Android(安卓)camera HAL四个callback

CameraHardwareInterface.h定义了CameraService和CameraHAL之间的接口，在这个文件中定义了四个回调函数

typedef camera_memory_t* (*camera_request_memory)(int fd, size_t buf_size, unsigned int num_bufs,                                                  void *user);typedef void (*camera_notify_callback)(int32_t msg_type,        int32_t ext1,        int32_t ext2,        void *user);typedef void (*camera_data_callback)(int32_t msg_type,        const camera_memory_t *data, unsigned int index,        camera_frame_metadata_t *metadata, void *user);typedef void (*camera_data_timestamp_callback)(int64_t timestamp,        int32_t msg_type,        const camera_memory_t *data, unsigned int index,        void *user);

这四个回调函数在frameworks/av/services/camera/libcameraservice/CameraClient.cpp中实现。

camera_request_memory

Camera HAL通知CameraService申请buffer

@buf_size: buf的大小

@num_bufs：buf数目

msg_type的取值范围定义在 android/system/core/include/system/camera.h中

/** msgType in notifyCallback and dataCallback functions */enum {    CAMERA_MSG_ERROR = 0x0001,            // notifyCallback    CAMERA_MSG_SHUTTER = 0x0002,          // notifyCallback    CAMERA_MSG_FOCUS = 0x0004,            // notifyCallback    CAMERA_MSG_ZOOM = 0x0008,             // notifyCallback    CAMERA_MSG_PREVIEW_FRAME = 0x0010,    // dataCallback    CAMERA_MSG_VIDEO_FRAME = 0x0020,      // data_timestamp_callback    CAMERA_MSG_POSTVIEW_FRAME = 0x0040,   // dataCallback    CAMERA_MSG_RAW_IMAGE = 0x0080,        // dataCallback    CAMERA_MSG_COMPRESSED_IMAGE = 0x0100, // dataCallback    CAMERA_MSG_RAW_IMAGE_NOTIFY = 0x0200, // dataCallback    // Preview frame metadata. This can be combined with    // CAMERA_MSG_PREVIEW_FRAME in dataCallback. For example, the apps can    // request FRAME and METADATA. Or the apps can request only FRAME or only    // METADATA.    CAMERA_MSG_PREVIEW_METADATA = 0x0400, // dataCallback    // Notify on autofocus start and stop. This is useful in continuous    // autofocus - FOCUS_MODE_CONTINUOUS_VIDEO and FOCUS_MODE_CONTINUOUS_PICTURE.    CAMERA_MSG_FOCUS_MOVE = 0x0800,       // notifyCallback    CAMERA_MSG_ALL_MSGS = 0xFFFF};

camera_notify_callback

用来传递一些消息: 如快门消息，自动对焦完成消息，出错消息，拍照编码结束等

参数@msg_type可以是：

CAMERA_MSG_ERROR
CAMERA_MSG_SHUTTER
CAMERA_MSG_FOCUS
CAMERA_MSG_ZOOM
CAMERA_MSG_FOCUS_MOVE

camera_data_callback

该函数用于从camera HAL返回数据，

返回的数据可以是：

preview的数据帧，
preview的元数据，
以及压缩为jpeg格式的帧数据

参数@msg_type可以是：

CAMERA_MSG_PREVIEW_FRAME
CAMERA_MSG_PREVIEW_METADATA
CAMERA_MSG_COMPRESSED_IMAGE
CAMERA_MSG_RAW_IMAGE
CAMERA_MSG_RAW_IMAGE_NOTIFY
CAMERA_MSG_POSTVIEW_FRAME

参数@data 用来返回图像数据

参数@metadata 用来返回图像的元数据

camera_data_timestamp_callback

该回调函数用来从Camera HAL返回帧数据以及对应的时间戳，这个callback用于录像的场景。

@timestamp：生成帧数据的时间戳

@msg_type: 取值为CAMERA_MSG_VIDEO_FRAME

@data：用来返回帧数据

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