android tv 大背景图加载优化

android tv 有时候需要加载全屏背景图，且背景图也很大，特别是背景图是服务器下发的，下载好存在本地。加载的时候需要异步加载，这样异步加载的时候就会先显示的是Application的默认背景图（demo是黑屏图），然后才能加载到图片，为了提高这个背景图加载的用户体验，可以先读取这个图片的部分像素的小图，然后生成一张大尺寸高斯模糊图直接加载，这个时候比加载原始大图要快得多，在性能差的设备都基本可以达到直接显示出来的效果。

先看下直接加载的效果图

device-2019-10-17-174850.gif

如果不使用先读取小图的方式效果

device-2019-10-17-175140.gif

算法详解：

public static Drawable buildBlurDrawable(Context context, String filePath) throws Exception {
        BitmapFactory.Options opts = new BitmapFactory.Options();
        opts.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(filePath, opts);

        opts.inSampleSize = computeSampleSize(opts, -1, 64 * 64);
        opts.inJustDecodeBounds = false;
        opts.inPurgeable = true;
        opts.inInputShareable = true;
        opts.inPreferredConfig = Bitmap.Config.ARGB_4444;
        Bitmap mBitmap = BitmapFactory.decodeFile(filePath, opts);
        if(mBitmap.getWidth() > 0 && mBitmap.getHeight() > 0){
            Bitmap overlay = doBlurOnBackgournd(mBitmap);
            mBitmap.recycle();
            return new BitmapDrawable(context.getResources(), overlay);
        } else {
            mBitmap.recycle();
            return null;
        }
    }

先读取了64x64像素的小图，并且使用ARGB_4444的方式节省内存，加快读取速度，读取完这张小图后使用高斯模糊再转化成原来的大图，速度很快

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;

public class FastBlur {

    public static Drawable buildBlurDrawable(Context context, int resId) throws Exception {
        BitmapFactory.Options opts = new BitmapFactory.Options();
        opts.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(context.getResources(), resId, opts);

        opts.inSampleSize = computeSampleSize(opts, -1, 64 * 64);
        opts.inJustDecodeBounds = false;
        opts.inPurgeable = true;
        opts.inInputShareable = true;
        opts.inPreferredConfig = Bitmap.Config.ARGB_4444;
        Bitmap mBitmap = BitmapFactory.decodeResource(context.getResources(),
                resId, opts);
        if(mBitmap.getWidth() > 0 && mBitmap.getHeight() > 0){
            Bitmap overlay = doBlurOnBackgournd(mBitmap);
            mBitmap.recycle();
            return new BitmapDrawable(context.getResources(), overlay);
        } else {
            mBitmap.recycle();
            return null;
        }
    }

    public static Drawable buildBlurDrawable(Context context, String filePath) throws Exception {
        BitmapFactory.Options opts = new BitmapFactory.Options();
        opts.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(filePath, opts);

        opts.inSampleSize = computeSampleSize(opts, -1, 64 * 64);
        opts.inJustDecodeBounds = false;
        opts.inPurgeable = true;
        opts.inInputShareable = true;
        opts.inPreferredConfig = Bitmap.Config.ARGB_4444;
        Bitmap mBitmap = BitmapFactory.decodeFile(filePath, opts);
        if(mBitmap.getWidth() > 0 && mBitmap.getHeight() > 0){
            Bitmap overlay = doBlurOnBackgournd(mBitmap);
            mBitmap.recycle();
            return new BitmapDrawable(context.getResources(), overlay);
        } else {
            mBitmap.recycle();
            return null;
        }
    }

    public static Bitmap doBlurOnBackgournd(Bitmap sourceBitmap){
        float scaleFactor = 1;
        float radius = 5;
        return doBlur(sourceBitmap, scaleFactor, radius);
    }

    public static Bitmap doBlur(Bitmap sourceBitmap, float scaleFactor, float radius) {
        // long time1 = System.currentTimeMillis();
        Bitmap overlay = Bitmap.createBitmap(
                (int) (sourceBitmap.getWidth() / scaleFactor),
                (int) (sourceBitmap.getHeight() / scaleFactor),
                Bitmap.Config.ARGB_8888);

