这一部分我们会全力讲透彻：
android 从获取摄像头的数据到显示到屏幕上中间所经过的业务逻辑和过程，并且我们还会单独的仿写一个demo来进行实现.
中间的过程中，我们会使用visio的UML类图来进行串讲。
我们主要分析的是java层的业务逻辑,请大家仔细看类之间的关系图.
CallActivity是我们的通话要显示的界面,摄像机的操作开始位置是在连接上房间服务器成功之后才开始的.
private void onConnectedToRoomInternal(final SignalingParameters params) {
final long delta = System.currentTimeMillis() - callStartedTimeMs;
signalingParameters = params;
logAndToast("Creating peer connection, delay=" + delta + "ms");
VideoCapturer videoCapturer = null;
if (peerConnectionParameters.videoCallEnabled) {
videoCapturer = createVideoCapturer();
}
peerConnectionClient.createPeerConnection(
localProxyVideoSink, remoteSinks, videoCapturer, signalingParameters);localProxyVideoSink，和 remoteSink只是VideoSink的代理者，代理的是最终的真正的数据消费者.
因为现在Camera启动有2种方式，所以CameraEnumerator对这种情况进行了封装，这里我们只针对第一种方式进行说明，也就是Camear1Capture来进行说明.
如果我们自己做渲染显示，那么就少不了几个步骤:
1.启动camera
2.camera的数据可以直接绑定一个纹理对象，然后通过 setOnFrameAvailable的方式来进行通知纹理更新
3.在纹理被通知更新，我们再通过opengl shader的方式来把数据显示到surface上.
webrtc的方式依然也是对这三种模式进行的封装.
SurfaceTextureHelper是一个handler线程，看下它的成员变量.
private final Handler handler;
private final EglBase eglBase;
private final SurfaceTexture surfaceTexture;
private final int oesTextureId;
private final YuvConverter yuvConverter = new YuvConverter();它内部维护一个handler线程，同时监控纹理的更新，如果纹理更新了，会把纹理数据封装为VideoFrame，然后通过进行回掉.
oesTextureId = GlUtil.generateTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES);
surfaceTexture = new SurfaceTexture(oesTextureId);
setOnFrameAvailableListener(surfaceTexture, (SurfaceTexture st) -> {
hasPendingTexture = true;
tryDeliverTextureFrame();
}, handler);通过listener把VideoFrame作为参数进行回掉,我们可以在外部进行
/**
* Start to stream textures to the given |listener|. If you need to change listener, you need to
* call stopListening() first.
*/
public void startListening(final VideoSink listener) {
startListeningInternal(listener);
}数据其实是回掉到了Camera1Session中了，我们可以在Camera1Session1的初始化的过程中，看到对应的代码:
private void listenForTextureFrames() {
//这里的VideoFrame是回调的时候生成的
surfaceTextureHelper.startListening((VideoFrame frame) -> {
checkIsOnCameraThread();
if (state != SessionState.RUNNING) {
Logging.d(TAG, "Texture frame captured but camera is no longer running.");
return;
}回掉的写法是lamba语法,
CameraSession主要是控制摄像头的open/close,startpreview操作的，然后通过回掉的方式再把事件传递回CameraCapture.
CameraSession中的2大事件回调接口.
// Callbacks are fired on the camera thread.
interface CreateSessionCallback {
void onDone(CameraSession session);
void onFailure(FailureType failureType, String error);
}
// Events are fired on the camera thread.
interface Events {
void onCameraOpening();
void onCameraError(CameraSession session, String error);
void onCameraDisconnected(CameraSession session);
void onCameraClosed(CameraSession session);
void onFrameCaptured(CameraSession session, VideoFrame frame);
}分别在CameraCapture中被实现.
private final CameraSession.CreateSessionCallback createSessionCallback =
new CameraSession.CreateSessionCallback() { private final CameraSession.Events cameraSessionEventsHandler = new CameraSession.Events() {
@Override
public void onCameraOpening() {所以最终的VideoFrame会被CameraCapture所捕获.
public void onFrameCaptured(CameraSession session, VideoFrame frame) {
checkIsOnCameraThread();
synchronized (stateLock) {
if (session != currentSession) {
Logging.w(TAG, "onFrameCaptured from another session.");
return;
}
if (!firstFrameObserved) {
eventsHandler.onFirstFrameAvailable();
firstFrameObserved = true;
}
cameraStatistics.addFrame();
capturerObserver.onFrameCaptured(frame);
}
}
};
这个capturerObserver其实是NativeCapturerObserver,NativeCapturerObserver是CameraCapture的成员.
NativeCapturerObserver则直接把数据给丢到了ndk层去处理。
public void onFrameCaptured(VideoFrame frame) {
int width = frame.getBuffer().getWidth();
int height = frame.getBuffer().getHeight();
int rotation = frame.getRotation();
long timeNs = frame.getTimestampNs();
VideoFrame.Buffer buffer = frame.getBuffer() ;
nativeOnFrameCaptured(nativeSource, width , height , rotation, timeNs , buffer);
}ndk对数据进行处理后，会调用上层的VideoSink的onFrame.
流程就是按照上面的方式进行处理的.
所以我们很容易知道SurfaceViewRender被传递到了ndk层，给了VideoBroadCast，VideoBroadCast以广播的方式通知所有的sinks，去处理VideoFrame,而SurfaceViewRender就是调用了onFrame来进行处理.
SurfaceViewRender本身继承于SurfaceView,跟踪代码就会发现最终会嗲用opengl 模块.
最终GLRectDrawer把外置纹理绘制到了Surface上.
public void drawOes(int oesTextureId, float[] texMatrix, int frameWidth, int frameHeight,
int viewportX, int viewportY, int viewportWidth, int viewportHeight) {
prepareShader(
ShaderType.OES, texMatrix, frameWidth, frameHeight, viewportWidth, viewportHeight);
// Bind the texture.
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, oesTextureId);
// Draw the texture.
GLES20.glViewport(viewportX, viewportY, viewportWidth, viewportHeight);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
// Unbind the texture as a precaution.
GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, 0);
}总结 ：
这里只是大概的帮大家理清下类之间的关系依赖，类似大厦的设计图纸，后面我们就要分析细节。
要想明白，作者为什么要这么设计，是基于什么目的呢？