转自：https://ligboy.org/?p=380

对于不需要看废话的请直接Show me the code

对于模糊处理，一般的解决方案有四种:

1. Java实现的算法处理；
2. NDK实现的算法处理；
3. RenderScript处理；
4. openGL处理；

这四种方案的性能考虑的话，一般来讲应该是： 1 < 3 ＜ 2  < 4 (2、3的性能非常接近)，不过当属RenderScript方式最为简便（很显然嘛，平台无关性）。

RenderScript是Android自SDK17提供的一套平台无关计算密集脚本，它使用C99语法脚本，可以实现高性能的计算，而其包含大量内联函数，其中就包括了我们今天用到的：ScriptIntrinsicBlur，这是一个高斯模糊处理内联函数，一般系统用来进行阴影的计算处理。

上面有提到RenderScript是自SDK17引入的，但是Android 团队为我们提供了RenderScript support library，而起在Gradle-base的项目中的引入也极其简单，仅需要在module build.gradle设置以下11、12两行即可：

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"
 
    defaultConfig {
        applicationId "org.ligboy.backsound"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
        renderscriptTargetApi 20
        renderscriptSupportModeEnabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

接下来简单说说 ScriptIntrinsicBlur，使用它虽然很方便，但是也是有弊端的，模糊radius不能超过25.0f，不过我们可以通过缩小原图抽样的方式变相的进行扩大半径。

Glide是一个优秀的图片加载缓存处理等一系列功能的框架，它优雅而且使用渐变，扩展也很容易，Glide就提供了自定义Transformation的方式进行扩展图片的处理

到了这里就是通过自定义Transformation的方式，详细的这里就不赘述了，感兴趣可以查看Glide官方文档：Transformation。需要特别提到的是，每个Transformation都有一个String getId()的回调，该ID用于在对处理后的图片进行缓存时的文件命名，这样当下次相同图片使用相同Transformation时，则无需任何实际处理，直接读取缓存文件，所以我们实现时的ID需要同时关联所有的调整参数，参数改变的ID也应该相应改变。下面就是我自定义的BlurTransformation

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffColorFilter;
import android.support.annotation.FloatRange;
import android.support.v8.renderscript.Allocation;
import android.support.v8.renderscript.Element;
import android.support.v8.renderscript.RenderScript;
import android.support.v8.renderscript.ScriptIntrinsicBlur;

import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
import com.bumptech.glide.load.resource.bitmap.BitmapTransformation;
import com.bumptech.glide.request.target.Target;

/**
 * Georgia Blur Transformation
 * <p>
 * @author Ligboy.Liu ligboy@gmail.com.
 */
public class BlurTransformation extends BitmapTransformation {

    private static final String ID = "org.ligboy.glide.BlurTransformation";

    public static final float DEFAULT_RADIUS = 25.0f;
    public static final float MAX_RADIUS = 25.0f;
    private static final float DEFAULT_SAMPLING = 1.0f;

    private Context mContext;
    private float mSampling = DEFAULT_SAMPLING;
    private float mRadius;
    private int mColor;

    public static class Builder {

        private Context mContext;
        private float mRadius = DEFAULT_RADIUS;
        private int mColor = Color.TRANSPARENT;

        public Builder(Context mContext) {
            this.mContext = mContext;
        }

        public float getRadius() {
            return mRadius;
        }

        public Builder setRadius(float radius) {
            mRadius = radius;
            return this;
        }

        public int getColor() {
            return mColor;
        }

        public Builder setColor(int color) {
            mColor = color;
            return this;
        }

        public BlurTransformation build() {
            return new BlurTransformation(mContext, mRadius, mColor);
        }

    }

    /**
     *
     * @param context Context
     * @param radius The blur's radius.
     * @param color The color filter for blurring.
     */
    public BlurTransformation(Context context, @FloatRange(from = 0.0f) float radius, int color) {
        super(context);
        mContext = context;
        if (radius > MAX_RADIUS) {
            mSampling = radius / 25.0f;
            mRadius = MAX_RADIUS;
        } else {
            mRadius = radius;
        }
        mColor = color;
    }
    /**
     *
     * @param context Context
     * @param radius The blur's radius.
     */
    public BlurTransformation(Context context, @FloatRange(from = 0.0f) float radius) {
        this(context, radius, Color.TRANSPARENT);
    }

    public BlurTransformation(Context context) {
        this(context, DEFAULT_RADIUS);
    }

