Android 图片高级绘图效果---高斯模糊

高斯模糊就是将指定像素变换为其与周边像素加权平均后的值，权重就是高斯分布函数计算出来的值。高斯模糊能够将图片制作成类似磨砂的图片效果，一般这些图片都用来作为背景。

目前使用到的是RenderScript ，其特点是使用起来比较方便，虽然效率不是很高，但是也能够满足目前的使用。使用流程如下：

1. 添加混淆配置

-keepclasseswithmembernames class * {
    native <methods>;
}
-keep class android.support.v8.renderscript.** { *; }

2.使用高斯模糊

private void blur(Bitmap bkg, View view) {

        float radius = 25;

        Bitmap overlay = Bitmap.createBitmap((int) (view.getMeasuredWidth()), (int) (view.getMeasuredHeight()), Bitmap.Config.ARGB_8888);

        float scaleW = (float) view.getMeasuredWidth() / (float) bkg.getWidth();
        float scaleH = (float) view.getMeasuredHeight() / (float) bkg.getHeight();

        Matrix matrix = new Matrix();
        matrix.postScale(scaleW, scaleH);
        Bitmap resizeBmp = Bitmap.createBitmap(bkg, 0, 0, bkg.getWidth(), bkg.getHeight(), matrix, true);

        Canvas canvas = new Canvas(overlay);

        canvas.translate(-view.getLeft(), -view.getTop());
        canvas.drawBitmap(resizeBmp, 0, 0, null);

        RenderScript rs = RenderScript.create(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();
    }