TextureView.getBitmap()显示不一致的性能

Question

我正在使用从处理我的视频输入的TextureView获得的Bitmap图像进行一些图像处理测试.在我的测试中,我注意到TextureView.getBitmap(Bitmap)运行的时间,有时在执行之间有所不同.

为了演示这个问题,我修改了TextureView API 参考中的一个示例.在下面的代码中,我使用相机作为TextureView的输入,抓取位图并将其渲染到SurfaceView,测量它需要多少时间.我在一对运行Android 4.2.2的Nexus 7设备上进行了测试.我实际上注意到了两种模式,一种是慢速的,一种是快速的.

当执行"慢"时,getBitmap(Bitmap)大约需要20ms.当执行"快"时,getBitmap(Bitmap)大约需要15ms.

大多数情况下,这个应用程序以"慢"模式运行.如果我摆弄设备或重新编译/重新安装应用程序,有时我会让它以"快速"模式工作.但之后它将再次缓慢运行.速度仅在程序重新启动后才会更改,从不会在执行期间发生变化.

顺便说一句,将Bitmap转储到SurfaceView只需要大约8ms:我想知道为什么从TextureView中获取Bitmap需要花费的时间超过两倍.

问题:

1. 为什么执行时间的差异会发生？
2. 有没有办法确保getBitmap(Bitmap)始终尽可能快地运行？
3. 写入SurfaceView比从TextureView读取速度快两倍是否合理？

谢谢.

--Rafael

PS:我已经在Android开发者谷歌集团发布了这个,但它似乎自上周以来一直处于适度调整状态.抱歉交叉发布.

编辑:

我已经为GitHub 添加了一个示例项目,供那些希望更轻松地尝试它的人使用:

活动:

import java.io.IOException;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.SurfaceTexture;
import android.hardware.Camera;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.TextureView;

public class LiveCameraActivity extends Activity implements TextureView.SurfaceTextureListener {
    private Camera mCamera;
    private TextureView mTextureView;
    private SurfaceView mSurfaceView;

    private final int imgW = 640;
    private final int imgH = 480;
    private Bitmap bmp = Bitmap.createBitmap(imgW, imgH, Bitmap.Config.ARGB_8888);
    private Canvas canvas = new Canvas(bmp);
    private Paint paint1 = new Paint();
    private SurfaceHolder mSurfaceHolder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main2);

        mSurfaceView = (SurfaceView) findViewById(R.id.surfaceview);
        mSurfaceHolder = mSurfaceView.getHolder();

        mTextureView = (TextureView) findViewById(R.id.textureview);
        mTextureView.setSurfaceTextureListener(this);

        final int textSize = 24;
        paint1.setColor(0xff00ffff);
        paint1.setTextSize(textSize);

    }

    public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
        mCamera = Camera.open(Camera.getNumberOfCameras()-1);
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewSize(imgW, imgH);
        mCamera.setParameters(parameters);

        try {
            mCamera.setPreviewTexture(surface);
            mCamera.startPreview();
        } catch (IOException ioe) {
            // Something bad happened
        }
    }

    public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
        // Ignored, Camera does all the work for us
    }

    public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
        mCamera.stopPreview();
        mCamera.release();
        return true;
    }

    public void onSurfaceTextureUpdated(SurfaceTexture surface) {
        // Invoked every time there's a new Camera preview frame
        long time0 = System.currentTimeMillis();

        mTextureView.getBitmap(bmp);

        long time1 = System.currentTimeMillis() - time0;

        final Canvas c = mSurfaceHolder.lockCanvas();
        if ( c != null) {
            canvas.drawText("getBmp= "  + time1, 10, 40, paint1);
            c.drawBitmap(bmp, 0, 0, null);
            mSurfaceHolder.unlockCanvasAndPost(c);
        }
        long total = System.currentTimeMillis() - time0;
        long time2 = total -time1;
        Log.i("onFrame", "timing: getBmp= "  + time1 + " blit= " + time2 + " total= " + total);
    }
}

布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin" >

    <SurfaceView
        android:id="@+id/surfaceview"
        android:layout_width="640px"
        android:layout_height="480px" />

    <TextureView
        android:id="@+id/textureview"
        android:layout_width="640px"
        android:layout_height="480px" />

</LinearLayout>