常用的USB拍照功能代码：
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#include "uvcTest.h"
#define FILE_VIDEO "/dev/video0"
#define JPG "./p_w_picpath%d.jpg"
BUFTYPE *usr_buf;
static unsigned int n_buffer = 0;
//set video capture ways(mmap)
int init_mmap(int fd)
{
//to request frame cache, contain requested counts
struct v4l2_requestbuffers reqbufs;
//request V4L2 driver allocation video cache
//this cache is locate in kernel and need mmap mapping
memset(&reqbufs, 0, sizeof(reqbufs));
reqbufs.count = 4;
reqbufs.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
reqbufs.memory = V4L2_MEMORY_MMAP;
if(-1 == ioctl(fd,VIDIOC_REQBUFS,&reqbufs)){
perror("Fail to ioctl 'VIDIOC_REQBUFS'");
exit(EXIT_FAILURE);
}
n_buffer = reqbufs.count;
printf("n_buffer = %d\n", n_buffer);
// usr_buf = (BUFTYPE *)calloc(reqbufs.count, sizeof(usr_buf));
usr_buf = new BUFTYPE[reqbufs.count*sizeof(BUFTYPE)];
if(usr_buf == NULL){
printf("Out of memory\n");
exit(-1);
}
//map kernel cache to user process
for(n_buffer = 0; n_buffer < reqbufs.count; ++n_buffer){
//stand for a frame
struct v4l2_buffer buf;
memset(&buf, 0, sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffer;
//check the information of the kernel cache requested
if(-1 == ioctl(fd,VIDIOC_QUERYBUF,&buf))
{
perror("Fail to ioctl : VIDIOC_QUERYBUF");
exit(EXIT_FAILURE);
}
usr_buf[n_buffer].length = buf.length;
usr_buf[n_buffer].start =
(char *)mmap(
NULL,
buf.length,
PROT_READ | PROT_WRITE,
MAP_PRIVATE,
fd,
buf.m.offset
);
if(MAP_FAILED == usr_buf[n_buffer].start)
{
perror("Fail to mmap");
exit(EXIT_FAILURE);
}
}
return 0;
}
//initial camera device
int init_camera_device(int fd)
{
//decive fuction, such as video input
struct v4l2_capability cap;
//video standard,such as PAL,NTSC
struct v4l2_standard std;
//frame format
struct v4l2_format tv_fmt;
//check control
struct v4l2_queryctrl query;
//detail control value
struct v4l2_fmtdesc fmt;
int ret;
//get the format of video supply
memset(&fmt, 0, sizeof(fmt));
fmt.index = 0;
//supply to p_w_picpath capture
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
// show all format of supply
printf("Support format:\n");
while(ioctl(fd, VIDIOC_ENUM_FMT, &fmt) == 0){
fmt.index++;
printf("pixelformat = ''%c%c%c%c''\ndescription = ''%s''\n",fmt.pixelformat & 0xFF, (fmt.pixelformat >> 8) & 0xFF,(fmt.pixelformat >> 16) & 0xFF, (fmt.pixelformat >> 24) & 0xFF,fmt.description);
}
//check video decive driver capability
ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
if(ret < 0){
perror("Fail to ioctl VIDEO_QUERYCAP");
exit(EXIT_FAILURE);
}
//judge wherher or not to be a video-get device
if(!(cap.capabilities & V4L2_BUF_TYPE_VIDEO_CAPTURE))
{
printf("The Current device is not a video capture device\n");
exit(-1);
}
//judge whether or not to supply the form of video stream
if(!(cap.capabilities & V4L2_CAP_STREAMING))
{
printf("The Current device does not support streaming i/o\n");
exit(EXIT_FAILURE);
}
//set the form of camera capture data
tv_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
tv_fmt.fmt.pix.width = 100;
tv_fmt.fmt.pix.height = 100;
tv_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
tv_fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
if (ioctl(fd, VIDIOC_S_FMT, &tv_fmt)< 0) {
printf("VIDIOC_S_FMT\n");
exit(-1);
close(fd);
}
//initial video capture way(mmap)
init_mmap(fd);
return 0;
}
int open_camera_device(const char *dev_name)
{
int fd;
QString devName =QString(QLatin1String(dev_name));
QString strDevName = QString("sudo chmod 777 %1").arg(devName);
qDebug()<<"strDevName"< 0)
{
for(;;)
{
fd_set fds;
struct timeval tv;
int r;
FD_ZERO(&fds);
FD_SET(fd,&fds);
/*Timeout*/
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(fd + 1,&fds,NULL,NULL,&tv);
if(-1 == r)
{
if(EINTR == errno)
continue;
perror("Fail to select");
exit(EXIT_FAILURE);
}
if(0 == r)
{
fprintf(stderr,"select Timeout\n");
exit(-1);
}
if(read_frame(fd,workOrder))
break;
}
}
return 0;
}
void stop_capture(int fd)
{
enum v4l2_buf_type type;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(-1 == ioctl(fd,VIDIOC_STREAMOFF,&type))
{
qDebug()<<"stop"<
