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文章將會(huì)同步到個(gè)人微信公眾號(hào)：Android部落格

1富岳、項(xiàng)目需求

項(xiàng)目整體的需求是Android盒子支持上下左右控制云臺(tái)攝像頭抢韭，還要能相對(duì)和絕對(duì)控制攝像頭的位置。相對(duì)控制堕仔，意思就是按著左方向鍵不放英融，攝像頭一直往左邊轉(zhuǎn)趴俘，到最大值為止，反之亦然掌眠；絕對(duì)控制蕾盯，意思是每次按一下方向鍵，就轉(zhuǎn)一個(gè)角度就停下來蓝丙。

2级遭、需求實(shí)現(xiàn)

最終選擇通過定制Android kernel層的uvc代碼望拖，編譯kernel，打包固件挫鸽，刷機(jī)说敏，編寫上層App，從上到下打通控制流程丢郊。

3盔沫、靈感來源

驗(yàn)證Android盒子是否支持控制云臺(tái)攝像頭，只需要將攝像頭連接到ubuntu虛擬機(jī)枫匾，通過ubuntu上面的工具即可以控制攝像頭旋轉(zhuǎn)架诞，也就可以通過改造Android的kernel支持對(duì)應(yīng)的功能。

之前的文章里面有提到過干茉，使用uvcdynctrl工具谴忧，輸入對(duì)應(yīng)的指令就行，這里看看他的源碼是怎么實(shí)現(xiàn)的：

https://github.com/llmike/v4l2-tools/blob/master/libwebcam-src-0.2.4/libwebcam/libwebcam.c

struct v4l2_control v4l2_ctrl = {
    .id     = control->v4l2_control,
    .value  = value->value
};
if(ioctl(v4l2_dev, VIDIOC_S_CTRL, &v4l2_ctrl)) {
    ret = C_V4L2_ERROR;
    set_last_error(hDevice, errno);
}

struct v4l2_control v4l2_ctrl = { .id = control->v4l2_control };
if(ioctl(v4l2_dev, VIDIOC_G_CTRL, &v4l2_ctrl)) {
    ret = C_V4L2_ERROR;
    set_last_error(hDevice, errno);
    goto done;
}
value->value    = v4l2_ctrl.value;

VIDIOC_S_CTRL和VIDIOC_G_CTRL的解釋詳見如下鏈接角虫，一個(gè)用于設(shè)置參數(shù)沾谓，一個(gè)用于獲取參數(shù)。

https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html#vidioc-g-ctrl

v4l2_control是兩個(gè)操作中間的媒介上遥，新的數(shù)據(jù)可以通過VIDIOC_S_CTRL傳遞這個(gè)結(jié)構(gòu)體搏屑；當(dāng)設(shè)置id之后，通過VIDIOC_G_CTRL粉楚，可以返回需要的數(shù)據(jù)辣恋。

這個(gè)id填什么參數(shù)呢？是struct uvc_control_mapping uvc_ctrl_mappings中對(duì)應(yīng)的id模软，這個(gè)id就是具體攝像頭支持的參數(shù)id伟骨，在設(shè)置之前先要查詢攝像頭支持的參數(shù)，只有它支持之后才能設(shè)置燃异。

3.1 上層JNI代碼編寫

獲取攝像頭支持的控制參數(shù)：

jboolean queryControls(){
    jint canControl = 0;
    __android_log_print(ANDROID_LOG_ERROR , TAG , "設(shè)備號(hào)=%d" , fd);

    struct v4l2_queryctrl qctrl;
    qctrl.id = V4L2_CTRL_CLASS_CAMERA | V4L2_CTRL_FLAG_NEXT_CTRL;
    int i = ioctl(fd, VIDIOC_QUERYCTRL, &qctrl);
    while (0 == i){
        __android_log_print(ANDROID_LOG_ERROR , TAG , "開始查找");
        if (V4L2_CTRL_ID2CLASS(qctrl.id) != V4L2_CTRL_CLASS_CAMERA)
            continue;

        if(strcmp(qctrl.name , CONTROL_FLAG_PAN) == 0 || strcmp(qctrl.name , CONTROL_FLAG_TILT) == 0
                            || strcmp(qctrl.name , CONTROL_FLAG_ZOOM) == 0){
            ++canControl;
        }

