android4.0 FaceDetection笔记

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) the

camera preview. Create a method for starting face detection so you can call it as needed, as shown

in 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();

    }

}

首先判断硬件是否支持该功能

 

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 {@link 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);

        }

而KEY_MAX_NUM_DETECTED_FACES_HW一般是在ＨＡＬ层initDefaultParameters函数里设置的，设置如下

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

initDefaultParameters里类似这样的代码，其它的我就不贴出来了.

 

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 {@link FaceDetectionListener} of the detected

     * faces in the preview frame. The detected faces may be the same as the

     * previous ones. Applications should call {@link #stopFaceDetection} to

     * stop the face detection. This method is supported if {@link

     * 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, {@link Parameters#setWhiteBalance(String)},

     * {@link Parameters#setFocusAreas(List)}, and {@link 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 {@link #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 {@link

     * #cancelAutoFocus()}, the face callbacks will also resume.</p>

     *

     * <p>After calling {@link #takePicture(Camera.ShutterCallback, Camera.PictureCallback,

     * Camera.PictureCallback)} or {@link #stopPreview()}, and then resuming

     * preview with {@link #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;

    }

_startFaceDetection在ＪＮＩ里,CAMERA_FACE_DETECTION_HW这里初始化值是0在这个文件的开始有定义

 

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 },

对应:android_hardware_Camera_startFaceDetection,内容如下:

 

 

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");

    }

}

这里camera->sendCommand对应

 

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;

}

到这里调用就结束了。

 

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.