paint.setXfermode(null);
                paint.setStyle(Paint.Style.STROKE);
            }
        } catch (OutOfMemoryError o) {
            o.printStackTrace();
        }
        return resultMaskBitmap;
    }

Answer 4

我喜欢Er. Praful Parmar's 答案中的方法，但对我来说，它并没有达到预期的效果。我遇到了问题，因为一些扩展是在无意中进行的。
我的位图的密度与我的设备不同，这搞砸了。

另外我想减少对象的创建，所以我将Paint对象移动到一个常量中以便重复使用。

这是我的 utils 方法：

  public static final//
  Bitmap createWithMask(final Bitmap img, final Bitmap mask) {
    final Bitmap result = Bitmap.createBitmap(img.getWidth(), img.getHeight(),
        Bitmap.Config.ARGB_8888);
    result.setDensity(originalBitmap.getDensity()); // to avoid scaling if density of 'img' is different form the default on your device
    final Canvas canvas = new Canvas(result);
    canvas.drawBitmap(img, 0, 0, null);
    canvas.drawBitmap(mask, 0, 0, PAINT_FOR_MASK);
    return result;
  }//end-method

  private static final Paint PAINT_FOR_MASK = createPaintForMask();

  private static final//
  Paint createPaintForMask() {
    final Paint paint = new Paint();
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
    return paint;
  }//end-method

Answer 5

与@Sergey Pekar 给出的答案相同，但我已在 Kotlin 中进行了更新。

fun ImageView.getMaskBitmap(imageUrl: String? = null, mContent: Int, mMaskedImage : Int) {
    runOnBackground {
        // if you have https image url then use below line
        //val original: Bitmap = BitmapFactory.decodeStream(URL(imageUrl).openConnection().getInputStream())

        // if you have png or jpg image then use below line
        val original: Bitmap = BitmapFactory.decodeResource(resources, mContent)

        val mask = BitmapFactory.decodeResource(resources, mMaskedImage) // mMaskedImage Your masking image
        val result: Bitmap = Bitmap.createBitmap(mask.width, mask.height, Bitmap.Config.ARGB_8888, true)
        val tempCanvas = Canvas(result)
        val paint = Paint(Paint.ANTI_ALIAS_FLAG)
        paint.xfermode = PorterDuffXfermode(PorterDuff.Mode.DST_IN)
        tempCanvas.apply {
            drawBitmap(original, 0f, 0f, null)
            drawBitmap(mask, 0f, 0f, paint)
        }
        paint.xfermode = null

        //Draw result after performing masking
        runOnBackground(onMainThread = {
            this.apply {
                setImageBitmap(result)
                scaleType = ImageView.ScaleType.FIT_CENTER
            }
        })
    }
}

Github Demo