android4.0 FaceDetection札记

这几天研究了下andoid4.0.3的FaceDetection这里写一下大致的流程，方便日后查阅。

相关说明可以在这里找到:

frameworks/base/docs/html/guide/topics/media/camera.jd

起始代码可以在camera.jd里找到也可以在

packages/apps/Camera/src/com/android/camera/Camera.java里找到，具体代码我就不说了.

一般起始点是startFaceDetection函数

startFaceDetection函数大致内容如下:

/*Your application must start the face detection function each time you start (or restart) thecamera preview. Create a method for starting face detection so you can call it as needed, as shownin the example code below.*/public void startFaceDetection(){    // Try starting Face Detection    ....    // start face detection only *after* preview has started    if (params.getMaxNumDetectedFaces() > 0){        // camera supports face detection, so can start it:        mCamera.startFaceDetection();    }}

getMaxNumDetectedFaces函数在

frameworks/base/core/java/android/hardware/Camera.java

内容如下:

        /**         * Gets the maximum number of detected faces supported. This is the         * maximum length of the list returned from [email protected] FaceDetectionListener}.         * If the return value is 0, face detection of the specified type is not         * supported.         *         * @return the maximum number of detected face supported by the camera.         * @see #startFaceDetection()         */        public int getMaxNumDetectedFaces() {            return getInt(KEY_MAX_NUM_DETECTED_FACES_HW, 0);        }

p.set(CameraParameters::KEY_MAX_NUM_DETECTED_FACES_HW, "1"); //add by dao set the max face detectctor number 

mCamera.startFaceDetection();这个是执行的

frameworks/base/core/java/android/hardware/Camera.java里的startFaceDetection函数,内容如下:

    /**     * Starts the face detection. This should be called after preview is started.     * The camera will notify [email protected] FaceDetectionListener} of the detected     * faces in the preview frame. The detected faces may be the same as the     * previous ones. Applications should call [email protected] #stopFaceDetection} to     * stop the face detection. This method is supported if [email protected]     * Parameters#getMaxNumDetectedFaces()} returns a number larger than 0.     * If the face detection has started, apps should not call this again.     *     * <p>When the face detection is running, [email protected] Parameters#setWhiteBalance(String)},     * [email protected] Parameters#setFocusAreas(List)}, and [email protected] Parameters#setMeteringAreas(List)}     * have no effect. The camera uses the detected faces to do auto-white balance,     * auto exposure, and autofocus.     *     * <p>If the apps call [email protected] #autoFocus(AutoFocusCallback)}, the camera     * will stop sending face callbacks. The last face callback indicates the     * areas used to do autofocus. After focus completes, face detection will     * resume sending face callbacks. If the apps call [email protected]     * #cancelAutoFocus()}, the face callbacks will also resume.</p>     *     * <p>After calling [email protected] #takePicture(Camera.ShutterCallback, Camera.PictureCallback,     * Camera.PictureCallback)} or [email protected] #stopPreview()}, and then resuming     * preview with [email protected] #startPreview()}, the apps should call this method     * again to resume face detection.</p>     *     * @throws IllegalArgumentException if the face detection is unsupported.     * @throws RuntimeException if the method fails or the face detection is     *         already running.     * @see FaceDetectionListener     * @see #stopFaceDetection()     * @see Parameters#getMaxNumDetectedFaces()     */    public final void startFaceDetection() {        if (mFaceDetectionRunning) {            throw new RuntimeException("Face detection is already running");        }        _startFaceDetection(CAMERA_FACE_DETECTION_HW);        mFaceDetectionRunning = true;    }

在frameworks/base/core/jni/android_hardware_Camera.cpp我们可以找到_startFaceDetection对应的函数:

  { "_startFaceDetection",    "(I)V",    (void *)android_hardware_Camera_startFaceDetection },

static void android_hardware_Camera_startFaceDetection(JNIEnv *env, jobject thiz,        jint type){    LOGV("startFaceDetection");    JNICameraContext* context;    sp<Camera> camera = get_native_camera(env, thiz, &context);    if (camera == 0) return;    status_t rc = camera->sendCommand(CAMERA_CMD_START_FACE_DETECTION, type, 0);    if (rc == BAD_VALUE) {        char msg[64];        snprintf(msg, sizeof(msg), "invalid face detection type=%d", type);        jniThrowException(env, "java/lang/IllegalArgumentException", msg);    } else if (rc != NO_ERROR) {        jniThrowRuntimeException(env, "start face detection failed");    }}

device/samsung/common/s5p/libcamera/SecCameraHWInterface.cpp文件里的sendCommand函数,内容如下

status_t CameraHardwareSec::sendCommand(int32_t command, int32_t arg1, int32_t arg2){    return BAD_VALUE;}

不同的产家camera的库所存放的目录可能不一样,同时这个函数需要根据具体的要求，进行修改.
资料参考:http://blog.csdn.net/qq69696698/article/details/7325772