Android 遮罩效果

最终效果图：

背景图

由于图片是白色的，所以跟网页背景混在一起了

前景图

代码

public class MaskImageView extends ImageView {

    private Xfermode mXfermode = new PorterDuffXfermode(PorterDuff.Mode.SRC_IN);

    public MaskImageView(Context context) {
        this(context, null);
    }

    public MaskImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MaskImageView(Context context, AttributeSet attrs, int defStyle, Paint paint) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (!(getDrawable() instanceof BitmapDrawable)) {
            super.onDraw(canvas);
            return;
        }

        int saveFlags = Canvas.MATRIX_SAVE_FLAG
            | Canvas.CLIP_SAVE_FLAG
            | Canvas.HAS_ALPHA_LAYER_SAVE_FLAG
            | Canvas.FULL_COLOR_LAYER_SAVE_FLAG
            | Canvas.CLIP_TO_LAYER_SAVE_FLAG;
        canvas.saveLayer(0, 0, getWidth(), getHeight(), null, saveFlags);

        getBackground().draw(canvas);
        BitmapDrawable image = (BitmapDrawable) getDrawable();
        image.getPaint().setXfermode(mXfermode);
        image.draw(canvas);

        canvas.restore();
    }
}