Android 5.0(Lollipop)中的SurfaceTexture，TextureView, SurfaceView和GLSurfaceView

SurfaceView从Android 1.0(API level 1)时就有 。它继承自类View，因此它本质上是一个View。但与普通View不同的是，它有自己的Surface。我们知道，一般的Activity包含的多个View会组成View hierachy的树形结构，只有最顶层的DecorView，也就是根结点视图，才是对WMS可见的。这个DecorView在WMS中有一个对应的WindowState。相应地，在SF中对应的Layer。而SurfaceView自带一个Surface，这个Surface在WMS中有自己对应的WindowState，在SF中也会有自己的Layer。如下图所示：

public class TriangleActivity extends Activity {
    protected void onCreate(Bundle savedInstanceState) {
        mGLView = new GLSurfaceView(this);
        mGLView.setRenderer(new RendererImpl(this));

SurfaceTexture从Android 3.0(API level 11)加入。和SurfaceView不同的是，它对图像流的处理并不直接显示，而是转为GL外部纹理，因此可用于图像流数据的二次处理（如Camera滤镜，桌面特效等）。比如Camera的预览数据，变成纹理后可以交给GLSurfaceView直接显示，也可以通过SurfaceTexture交给TextureView作为View heirachy中的一个硬件加速层来显示。首先，SurfaceTexture从图像流（来自Camera预览，视频解码，GL绘制场景等）中获得帧数据，当调用updateTexImage()时，根据内容流中最近的图像更新SurfaceTexture对应的GL纹理对象，接下来，就可以像操作普通GL纹理一样操作它了。从下面的类图中可以看出，它核心管理着一个BufferQueue的Consumer和Producer两端。Producer端用于内容流的源输出数据，Consumer端用于拿GraphicBuffer并生成纹理。SurfaceTexture.OnFrameAvailableListener用于让SurfaceTexture的使用者知道有新数据到来。JNISurfaceTextureContext是OnFrameAvailableListener从Native到Java的JNI跳板。其中SurfaceTexture中的attachToGLContext()和detachToGLContext()可以让多个GL context共享同一个内容源。

TextureView在4.0(API level 14)中引入。它可以将内容流直接投影到View中，可以用于实现Live preview等功能。和SurfaceView不同，它不会在WMS中单独创建窗口，而是作为View hierachy中的一个普通View，因此可以和其它普通View一样进行移动，旋转，缩放，动画等变化。值得注意的是TextureView必须在硬件加速的窗口中。它显示的内容流数据可以来自App进程或是远端进程。从类图中可以看到，TextureView继承自View，它与其它的View一样在View hierachy中管理与绘制。TextureView重载了draw()方法，其中主要把SurfaceTexture中收到的图像数据作为纹理更新到对应的HardwareLayer中。SurfaceTexture.OnFrameAvailableListener用于通知TextureView内容流有新图像到来。SurfaceTextureListener接口用于让TextureView的使用者知道SurfaceTexture已准备好，这样就可以把SurfaceTexture交给相应的内容源。Surface为BufferQueue的Producer接口实现类，使生产者可以通过它的软件或硬件渲染接口为SurfaceTexture内部的BufferQueue提供graphic buffer。

109    public VideoDumpView(Context context) {
...
116        mRenderer = new VideoDumpRenderer(context);
117        setRenderer(mRenderer);
118    }

519        public void onSurfaceCreated(GL10 glUnused, EGLConfig config) {
...
551            // Create our texture. This has to be done each time the surface is created.
552            int[] textures = new int[1];
553            GLES20.glGenTextures(1, textures, 0);
554
555            mTextureID = textures[0];
556            GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, mTextureID);
...
575            mSurface = new SurfaceTexture(mTextureID);
576            mSurface.setOnFrameAvailableListener(this);
577
578            Surface surface = new Surface(mSurface);
579            mMediaPlayer.setSurface(surface);

