Android實現(xiàn)電子書放大鏡效果

public class MagnifierLayout extends FrameLayout {    private Bitmap mBitmap;    private Paint mPaintShadow,mPaintBitmap;    private long mShowTime = 0;//用于判斷顯示放大鏡的時間    private boolean mIsShowMagnifier = false;//是否顯示放大鏡    private Path mPath;//用于裁剪畫布的路徑    private float mShowMagnifierX = 0;//顯示放大鏡的X坐標(biāo)    private float mShowMagnifierY = 0;//顯示放大鏡的Y坐標(biāo)    private float mMagnifierRadius = 200;//放大鏡的半徑    private float mScaleRate = 3f;//放大比例    private Handler mHandler = new Handler();    private Runnable mRunnable = new Runnable() {        @Override        public void run() {            mIsShowMagnifier = true;            postInvalidate();        }    };    public MagnifierLayout(@NonNull Context context) {        this(context,null);    }
    public MagnifierLayout(@NonNull Context context, @Nullable AttributeSet attrs) {        this(context, attrs,0);    }
    public MagnifierLayout(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        init();    }
    private void init(){        //繪制放大鏡邊緣投影的畫筆        mPaintShadow = new Paint(Paint.ANTI_ALIAS_FLAG);        //設(shè)置放大鏡邊緣的投影        mPaintShadow.setShadowLayer(20,6,6, Color.BLACK);        //繪制Bitmap的畫筆        mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG);        mPath = new Path();        setLayerType(View.LAYER_TYPE_SOFTWARE, null);    }
    @Override    public boolean onTouchEvent(MotionEvent event) {        switch (event.getAction()){            case MotionEvent.ACTION_DOWN:                mShowTime = System.currentTimeMillis();                mShowMagnifierX = event.getX() + mMagnifierRadius;                mShowMagnifierY = event.getY() - mMagnifierRadius;                //如果持續(xù)按超過一秒就顯示放大鏡                startShowMagnifierDelay();                break;            case MotionEvent.ACTION_MOVE:                //觸摸時間大于1秒才顯示                if(System.currentTimeMillis() - mShowTime >= 1000){                    stopShowMagnifier();                    mIsShowMagnifier = true;                    mShowMagnifierX = event.getX() + mMagnifierRadius;                    mShowMagnifierY = event.getY() - mMagnifierRadius;                    //重繪                    postInvalidate();                }                break;            case MotionEvent.ACTION_UP:                stopShowMagnifier();                mIsShowMagnifier = false;                postInvalidate();                break;        }        return true;    }
    private void startShowMagnifierDelay() {        stopShowMagnifier();        mHandler.postDelayed(mRunnable,1000);    }    private void stopShowMagnifier() {        mHandler.removeCallbacks(mRunnable);    }
    @Override    protected void dispatchDraw(Canvas canvas) {        if(mIsShowMagnifier){            //創(chuàng)建整個布局內(nèi)容的Bitmap            mBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);            Canvas mCanvas = new Canvas(mBitmap);            //將當(dāng)前布局的內(nèi)容繪制在Bitmap上            super.dispatchDraw(mCanvas);            //將Bitmap繪制出來(否則頁面是空白，因為上面是用我們自定義的Canvas進(jìn)行繪制的，因此我們還需要用系統(tǒng)的這個進(jìn)行繪制一遍)            canvas.drawBitmap(mBitmap,0,0,mPaintBitmap);            //繪制出放大鏡邊緣的投影            canvas.drawCircle(mShowMagnifierX,mShowMagnifierY,mMagnifierRadius,mPaintShadow);            canvas.save();            //計算出要裁剪畫布的圓形路徑            mPath.reset();            mPath.addCircle(mShowMagnifierX,mShowMagnifierY,mMagnifierRadius, Path.Direction.CW);            //將圓形路徑的畫布裁剪出來，這樣繪制的Bitmap就是圓形的            canvas.clipPath(mPath);            //繪制當(dāng)前布局的背景顏色，否則放大鏡顯示的背景會是黑色            getBackground().draw(canvas);            //根據(jù)縮放的比例計算出裁剪的Bitmap的最小寬高            float magnifierWidthAndHeight = mMagnifierRadius * 2 / mScaleRate;            //計算出該裁剪的區(qū)域(就是使手指所在的點在要裁剪的Bitmap的中央)，并進(jìn)行邊界值處理(開始裁剪的X點不能小于0和大于Bitmap的寬度，并且X點的位置加上要裁剪的寬度不能大于Bitmap的寬度，Y點也是一樣)            int cutX = Math.max((int) (mShowMagnifierX - mMagnifierRadius - magnifierWidthAndHeight / 2), 0);            int cutY = Math.min(Math.max((int) (mShowMagnifierY + mMagnifierRadius - magnifierWidthAndHeight / 2),0), mBitmap.getHeight());            //適配邊界值            int cutWidth = magnifierWidthAndHeight + cutX > mBitmap.getWidth() ? mBitmap.getWidth() - cutX : (int)magnifierWidthAndHeight;            int cutHeight = magnifierWidthAndHeight + cutY > mBitmap.getHeight() ? mBitmap.getHeight() - cutY : (int)magnifierWidthAndHeight;            mBitmap = Bitmap.createBitmap(mBitmap,cutX,cutY,cutWidth,cutHeight);            //將裁剪出來的區(qū)域放大            mBitmap = Bitmap.createScaledBitmap(mBitmap,(int) (mBitmap.getWidth() * mScaleRate),(int)(mBitmap.getHeight() * mScaleRate),true);            //繪制放大后的Bitmap，由于Bitmap的縮放是從左上點開始的因此還要根據(jù)縮放的比例進(jìn)行相應(yīng)的偏移展示            canvas.drawBitmap(mBitmap,mShowMagnifierX - mMagnifierRadius ,mShowMagnifierY - mMagnifierRadius,mPaintBitmap);            canvas.restore();            mBitmap.recycle();            mBitmap = null;        }else {            super.dispatchDraw(canvas);        }    }}