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:

[java] view plain copy print ?

1. /*Your application must start the face detection function each time you start (or restart) the 
2. camera preview. Create a method for starting face detection so you can call it as needed, as shown 
3. in the example code below.*/  
4.   
5. public void startFaceDetection(){  
6.     // Try starting Face Detection   
7.     ....  
8.     // start face detection only *after* preview has started   
9.     if (params.getMaxNumDetectedFaces() > 0){  
10.         // camera supports face detection, so can start it:   
11.         mCamera.startFaceDetection();  
12.     }  
13. }  

/*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:

[java] view plain copy print ?

1. /** 
2.  * Gets the maximum number of detected faces supported. This is the 
3.  * maximum length of the list returned from {@link FaceDetectionListener}. 
4.  * If the return value is 0, face detection of the specified type is not 
5.  * supported. 
6.  * 
7.  * @return the maximum number of detected face supported by the camera. 
8.  * @see #startFaceDetection() 
9.  */  
10. public int getMaxNumDetectedFaces() {  
11.     return getInt(KEY_MAX_NUM_DETECTED_FACES_HW, 0);  
12. }  

        /**
         * 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

[java] view plain copy print ?

1. <SPAN style="FONT-SIZE: 12px">p.set(CameraParameters::KEY_MAX_NUM_DETECTED_FACES_HW, "1"); //add by dao set the max face detectctor number </SPAN>  

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:

[java] view plain copy print ?

1. /** 
2.  * Starts the face detection. This should be called after preview is started. 
3.  * The camera will notify {@link FaceDetectionListener} of the detected 
4.  * faces in the preview frame. The detected faces may be the same as the 
5.  * previous ones. Applications should call {@link #stopFaceDetection} to 
6.  * stop the face detection. This method is supported if {@link 
7.  * Parameters#getMaxNumDetectedFaces()} returns a number larger than 0. 
8.  * If the face detection has started, apps should not call this again. 
9.  * 
10.  * <p>When the face detection is running, {@link Parameters#setWhiteBalance(String)}, 
11.  * {@link Parameters#setFocusAreas(List)}, and {@link Parameters#setMeteringAreas(List)} 
12.  * have no effect. The camera uses the detected faces to do auto-white balance, 
13.  * auto exposure, and autofocus. 
14.  * 
15.  * <p>If the apps call {@link #autoFocus(AutoFocusCallback)}, the camera 
16.  * will stop sending face callbacks. The last face callback indicates the 
17.  * areas used to do autofocus. After focus completes, face detection will 
18.  * resume sending face callbacks. If the apps call {@link 
19.  * #cancelAutoFocus()}, the face callbacks will also resume.</p> 
20.  * 
21.  * <p>After calling {@link #takePicture(Camera.ShutterCallback, Camera.PictureCallback, 
22.  * Camera.PictureCallback)} or {@link #stopPreview()}, and then resuming 
23.  * preview with {@link #startPreview()}, the apps should call this method 
24.  * again to resume face detection.</p> 
25.  * 
26.  * @throws IllegalArgumentException if the face detection is unsupported. 
27.  * @throws RuntimeException if the method fails or the face detection is 
28.  *         already running. 
29.  * @see FaceDetectionListener 
30.  * @see #stopFaceDetection() 
31.  * @see Parameters#getMaxNumDetectedFaces() 
32.  */  
33. public final void startFaceDetection() {  
34.     if (mFaceDetectionRunning) {  
35.         throw new RuntimeException("Face detection is already running");  
36.     }  
37.     _startFaceDetection(CAMERA_FACE_DETECTION_HW);  
38.     mFaceDetectionRunning = true;  
39. }  

    /**
     * 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:

[java] view plain copy print ?

1. { "_startFaceDetection",  
2.   "(I)V",  
3.   (void *)android_hardware_Camera_startFaceDetection },  

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

对应:android_hardware_Camera_startFaceDetection,内容如下:

[java] view plain copy print ?

1. static void android_hardware_Camera_startFaceDetection(JNIEnv *env, jobject thiz,  
2.         jint type)  
3. {  
4.     LOGV("startFaceDetection");  
5.     JNICameraContext* context;  
6.     sp<Camera> camera = get_native_camera(env, thiz, &context);  
7.     if (camera == 0) return;  
8.   
9.     status_t rc = camera->sendCommand(CAMERA_CMD_START_FACE_DETECTION, type, 0);  
10.     if (rc == BAD_VALUE) {  
11.         char msg[64];  
12.         snprintf(msg, sizeof(msg), "invalid face detection type=%d", type);  
13.         jniThrowException(env, "java/lang/IllegalArgumentException", msg);  
14.     } else if (rc != NO_ERROR) {  
15.         jniThrowRuntimeException(env, "start face detection failed");  
16.     }  
17. }  

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

[java] view plain copy print ?

1. status_t CameraHardwareSec::sendCommand(int32_t command, int32_t arg1, int32_t arg2)  
2. {  
3.     return BAD_VALUE;  
4. }  

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.
资料参考:http://blog.youkuaiyun.com/qq69696698/article/details/7325772