實現目標

相信大家都知道毛玻璃效果是怎樣的，也可以說是高斯模糊效果。效果圖如下：
這是一個透明，且會對背景進行高斯模糊的效果，看起來就像是毛玻璃一樣，其實不光是側滑菜單，只要是view，理論上都可以實現這樣的效果，接下來我們就來實現這個效果。

第一步：框架搭建

我使用的android studio，所以要創建這樣一個帶側滑菜單的項目非常簡單，在新建項目的步驟中，執行到這一步，選擇Navigation Drawer Activity就可以了： 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"brush:java;">mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);這個NavigationDrawerFragment就是我們的側滑菜單實現的類，可以不去管它。 然後需要獲取到這個Fragment中的View，獲取View的觀察者並且注冊PreDraw監聽事件：

mNavigationDrawerFragment.getView().getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            
        });

這個OnPreDrawListener需要實現OnPreDraw方法，就在這個方法中，對當前的View，進行截圖，並且高斯模糊。 首先找到根控件，並創建一個Bitmap對象來保存截圖。

private FrameLayout view;
private Bitmap bitmap;

對view初始化後，開始對view進行截圖，對view截圖的方式如下：

view.buildDrawingCache();
bitmap = view.getDrawingCache();

這樣，bitmap中就保存了當前的view的截圖，接下來我們要對圖片進行高斯模糊，關於高斯模糊的算法，網上有很多，我就隨便貼一個（復制來的）：

    public static Bitmap doBlur(Bitmap sentBitmap, int radius, boolean canReuseInBitmap) {

        // Stack Blur v1.0 from
        // http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
        //
        // Java Author: Mario Klingemann 
        // http://incubator.quasimondo.com
        // created Feburary 29, 2004
        // Android port : Yahel Bouaziz 
        // http://www.kayenko.com
        // ported april 5th, 2012

        // This is a compromise between Gaussian Blur and Box blur
        // It creates much better looking blurs than Box Blur, but is
        // 7x faster than my Gaussian Blur implementation.
        //
        // I called it Stack Blur because this describes best how this
        // filter works internally: it creates a kind of moving stack
        // of colors whilst scanning through the image. Thereby it
        // just has to add one new block of color to the right side
        // of the stack and remove the leftmost color. The remaining
        // colors on the topmost layer of the stack are either added on
        // or reduced by one, depending on if they are on the right or
        // on the left side of the stack.
        //
        // If you are using this algorithm in your code please add
        // the following line:
        //
        // Stack Blur Algorithm by Mario Klingemann 

        Bitmap bitmap;
        if (canReuseInBitmap) {
            bitmap = sentBitmap;
        } else {
            bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);
        }

        if (radius < 1) {
            return (null);
        }

        int w = bitmap.getWidth();
        int h = bitmap.getHeight();

        int[] pix = new int[w * h];
        bitmap.getPixels(pix, 0, w, 0, 0, w, h);

        int wm = w - 1;
        int hm = h - 1;
        int wh = w * h;
        int div = radius + radius + 1;

        int r[] = new int[wh];
        int g[] = new int[wh];
        int b[] = new int[wh];
        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
        int vmin[] = new int[Math.max(w, h)];

        int divsum = (div + 1) >> 1;
        divsum *= divsum;
        int dv[] = new int[256 * divsum];
        for (i = 0; i < 256 * divsum; i++) {
            dv[i] = (i / divsum);
        }

        yw = yi = 0;

        int[][] stack = new int[div][3];
        int stackpointer;
        int stackstart;
        int[] sir;
        int rbs;
        int r1 = radius + 1;
        int routsum, goutsum, boutsum;
        int rinsum, ginsum, binsum;

        for (y = 0; y < h; y++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            for (i = -radius; i <= radius; i++) {
                p = pix[yi + Math.min(wm, Math.max(i, 0))];
                sir = stack[i + radius];
                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);
                rbs = r1 - Math.abs(i);
                rsum += sir[0] * rbs;
                gsum += sir[1] * rbs;
                bsum += sir[2] * rbs;
                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }
            }
            stackpointer = radius;

            for (x = 0; x < w; x++) {

                r[yi] = dv[rsum];
                g[yi] = dv[gsum];
                b[yi] = dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (y == 0) {
                    vmin[x] = Math.min(x + radius + 1, wm);
                }
                p = pix[yw + vmin[x]];

                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[(stackpointer) % div];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi++;
            }
            yw += w;
        }
        for (x = 0; x < w; x++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            yp = -radius * w;
            for (i = -radius; i <= radius; i++) {
                yi = Math.max(0, yp) + x;

                sir = stack[i + radius];

                sir[0] = r[yi];
                sir[1] = g[yi];
                sir[2] = b[yi];

                rbs = r1 - Math.abs(i);

                rsum += r[yi] * rbs;
                gsum += g[yi] * rbs;
                bsum += b[yi] * rbs;

