Android高斯模糊实现(非原创)

高斯模糊能够很好的增加图片的美感，在实际开发中使用的比较多，这里提供了三种方式实现这种效果。

RenderScript实现

RenderScript是Android3.0中引入的，用来在Android上编写高性能代码的一种语言（使用C99标准）。
实现高斯模糊的核心代码：

private void applyBlur() {
    image.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {

        @Override
        public boolean onPreDraw() {
            image.getViewTreeObserver().removeOnPreDrawListener(this);
            image.buildDrawingCache();
            Bitmap bmp = image.getDrawingCache();
            blur(bmp, text);
            return true;
        }
    });
}

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
private void blur(Bitmap bkg, View view) {
    long startMs = System.currentTimeMillis();
    float radius = 20;

    Bitmap overlay = Bitmap.createBitmap((int)(view.getMeasuredWidth()), (int)(view.getMeasuredHeight()), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(overlay);
    canvas.translate(-view.getLeft(), -view.getTop());
    canvas.drawBitmap(bkg, 0, 0, null);

    RenderScript rs = RenderScript.create(SecondActivity.this);

    Allocation overlayAlloc = Allocation.createFromBitmap(rs, overlay);
    ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, overlayAlloc.getElement());
    blur.setInput(overlayAlloc);
    blur.setRadius(radius);
    blur.forEach(overlayAlloc);
    overlayAlloc.copyTo(overlay);
    view.setBackground(new BitmapDrawable(getResources(), overlay));
    rs.destroy();

    LogUtil.d("cost " + (System.currentTimeMillis() - startMs) + "ms");
}

当ImageView开始加载背景图时，取出它的drawableCache，进行blur处理，Gaussian blur的主要逻辑在blur函数中。对于在Java中使用RenderScript，文档中也有详细描述，对应到我们的代码，步骤为：

• 初始化一个RenderScript Context.
• 至少创建一个Allocation对象用于存储需要处理的数据.
• 创建compute kernel的实例，本例中是内置的ScriptIntrinsicBlur对象.
• 设置ScriptIntrinsicBlur实例的相关属性，包括Allocation, radius等.
• 开始blur操作，对应（forEach）.
• 将blur后的结果拷贝回bitmap中。

使用RenderScript存在兼容性的问题，但是性能是非常高的，在API-17以下使用需要导入RenderScript-v8兼容包，暂还试过低版本的兼容，有兴趣的可以谷歌一下。

FastBlur实现

FastBlur实现的核心代码如下:

import android.graphics.Bitmap;

/**
 * Created by Van Gogh on 2016/8/29.
 *
 * 高斯模糊算法
 */
public class FastBlur {

    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 <mario at quasimondo.com>
        // http://incubator.quasimondo.com
        // created Feburary 29, 2004
        // Android port : Yahel Bouaziz <yahel at kayenko.com>
        // 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 <mario@quasimondo.com>

        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);
    }
}

blur方法：

/**
* 一个高斯模糊的算法
*
* 可以对View的背景或者ViewGroup进行模糊,使用了过期的API
*
* @param bkg
* @param view
*/
private void blur(Bitmap bkg, View view) {
    long startMs = System.currentTimeMillis();
    float radius = 20;

    Bitmap overlay = Bitmap.createBitmap((int)(view.getMeasuredWidth()), (int)(view.getMeasuredHeight()), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(overlay);
    canvas.translate(-view.getLeft(), -view.getTop());
    canvas.drawBitmap(bkg, 0, 0, null);
    overlay = FastBlur.doBlur(overlay, (int)radius, true);
    view.setBackground(new BitmapDrawable(getResources(), overlay));
    LogUtil.d("cost " + (System.currentTimeMillis() - startMs) + "ms");
}

applyBlur方法：

/**
 * 添加模糊效果
 */
private void applyBlur() {
    imgBackground.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            imgBackground.getViewTreeObserver().removeOnPreDrawListener(this);
            imgBackground.buildDrawingCache();
            Bitmap bmp = imgBackground.getDrawingCache();
            blur(bmp, imgBackground);//imgBackground替换成需要设置背景模糊的View或ViewGroup
            return true;
        }
    });
}

AdvancedFastBlur实现

AdvancedFastBlur同样是使用FastBlur实现的,原理为先通过缩小图片，使其丢失一些像素点，接着进行模糊化处理，然后再放大到原来尺寸。由于图片缩小后再进行模糊处理，需要处理的像素点和半径都变小，从而使得模糊处理速度加快。代码如下：

/**
 * 一个高斯模糊的算法
 *
 * 可以对View的背景或者ViewGroup进行模糊,使用了过期的API
 *
 * @param bkg
 * @param view
 */
private void blur(Bitmap bkg, View view) {
    long startMs = System.currentTimeMillis();
    float radius = 2;//这个比FastBlur中的要小
    float scaleFactor = 8;//缩小比例

    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);
    canvas.drawBitmap(bkg, 0, 0, paint);
    overlay = FastBlur.doBlur(overlay, (int)radius, true);
    /*
       view.setBackgroundDrawable(Drawable);//只支持api16以上
     */
    view.setBackgroundDrawable(new BitmapDrawable(mContext.getResources(), overlay));
    LogUtil.d("cost " + (System.currentTimeMillis() - startMs) + "ms");
}

applyBlur方法和FastBlur对象与FastBlur实现中的相同。效率要高于FastBlur。

注意

由于FastBlur是将整个bitmap拷贝到一个临时的buffer中进行像素点操作，因此，它不适合处理一些过大的背景图，会容易导致OOM。