        __android_log_print(ANDROID_LOG_ERROR , TAG , "找到的控制函數(shù)是%s" , qctrl.name);
        __android_log_print(ANDROID_LOG_ERROR , TAG , "繼續(xù)查找");
        __android_log_print(ANDROID_LOG_ERROR , TAG , "id = %d" , qctrl.id);
        __android_log_print(ANDROID_LOG_ERROR , TAG , "Next_Ctrl = %x" , V4L2_CTRL_FLAG_NEXT_CTRL);
        __android_log_print(ANDROID_LOG_ERROR , TAG , "Camera_Class = %x" , V4L2_CTRL_CLASS_CAMERA);

        qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;

        __android_log_print(ANDROID_LOG_ERROR , TAG , "id+ = %x" , qctrl.id);

        i = ioctl(fd, VIDIOC_QUERYCTRL, &qctrl);
        if(i != 0){
            __android_log_print(ANDROID_LOG_ERROR, TAG,"uvcioc ctrl add error: errno=%d (reason=%s)\n", errno,strerror(errno));
        }
    }
    //如果存在ptz控制的話携狭，應(yīng)該會(huì)有Pan,Tilt,Zoom字符串，變量自加三次
    return canControl == 3;
}

獲取某個(gè)id當(dāng)前對(duì)應(yīng)的值：

int getControlValue(int controlId){
    //an array of v4l2_ext_control
    struct v4l2_ext_control clist[1];
    struct v4l2_ext_controls ctrls;

    memset(&clist, 0, sizeof(clist));
    memset(&ctrls, 0, sizeof(ctrls));

    clist[0].id    = controlId;
    clist[0].value = 0;

    //v4l2_ext_controls with list of v4l2_ext_control
    ctrls.ctrl_class = V4L2_CTRL_CLASS_CAMERA;
    ctrls.count = 1;
    ctrls.controls = clist;

    //read back the value
    if (-1 == xioctl (fd, VIDIOC_G_EXT_CTRLS, &ctrls))
    {
        __android_log_print(ANDROID_LOG_ERROR,TAG,"get current value failed fd = %d,reason=%s" , fd,strerror(errno));
        return -1;
    }
    __android_log_print(ANDROID_LOG_ERROR,TAG,"get before value success , %d" , clist[0].value);
    return clist[0].value;
}

設(shè)置某個(gè)參數(shù)的值回俐，也就是開始控制攝像頭左右上下轉(zhuǎn)動(dòng)了：

int startControl(int controlId , int value){
    //an array of v4l2_ext_control
    struct v4l2_ext_control clist[1];
    struct v4l2_ext_controls ctrls;
    CLEAR(clist);
    CLEAR(ctrls);
    
    clist[0].id    = controlId;
    clist[0].value = value;
    
    //v4l2_ext_controls with list of v4l2_ext_control
    ctrls.ctrl_class = V4L2_CTRL_CLASS_CAMERA;
    ctrls.count = 1;
    ctrls.controls = clist;
    
    int result = xioctl(fd, VIDIOC_S_EXT_CTRLS, &ctrls);
}

v4l2_ext_control對(duì)應(yīng)的value值應(yīng)該按照協(xié)議文檔中對(duì)值的定義來傳逛腿，比如左右絕對(duì)控制的值對(duì)應(yīng)的是轉(zhuǎn)動(dòng)的角度；左右相對(duì)控制分為四位仅颇，每一個(gè)位表示不同的控制方式单默，需要按照不同的id傳遞不同的值。

v4l2_ext_controls可以在一個(gè)id下同時(shí)要控制多個(gè)參數(shù)忘瓦，具體詳見：
https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html#v4l2-ext-control搁廓。

4、底層定制

上邊的代碼寫好了之后，可以先選取某個(gè)非控制左右上下轉(zhuǎn)動(dòng)的id試一下境蜕，看看能否正確控制蝙场，然后再去調(diào)試pan，tilt功能粱年。

一般情況下要和攝像頭廠商配合聯(lián)調(diào)售滤，因?yàn)閿z像頭廠商的固件也要適配UVC協(xié)議。其中UVC協(xié)議版本是個(gè)大問題逼泣，在Android kernel中查看UVC版本的地方在：

goldfish\drivers\media\usb\uvc\uvcvideo.h

#define DRIVER_VERSION      "1.1.1"