        Canvas canvas = new Canvas(overlay);

        // canvas.translate(-getLeft() / scaleFactor, -getTop() / scaleFactor);
        canvas.scale(1 / scaleFactor, 1 / scaleFactor);

        Paint paint = new Paint();
        paint.setFlags(Paint.FILTER_BITMAP_FLAG);
        canvas.drawBitmap(sourceBitmap, 0, 0, paint);

        overlay = FastBlur.doBlur(overlay, (int) radius, true);
        // long time2 = System.currentTimeMillis();
        // Log.i("Catch", "time doBlur:" + (time2 - time1));
        return overlay;
    }

    public static int computeSampleSize(BitmapFactory.Options options,
            int minSideLength, int maxNumOfPixels) {
        int initialSize = computeInitialSampleSize(options, minSideLength,
                maxNumOfPixels);
        int roundedSize;
        if (initialSize <= 8) {
            roundedSize = 1;
            while (roundedSize < initialSize) {
                roundedSize <<= 1;
            }
        } else {
            roundedSize = (initialSize + 7) / 8 * 8;
        }
        return roundedSize;
    }

    private static int computeInitialSampleSize(BitmapFactory.Options options,
            int minSideLength, int maxNumOfPixels) {
        double w = options.outWidth;
        double h = options.outHeight;
        int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math
                .sqrt(w * h / maxNumOfPixels));
        int upperBound = (minSideLength == -1) ? 128 : (int) Math.min(
                Math.floor(w / minSideLength), Math.floor(h / minSideLength));
        if (upperBound < lowerBound) {
            // return the larger one when there is no overlapping zone.
            return lowerBound;
        }
        if ((maxNumOfPixels == -1) && (minSideLength == -1)) {
            return 1;
        } else if (minSideLength == -1) {
            return lowerBound;
        } else {
            return upperBound;
        }
    }

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

        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);
    }
}

调用实现代码

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.widget.ImageView;

public class BackgroundActivity extends Activity {
    Bitmap bitmap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_back);

        final String imgPath = "";
        ImageView img1 = findViewById(R.id.img1);
        try {
            img1.setBackgroundDrawable(FastBlur.buildBlurDrawable(this, imgPath));
        } catch (Exception e) {
            e.printStackTrace();
        }
        new Thread() {
            public void run() {
                try {
                    bitmap = BitmapFactory.decodeFile(imgPath);
                } catch (Exception e) {
                    e.printStackTrace();
                }

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        ImageView img1 = findViewById(R.id.img1);
                        try {
                            img1.setImageBitmap(bitmap);
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                });
            }
        }.start();
    }

}

布局代码

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/img1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

这里使用ImageView实现的背景展示，实际加载可以使用自己项目中使用到的图片框架，比如我的项目中使用的是fresco加载的图片

public static void setDraweeBackground(Context context, SimpleDraweeView mBackgroundDrawee, String path, int width, int height) {
        Uri uri = UriUtil.parseUriOrNull("file://" + path);
        ImagePipeline imagePipeline = Fresco.getImagePipeline();
        if (!imagePipeline.isInBitmapMemoryCache(uri)) {
            try {
                mBackgroundDrawee.getHierarchy().setPlaceholderImage(FastBlur.buildBlurDrawable(context, path));
            } catch (Exception e) {
                //TODO set default background
                return;
            }
        }
        ImageRequest request = ImageRequestBuilder.newBuilderWithSource(uri)
                .setResizeOptions(new ResizeOptions(width, height)).build();
        DraweeController controller = Fresco.newDraweeControllerBuilder().setImageRequest(request)
                .setOldController(mBackgroundDrawee.getController()).build();
        mBackgroundDrawee.setController(controller);
    }

注意显示图片的时候还要注意裁剪图片到屏幕的合适尺寸，节省内存