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.