如果kernel中UVC版本與攝像頭固件UVC版本不一致趴泌，會(huì)導(dǎo)致控制位不匹配，導(dǎo)致控制返回失敗拉庶。

到這里可以知道攝像頭的固件版本嗜憔，支持的控制參數(shù)，從而可以知道盒子Android底層kernel的定制方向了氏仗。當(dāng)前項(xiàng)目的定制方向是添加pan和tilt的相對(duì)控制能力吉捶。定制流程如下：

goldfish\include\uapi\linux\v4l2-controls.h

在這個(gè)文件中相對(duì)控制的速度：

#define V4L2_CID_PAN_SPEED (V4L2_CID_CAMERA_CLASS_BASE+32)
#define V4L2_CID_TILT_SPEED (V4L2_CID_CAMERA_CLASS_BASE+33)

goldfish\drivers\media\v4l2-core\v4l2-ctrls.c

文件中添加相對(duì)控制速度的描述：

const char *v4l2_ctrl_get_name(u32 id)
{
    case V4L2_CID_PAN_SPEED: return "Pan, Speed";
    case V4L2_CID_TILT_SPEED: return "Tilt, Speed";
}

goldfish\drivers\media\usb\uvc\uvc_ctrl.c

這個(gè)文件是核心的控制文件，里面包含了設(shè)置和獲取的方法皆尔，最終都到這個(gè)文件中實(shí)現(xiàn)呐舔，在這里我們需要添加相對(duì)控制的方法：

#define UVC_CTRL_RELATIVE_PAN 10094852
#define UVC_CTRL_RELATIVE_TILT 10094853
#define UVC_CTRL_RELATIVE_ZOOM 10094863

static struct uvc_control_info uvc_ctrls[] = {
    static struct uvc_control_mapping uvc_ctrl_mappings[] = {
    {
         .id = V4L2_CID_PAN_RELATIVE,
         .name = "Pan (Relative)",
         .entity = UVC_GUID_UVC_CAMERA,
         .selector = UVC_CT_PANTILT_RELATIVE_CONTROL,
         .size = 16,
         .offset = 0,
         .v4l2_type = V4L2_CTRL_TYPE_INTEGER,
         .data_type = UVC_CTRL_DATA_TYPE_SIGNED,
         .get = uvc_ctrl_get_rel_speed,
         .set = uvc_ctrl_set_rel_speed,
     },
     {
        .id = V4L2_CID_TILT_RELATIVE,
        .name = "Tilt (Relative)",
        .entity = UVC_GUID_UVC_CAMERA,
        .selector = UVC_CT_PANTILT_RELATIVE_CONTROL,
        .size = 16,
        .offset = 16,
        .v4l2_type = V4L2_CTRL_TYPE_INTEGER,
        .data_type = UVC_CTRL_DATA_TYPE_SIGNED,
        .get = uvc_ctrl_get_rel_speed,
        .set = uvc_ctrl_set_rel_speed,
     },
    }
}

static __s32 uvc_ctrl_get_rel_speed(struct uvc_control_mapping *mapping,
 __u8 query, const __u8 *data)
{
    int first = mapping->offset / 8;
    __s8 rel = (__s8)data[first];

    switch (query) {
     case UVC_GET_CUR:
     return (rel == 0) ? 0 : (rel > 0 ? data[first+1]
     : -data[first+1]);
     case UVC_GET_MIN:
     return -data[first+1];
     case UVC_GET_MAX:
     case UVC_GET_RES:
     case UVC_GET_DEF:
     default:
     return data[first+1];
    }
}

static void uvc_ctrl_set_rel_speed(struct uvc_control_mapping *mapping,
 __s32 value, __u8 *data)
{
    int first = mapping->offset / 8;

    data[first] = value == 0 ? 0 : (value > 0) ? 1 : 0xff;
    data[first+1] = min_t(int, abs(value), 0xff);
}

在映射集合里面添加相對(duì)控制參數(shù)，還要添加控制和獲取速度的方法慷蠕。

到這里上層編寫和底層定制基本完成珊拼。

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