android 自定义控件canvas，画笔设置成透明，每次画笔移动造成图层叠加的效果

Azings 2016-12-19 12:08:26

我现在想做一个蒙版区域选择的功能，有两个canvas，一个用来放背景图片，另一个做蒙版的效果，做蒙版的时候用到两支画笔，一直用来做透明的背景，属性设置成#66666666，另一只画笔作为两支笔的交接区域的判断，两支画笔之间交叉画图的方式是XOR，现在的问题是，我在界面上触摸事，虽然两支画笔之间的交接的地方空白了，但是每一次点一下，作为透明模板的颜色就会加深一部分，就好像有两个背景叠加一样。

private int width;

    private int height;

    private Bitmap mBitmap;

    private Paint mPaintCircel;

    private Paint mPaintRect;

    private Canvas canvasBit;

    private Bitmap mBitmapBackground;

    private Bitmap mBitmapBackground1;

    private Matrix matrix;

    public boolean isfirstpaint = true;



    public MyBitmapTwo(Context context) {

        super(context);

    }



    public MyBitmapTwo(Context context, AttributeSet attrs) {

        super(context, attrs);



        path = new Path();

        

        mBitmapBackground = ((BitmapDrawable) getBackground()).getBitmap();



        matrix = new Matrix();

        mPaintCircel = new Paint();

        mPaintCircel.setColor(Color.parseColor("#00000000"));

        mPaintCircel.setAlpha(0);

        mPaintRect = new Paint();

        mPaintRect.setColor(Color.parseColor("#666666"));

        mPaintRect.setAlpha(80);

        PorterDuffXfermode mode = new PorterDuffXfermode(PorterDuff.Mode.XOR);//交叉的部分显示背景

        mPaintCircel.setXfermode(mode);

        mPaintCircel.setStrokeJoin(Paint.Join.ROUND);//设置线段中间用圆形填充

        mPaintCircel.setStrokeCap(Paint.Cap.ROUND);//设置线段开头是圆形

        mPaintCircel.setStrokeWidth(100);

        mPaintCircel.setStyle(Paint.Style.FILL_AND_STROKE);//非空心

        mPaintCircel.setPathEffect(new CornerPathEffect(360));

        mPaintCircel.setAntiAlias(true);//消锯齿



    }



    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

        setMeasuredDimension(width, height);//设置画布的大小，长和宽

        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);

        canvasBit = new Canvas(mBitmap);



    }



    @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

        canvas.drawBitmap(mBitmapBackground, new Rect(0, 0, mBitmapBackground.getWidth(), mBitmapBackground.getHeight()), new Rect(0, 0, width, height), null);//用图片做背景

        canvasBit.drawPath(path, mPaintCircel);//按路径画图形，

        canvasBit.drawRect(0, 0, width, height, mPaintRect);//跟view大小一样的透明背景

        canvas.drawBitmap(mBitmap, 0, 0, null);

    }



    float x;

    float y;

    float old_x;

    float old_y;

    private Path path;



    @Override//点击事件

    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {

            case MotionEvent.ACTION_DOWN:

                x = event.getX();

                y = event.getY();

                path.moveTo(x, y);

                invalidate();

                old_x = x;

                old_y = y;

                return true;

            case MotionEvent.ACTION_MOVE:

                x = event.getX();

                y = event.getY();

                path.moveTo(old_x, old_y);

                path.lineTo(x, y);

                invalidate();

                old_x = x;

                old_y = y;

                return true;

        }

        return super.onTouchEvent(event);

    }