Android Camera数据流完整分析

之前已经有很多文章一直在讲述Android Camera，这里也算是进行以下总结

我们依旧从camera 的打开开始，逐步看看camera的数据流向，内存分配，首先打开camera的第一步，实例化camera类，onCreate被调用，在这个方法中到底做了些什么事情，也在这里做一下总结:

1.实例化FocusManager

2.开启一个CameraOpenThread用于打开camera的全部过程，mCameraOpenThread.start();

3.实例化PreferenceInflater，初始化一些参数

4.实例化TouchManager

5.实例化RotateDialogController等等等

重点是下面几行代码，之前已经不止一次提到，不在多说了

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// don't set mSu易做图ceHolder here. We have it set ONLY within
// su易做图ceChanged / su易做图ceDestroyed, other parts of the code
// assume that when it is set, the su易做图ce is also set.
Su易做图ceView preview = (Su易做图ceView) findViewById(R.id.camera_preview);
Su易做图ceHolder holder = preview.getHolder();
holder.addCallback(this);

        // don't set mSu易做图ceHolder here. We have it set ONLY within
        // su易做图ceChanged / su易做图ceDestroyed, other parts of the code
        // assume that when it is set, the su易做图ce is also set.
        Su易做图ceView preview = (Su易做图ceView) findViewById(R.id.camera_preview);
        Su易做图ceHolder holder = preview.getHolder();
        holder.addCallback(this);另外这个方法中，还开启了一个startPreviewThread用于开始preview过程，初始化完成之后就开启preview功能

[html]
Thread mCameraPreviewThread = new Thread(new Runnable() {
    public void run() {
        initializeCapabilities();
        startPreview(true);
    }
});

    Thread mCameraPreviewThread = new Thread(new Runnable() {
        public void run() {
            initializeCapabilities();
            startPreview(true);
        }
    });这个线程进行初始化之后就调用了app层的startPreview方法，这里开始了万里长征的第一步

这里还是花一点时间说说camera的打开过程，从app调用到的open方法过程这之前的文章中已经讲过，在底层的open方法中完成以下工作

1.为上层调用注册调用接口

2.实例化hal层，并初始化，这个hal层初始化的过程同样之前的文章中已经详细讲过，这个初始化过程非常重要，直接影响着之后的操作

回到我们的startPreview，一步一步看看他的走向

app层---------------------------做一些基本初始化，最重要的就是setPreviewwindow这个方法了，之前也已经详细分析过了，然后调用frameworks层的方法

frameworks层 ---------------这里只是定义了startPreview这个方式，通过JNI层调用

JNI层---------------------------这里作为一个中间站，不做任何处理，转去调用下一层实现

camera client层-------------同样可以理解为一个中转站，通过binder机制接着往下走

camera server层------------初始化显示窗口属性，调用下一层

hardware inte易做图ce层------转调camerahal_module中的方法

camera hal层----------------这个hal层的startPreview实现是整个preview过程中最为重要的部分，下面再说明

下面就是通过hal层分发命令通过V4LCameraAdapter或者OMXCameraAdapter与kernel driver进行交互

我们看一下server层的调用，相对较重要

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status_t CameraService::Client::startPreview() {
LOG1("startPreview (pid %d)", getCallingPid());
return startCameraMode(<SPAN style="BACKGROUND-COLOR: rgb(51,255,51)">CAMERA_PREVIEW_MODE</SPAN>);
}

status_t CameraService::Client::startPreview() {
    LOG1("startPreview (pid %d)", getCallingPid());
    return startCameraMode(CAMERA_PREVIEW_MODE);
}[html] view plaincopyprint?// start preview or recording
status_t CameraService::Client::startCameraMode(camera_mode mode) {
    LOG1("startCameraMode(%d)", mode);
    Mutex::Autolock lock(mLock);
    status_t result = checkPidAndHardware();
    if (result != NO_ERROR) return result;

    switch(mode) {
        case CAMERA_PREVIEW_MODE:
            if (mSu易做图ce == 0 && mPreviewWindow == 0) {
                LOG1("mSu易做图ce is not set yet.");
                // still able to start preview in this case.
            }
            <SPAN style="BACKGROUND-COLOR: rgb(51,255,51)">return startPreviewMode();</SPAN>
        case CAMERA_RECORDING_MODE:
            if (mSu易做图ce == 0 && mPreviewWindow == 0) {
                LOGE("mSu易做图ce or mPreviewWindow must be set before startRecordingMode.");
                return INVALID_OPERATION;
            }
            return startRecordingMode();
        default:
            return UNKNOWN_ERROR;
    }
}

// start preview or recording
status_t CameraService::Client::startCameraMode(camera_mode mode) {
    LOG1("startCameraMode(%d)", mode);
    Mutex::Autolock lock(mLock);
    status_t result = checkPidAndHardware();
    if (result != NO_ERROR) return result;

    switch(mode) {
        case CAMERA_PREVIEW_MODE:
            if (mSu易做图ce == 0 && mPreviewWindow == 0) {
                LOG1("mSu易做图ce is not set yet.");
                // still able to start preview in this case.
            }
            return startPreviewMode();
        case CAMERA_RECORDING_MODE:
            if (mSu易做图ce == 0 && mPreviewWindow == 0) {
                LOGE("mSu易做图ce or mPreviewWindow must be set before startRecordingMode.");
                return INVALID_OPERATIO

补充：移动开发 , Android ,