画布上的 Android Mask 位图生成黑色空间 [英] Android Mask bitmap on canvas gen a black space

问题描述

我有一个掩码位图，一半是红色，一半是透明的https://www.dropbox.com/s/931ixef6myzusi0/s_2.png

I have a mask bitmap with a half is red color and ones is transparent like this https://www.dropbox.com/s/931ixef6myzusi0/s_2.png

我想使用遮罩位图在画布上绘制仅在红色区域可见的内容，代码如下:

I want to use mask bitmap to draw content on canvas only visible in red area, code like this:

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);

}

结果如我所料(内容仅在红色区域可见，但透明区域变成黑色是问题！)

The result as my expecting (content only visible in red area, BUT THE TRANSPARENT AREA BECOME BLACK IS PROBLEM!)

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

this image result :https://www.dropbox.com/s/mqj48992wllfkiq/s_2%20copy.png Anyone help me???

推荐答案

这是一个帮助我实现屏蔽的解决方案:

Here is a solution which helped me to implement masking:

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());
}

遮罩应该是透明的白色图像.
它将像这样工作:
+ =

The mask should be a white image with transparency.
It will work like this:
+ =

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