刮刮乐自定义view实现

利用图层混合原理实现简单的刮刮乐效果,
直接上演示效果

public class XfermodeEraserView extends View {
    private Bitmap mSrcB, mDstB, mTxtB;
    private Paint mPaint;
    private Path mPath;

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

    public XfermodeEraserView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public XfermodeEraserView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStrokeWidth(80);
        mPaint.setColor(Color.GREEN);
        mPaint.setStyle(Paint.Style.STROKE);

        //图层混合需要关闭硬件加速（Android默认开启硬件加速，api14之后某些图层混合功能不支持硬件加速）
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
		//读取本地图片到bitmap
        mSrcB = BitmapFactory.decodeResource(getResources(), R.drawable.eraser);
        mTxtB = BitmapFactory.decodeResource(getResources(), R.drawable.result);
        //创建一个显示图层混合后的bitmap
        mDstB = Bitmap.createBitmap(mSrcB.getWidth(), mSrcB.getHeight(), Bitmap.Config.ARGB_8888);

        //贝塞尔曲线路径
        mPath = new Path();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //绘制中奖结果
        canvas.drawBitmap(mTxtB, 0, 0, mPaint);

        //使用离屏绘制，防止背景影响图层混合结果
        int saveLayer = canvas.saveLayer(0, 0, getWidth(), getHeight(), mPaint, Canvas.ALL_SAVE_FLAG);

        //先将路径绘制到目标bitmap上
        Canvas dstCanvas = new Canvas(mDstB);
        dstCanvas.drawPath(mPath, mPaint);
        //绘制目标图像
        canvas.drawBitmap(mDstB, 0, 0, mPaint);
        //设置 模式 为 SRC_OUT, 擦橡皮区域为交集区域需要清掉像素
        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));

        //绘制源图像
        canvas.drawBitmap(mSrcB, 0, 0, mPaint);
        mPaint.setXfermode(null);
        //与canvas.saveLayer（）成对出现，将离屏缓存的内容显示在画布上
        canvas.restoreToCount(saveLayer);

    }
    private float mEventX, mEventY;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mEventX=event.getX();
                mEventY=event.getY();
                //将开始点移动到手指按下点
                mPath.moveTo(mEventX,mEventY);
                break;
            case MotionEvent.ACTION_MOVE:
                float endX=event.getX();
                float endY=event.getY();
                //画二次贝塞尔曲线
                mPath.quadTo(mEventX,mEventY,endX,endY);
                mEventX=event.getX();
                mEventY=event.getY();
                break;
        }
        //通过调用该方法达到调用onDraw（）方法的目的。
        invalidate();
        return true;
    }
}