安卓：自定义view实现刮刮乐的效果：

这里用到了

不会的可以去看一下自定义view的讲解:

https://note.youdao.com/ynoteshare/index.html?id=a99fc369bc9d4c448cb44af0c542a381&type=note

public class G extends View {
    private Paint paint_one;
    private Path mpath;
    private Canvas mcanvas;
    private Bitmap mbitmap;
    private Bitmap bitmap;
    private int lastx;
    private int lasty;


    public G(Context context) {
        super(context);
        initview();
    }

    public G(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        initview();
    }

    public G(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initview();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width=getMeasuredWidth();
        int height=getMeasuredHeight();
        mbitmap=Bitmap.createBitmap(width,height, Bitmap.Config.ALPHA_8);
        mcanvas=new Canvas(mbitmap);
       initpaint();
       //遮盖
        mcanvas.drawColor(Color.BLACK);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();

        //当前坐标
        int x = (int) event.getX();
        int y = (int) event.getY();
        //判断意图
        switch (action){
            case MotionEvent.ACTION_DOWN:
                lastx=x;
                lasty=y;
                mpath.moveTo(lastx,lasty);
                break;
            case MotionEvent.ACTION_MOVE:
                //坐标的值
                int absx = Math.abs(x-lastx);
                int absy = Math.abs(y-lasty);

                mpath.lineTo(x,y);

                lastx=x;
                lasty=y;
                break;
            case MotionEvent.ACTION_UP:

                break;
        }
        invalidate();
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(bitmap,0,0,null);
        drawPath();
        canvas.drawBitmap(mbitmap,0,0,null);
    }

    private void drawPath() {
        //模式
        paint_one.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
        mcanvas.drawPath(mpath,paint_one);
    }

    private void initpaint() {
        paint_one.setColor(Color.RED);
        paint_one.setAntiAlias(true);
        paint_one.setDither(true);
        //线条圆角
        paint_one.setStrokeJoin(Paint.Join.ROUND);
        paint_one.setStrokeCap(Paint.Cap.ROUND);
        paint_one.setStyle(Paint.Style.STROKE);
        //宽度
        paint_one.setStrokeWidth(20);
    }

    private void initview() {
        paint_one=new Paint();
        mpath=new Path();
        bitmap=BitmapFactory.decodeResource(getResources(),R.drawable.a);
    }
}