Android(安卓)preview YUV转换 RenderScript 优化

PS：2018/0807

不可以使用生产者模式去不断的textureView.getBitmap, 否则RenderThread线程会非常奇怪的抛出异常（疑似当前Frame被释放，再get的native层空指针）。应该在TextureView.SurfaceTextureListener的onSurfaceTextureUpdated(SurfaceTexture surface) 回调内去textureView.getBitmap

PS：2018/05/07

最近又发现TextureView的getBitmap方法更快，比RenderScript还快。具体就是讲Camera 的Preview set到TextureView上，然后调用TextureView的getBitmap方法。推荐用生产者模式去getBitmap，我试验的是整幅图也就10+ms

Context

YUV格式转换为Bitmap比较耗时，使用RenderScript从50ms降到3、4ms（和像素值、手机相关，但比例差不多）

RenderScript耗时的地方是内存Allocation的分配，RenderScript的初始化，所以要设置为属性缓存起来，不要重复创建。只要预览的宽高不变是不用变Allocation的大小的。

RenderScript

简单讲就是 Android系统为解决高计算作业问题采用了基于 C语言风格的RenderScript。具体：系统利用GPU、CPU多核来处理并发调度，使程序员只专注于算法。系统自己提供了几个常用的RenderScript，高斯模糊、直方图、yuv格式转换。

具体怎么看官网，不累述了，直接上代码

参考博客： Camera使用RenderScript

代码

    private void initRenderScript() {        renderScript = RenderScript.create(this);        yuvToRgbIntrinsic = ScriptIntrinsicYuvToRGB.create(renderScript, Element.U8_4(renderScript));        script = new ScriptC_rotator(renderScript);    }

    public Bitmap YUV_toRGB(byte[] yuvByteArray, int width, int height) {        Allocation in = getYuvAllocationIn(yuvByteArray);        Allocation out = getAllocationOut(width, height);        in.copyFrom(yuvByteArray);        yuvToRgbIntrinsic.setInput(in);        yuvToRgbIntrinsic.forEach(out);        Bitmap bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);        out.copyTo(bmp);        bmp = rotate(bmp);        return bmp;    }

    private Allocation getYuvAllocationIn(byte[] yuvByteArray) {        if (mInAllocation == null || yuvByteArray.length != preYuvInLength) {            preYuvInLength = yuvByteArray.length;            Type.Builder yuvType = new Type.Builder(renderScript, Element.U8(renderScript)).setX(yuvByteArray.length);            mInAllocation =  Allocation.createTyped(renderScript, yuvType.create(), Allocation.USAGE_SCRIPT);        }        return mInAllocation;    }

    private Allocation getAllocationOut(int W, int H) {        if (preW != W || preH != H) {            preW = W;            preH = H;            Type.Builder rgbaType = new Type.Builder(renderScript, Element.RGBA_8888(renderScript)).setX(W).setY(H);            outAllocation = Allocation.createTyped(renderScript, rgbaType.create(), Allocation.USAGE_SCRIPT);        }        return outAllocation;    }

    public Bitmap rotate(Bitmap bitmap) {        Bitmap.Config config = bitmap.getConfig();        int targetHeight = bitmap.getWidth();        int targetWidth = bitmap.getHeight();        script.set_inWidth(bitmap.getWidth());        script.set_inHeight(bitmap.getHeight());        Allocation sourceAllocation = getFromRotateAllocation(bitmap);        sourceAllocation.copyFrom(bitmap);        script.set_inImage(sourceAllocation);        bitmap.recycle();        Bitmap target = Bitmap.createBitmap(targetWidth, targetHeight, config);        final Allocation targetAllocation = getToRotateAllocation(target);        script.forEach_rotate_270_clockwise(targetAllocation, targetAllocation);        targetAllocation.copyTo(target);        return target;    }

    private Allocation getFromRotateAllocation(Bitmap bitmap) {        int targetHeight = bitmap.getWidth();        int targetWidth = bitmap.getHeight();        if (targetHeight != preRotateHeight || targetWidth != preRotateWidth) {            preRotateHeight = targetHeight;            preRotateWidth = targetWidth;            fromRotateAllocation = Allocation.createFromBitmap(renderScript, bitmap,                    Allocation.MipmapControl.MIPMAP_NONE,                    Allocation.USAGE_SCRIPT);        }        return fromRotateAllocation;    }    private Allocation getToRotateAllocation(Bitmap bitmap) {        int targetHeight = bitmap.getWidth();        int targetWidth = bitmap.getHeight();        if (targetHeight != preRotateHeight || targetWidth != preRotateWidth) {            toRotateAllocation =  Allocation.createFromBitmap(renderScript, bitmap,                    Allocation.MipmapControl.MIPMAP_NONE,                    Allocation.USAGE_SCRIPT);        }        return toRotateAllocation;    }

Preview拿的是物理设备方向，所以用时需要旋转，旋转的RenderScript是自己写的。

main/rs/your.package.name(包名)/rotate.rs

#pragma version(1)#pragma rs java_package_name(your.package.name)rs_allocation inImage;int inWidth;int inHeight;uchar4 __attribute__ ((kernel)) rotate_90_clockwise (uchar4 in, uint32_t x, uint32_t y) {    uint32_t inX  = inWidth - 1 - y;    uint32_t inY = x;    const uchar4 *out = rsGetElementAt(inImage, inX, inY);    return *out;}uchar4 __attribute__ ((kernel)) rotate_270_clockwise (uchar4 in, uint32_t x, uint32_t y) {    uint32_t inX = y;    uint32_t inY = inHeight - 1 - x;    const uchar4 *out = rsGetElementAt(inImage, inX, inY);    return *out;}

#pragma rs java_package_name(your.package.name) 这一行里的your.package.name需要替换你放置rotate.rs的地方

build后系统自动生成ScriptC_rotator 类，上文的script就是ScriptC_rotator的对象

RenderScript

代码

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