230static void SurfaceTexture_init(JNIEnv* env, jobject thiz, jboolean isDetached,
231        jint texName, jboolean singleBufferMode, jobject weakThiz)
232{
...
235    BufferQueue::createBufferQueue(&producer, &consumer);
...
242    sp<GLConsumer> surfaceTexture;
243    if (isDetached) {
244        surfaceTexture = new GLConsumer(consumer, GL_TEXTURE_EXTERNAL_OES,
245                true, true);
246    } else {
247        surfaceTexture = new GLConsumer(consumer, texName,
248                GL_TEXTURE_EXTERNAL_OES, true, true);
249    }
...
256    SurfaceTexture_setSurfaceTexture(env, thiz, surfaceTexture);
257    SurfaceTexture_setProducer(env, thiz, producer);
...
266    sp<JNISurfaceTextureContext> ctx(new JNISurfaceTextureContext(env, weakThiz,
267            clazz));
268    surfaceTexture->setFrameAvailableListener(ctx);
269    SurfaceTexture_setFrameAvailableListener(env, thiz, ctx);

180void JNISurfaceTextureContext::onFrameAvailable()
...
184        env->CallStaticVoidMethod(mClazz, fields.postEvent, mWeakThiz);

133    public Surface(SurfaceTexture surfaceTexture) {
...
140            setNativeObjectLocked(nativeCreateFromSurfaceTexture(surfaceTexture));

135static jlong nativeCreateFromSurfaceTexture(JNIEnv* env, jclass clazz,
136        jobject surfaceTextureObj) {
137    sp<IGraphicBufferProducer> producer(SurfaceTexture_getProducer(env, surfaceTextureObj));
...
144    sp<Surface> surface(new Surface(producer, true));

372        public void onDrawFrame(GL10 glUnused) {
...
377                if (updateSurface) {
...
380                    mSurface.updateTexImage();
381                    mSurface.getTransformMatrix(mSTMatrix);
382                    updateSurface = false;
...
394            // Activate the texture.
395            GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
396            GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, mTextureID);
...
421            // Draw a rectangle and render the video frame as a texture on it.
422            GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
...
429                DumpToFile(frameNumber);

      protected void onCreate(Bundle savedInstanceState) {
          ...
          mTextureView = new TextureView(this);
          mTextureView.setSurfaceTextureListener(this);
          ...
      }

348    HardwareLayer getHardwareLayer() {
...
358            mLayer = mAttachInfo.mHardwareRenderer.createTextureLayer();
359            if (!mUpdateSurface) {
360                // Create a new SurfaceTexture for the layer.
361                mSurface = new SurfaceTexture(false);
362                mLayer.setSurfaceTexture(mSurface);
363            }
364            mSurface.setDefaultBufferSize(getWidth(), getHeight());
365            nCreateNativeWindow(mSurface);
366
367            mSurface.setOnFrameAvailableListener(mUpdateListener, mAttachInfo.mHandler);
368
369            if (mListener != null && !mUpdateSurface) {
370                mListener.onSurfaceTextureAvailable(mSurface, getWidth(), getHeight());
371            }
...
390        applyUpdate();
391        applyTransformMatrix();
392
393        return mLayer;
394    }

      public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
          mCamera = Camera.open();
              ...
              mCamera.setPreviewTexture(surface);
              mCamera.startPreview();
              ...
      }

576static void android_hardware_Camera_setPreviewTexture(JNIEnv *env,
577        jobject thiz, jobject jSurfaceTexture)
...
585        producer = SurfaceTexture_getProducer(env, jSurfaceTexture);
...
594    if (camera->setPreviewTarget(producer) != NO_ERROR) {

755        public void onFrameAvailable(SurfaceTexture surfaceTexture) {
756            updateLayer();
757            invalidate();
758        }

138    public void updateSurfaceTexture() {
139        nUpdateSurfaceTexture(mFinalizer.get());
140        mRenderer.pushLayerUpdate(this);
141    }