    /**
     * Transforms the given {@link Bitmap} based on the given dimensions and returns the transformed
     * result.
     * <p/>
     * <p>
     * The provided Bitmap, toTransform, should not be recycled or returned to the pool. Glide will automatically
     * recycle and/or reuse toTransform if the transformation returns a different Bitmap. Similarly implementations
     * should never recycle or return Bitmaps that are returned as the result of this method. Recycling or returning
     * the provided and/or the returned Bitmap to the pool will lead to a variety of runtime exceptions and drawing
     * errors. See #408 for an example. If the implementation obtains and discards intermediate Bitmaps, they may
     * safely be returned to the BitmapPool and/or recycled.
     * </p>
     * <p/>
     * <p>
     * outWidth and outHeight will never be {@link Target#SIZE_ORIGINAL}, this
     * class converts them to be the size of the Bitmap we're going to transform before calling this method.
     * </p>
     *
     * @param pool        A {@link BitmapPool} that can be used to obtain and
     *                    return intermediate {@link Bitmap}s used in this transformation. For every
     *                    {@link Bitmap} obtained from the pool during this transformation, a
     *                    {@link Bitmap} must also be returned.
     * @param toTransform The {@link Bitmap} to transform.
     * @param outWidth    The ideal width of the transformed bitmap (the transformed width does not need to match exactly).
     * @param outHeight   The ideal height of the transformed bitmap (the transformed heightdoes not need to match
     */
    @Override
    protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
        boolean needScaled = mSampling == DEFAULT_SAMPLING;
        int originWidth = toTransform.getWidth();
        int originHeight = toTransform.getHeight();
        int width, height;
        if (needScaled) {
            width = originWidth;
            height = originHeight;
        } else {
            width = (int) (originWidth / mSampling);
            height = (int) (originHeight / mSampling);
        }
        //find a re-use bitmap
        Bitmap bitmap = pool.get(width, height, Bitmap.Config.ARGB_8888);
        if (bitmap == null) {
            bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        }

        Canvas canvas = new Canvas(bitmap);
        if (mSampling != DEFAULT_SAMPLING) {
            canvas.scale(1 / mSampling, 1 / mSampling);
        }
        Paint paint = new Paint();
        paint.setFlags(Paint.FILTER_BITMAP_FLAG | Paint.ANTI_ALIAS_FLAG);
        PorterDuffColorFilter filter =
                new PorterDuffColorFilter(mColor, PorterDuff.Mode.SRC_ATOP);
        paint.setColorFilter(filter);
        canvas.drawBitmap(toTransform, 0, 0, paint);
// TIPS: Glide will take care of returning our original Bitmap to the BitmapPool for us,
// we needn't to recycle it. 
//        toTransform.recycle();  <--- Just for tips. by Ligboy

        RenderScript rs = RenderScript.create(mContext);
        Allocation input = Allocation.createFromBitmap(rs, bitmap, Allocation.MipmapControl.MIPMAP_NONE,
                Allocation.USAGE_SCRIPT);
        Allocation output = Allocation.createTyped(rs, input.getType());
        ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));

        blur.setInput(input);
        blur.setRadius(mRadius);
        blur.forEach(output);
        output.copyTo(bitmap);

        rs.destroy();

        if (needScaled) {
            return bitmap;
        } else {
            Bitmap scaled = Bitmap.createScaledBitmap(bitmap, originWidth, originHeight, true);
            bitmap.recycle();
            return scaled;
        }
    }

    /**
     * A method to get a unique identifier for this particular transformation that can be used as part of a cache key.
     * The fully qualified class name for this class is appropriate if written out, but getClass().getName() is not
     * because the name may be changed by proguard.
     * <p/>
     * <p>
     * If this transformation does not affect the data that will be stored in cache, returning an empty string here
     * is acceptable.
     * </p>
     *
     * @return A string that uniquely identifies this transformation.
     */
    @Override
    public String getId() {
        StringBuilder sb = new StringBuilder(ID);
        sb
                .append('-').append(mRadius)
                .append('-').append(mColor);
        return sb.toString();
    }
}

使用起来也是非常简单：

Glide.with(MainActivity.this).load(imageFile.getUrl())
         .transform(new BlurTransformation(MainActivity.this, 100))
         .crossFade()
         .into(mBackgroundImageView);