                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }

                if (i < hm) {
                    yp += w;
                }
            }
            yi = x;
            stackpointer = radius;
            for (y = 0; y < h; y++) {
                // Preserve alpha channel: ( 0xff000000 & pix[yi] )
                pix[yi] = (0xff000000 & pix[yi]) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (x == 0) {
                    vmin[y] = Math.min(y + r1, hm) * w;
                }
                p = x + vmin[y];

                sir[0] = r[p];
                sir[1] = g[p];
                sir[2] = b[p];

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[stackpointer];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi += w;
            }
        }

        bitmap.setPixels(pix, 0, w, 0, 0, w, h);

        return (bitmap);
    }

第一個參數為需要高斯模糊的圖片，第二個參數可以理解為模糊效果大小，第三個參數表示位圖是否可以重復使用。 好了，有了處理好的圖片，就可以設置到Drawer的背景裡了。 。。。 真的嗎？ 仔細一想，當然不對，現在截的圖是整個view的圖，而我們的Drawer是慢慢側滑出來的，隨時都可能停止，所以，使用完整的圖肯定是不行的。 那麼就需要計算出截取view的圖片的位置，和設置到Drawer的位置，具體可以參考下圖：
從圖上可以看的出來，其中需要的參數都是有聯系的，也就是說，只要能得到其中的一個參數，其他的就能同時拿到了。 Drawer的寬度可以定死，例子中定的是240，現在就只需要獲取到側滑到哪一個位置就能夠算出所有的參數。 在View中，有這樣一個方法，叫做getLocationInWindow，可以獲取到當前View在整個Window中的位置，可以想象的到，獲取到的肯定是一個負數，通過Drawer的寬度和這個負數，可以很簡單的算出來顯示的寬度。（View中除了getLocationInWindow，還有很多其他的方法，獲取相對於各種視圖的位置，大家可以研究一下）。
首先獲取到位置：

int[] location = new int[2];
mNavigationDrawerFragment.getView().getLocationInWindow(location);
blur(bitmap, listView, location[0]);//只傳x坐標

blur函數就是我們處理位置的細節了，傳的listView是Fragment裡的唯一一個view：

    private void blur(Bitmap bkg, View view,int width) {
        float scaleFactor = 4;//縮放圖片，縮放之後模糊效果更好
        float radius = 2;

        Bitmap overlay = Bitmap.createBitmap((int) (view.getMeasuredWidth()/scaleFactor),
                (int) (view.getMeasuredHeight()/scaleFactor), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(overlay);
        canvas.translate(-view.getLeft()/scaleFactor, -view.getTop()/scaleFactor);
        canvas.scale(1 / scaleFactor, 1 / scaleFactor);
        Paint paint = new Paint();
        paint.setFlags(Paint.FILTER_BITMAP_FLAG);
        float visibleWidth = slideMenuWidth +width;//可見寬
        int visibleHeight = view.getHeight();//可見高
        //從view的截圖中截取的區域，+10和下面-10的原因是，高斯模糊的邊有時會有黑影，所以增大模糊區域
        Rect src = new Rect(0,0, (int)(visibleWidth)+10, visibleHeight);        
        RectF dest = new RectF(-width - 10, 0, slideMenuWidth, visibleHeight);//設置Drawer背景的區域                
        canvas.drawBitmap(bkg, src, dest, paint);        
        overlay = ImageUtils.doBlur(overlay, (int)radius, true);//進行高斯模糊操作        
        if (Build.VERSION.SDK_INT < 16) {//16level以前使用這個方法，在16中被廢棄                     
            view.setBackgroundDrawable(new BitmapDrawable(getResources(), overlay));        
        } else {            
            view.setBackground(new BitmapDrawable(getResources(), overlay));        
        }    
    }

整個的事件監聽代碼如下：

mNavigationDrawerFragment.getView().getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            @Override
            public boolean onPreDraw() {
                if (bitmap == null) {
                    view.buildDrawingCache();
                    bitmap = view.getDrawingCache();
                }
                int[] location = new int[2];
                mNavigationDrawerFragment.getView().getLocationInWindow(location);
                blur(bitmap, listView, location[0]);//只傳x坐標
                return true;
            }
        });

到這裡，側滑菜單的毛玻璃效果就已經完成了。

結語

如果能夠理解我上面使用的方法，我相信大家一定能夠舉一反三，實現所有view的毛玻璃效果，這個例子的代碼，我會放到github上，這裡就是鏈接地址：https://github.com/xjyaikj/GlassSlideMenuSample，如果代碼有什麼不對，或者值得優化的地方，非常希望您能跟我交流，我的聯系方式在左邊個人資料的下面。