Source code-sample program for capturing and using framebuffer Based on the UVC camera of v4l2

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <assert.h>#include <getopt.h>  #include <fcntl.h>  #include <unistd.h>#include <errno.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/time.h>#include <sys/mman.h>#include <sys/ioctl.h>#include <asm/types.h>#include <linux/videodev2.h>#include <linux/fb.h>#define CLEAR(x) memset (&(x), 0, sizeof (x))struct buffer {void * start;size_t length;};static char * dev_name = NULL;static int fd = -1;struct buffer * buffers = NULL;static unsigned int n_buffers = 0;static int time_in_sec_capture=5;static int fbfd = -1;static struct fb_var_screeninfo vinfo;static struct fb_fix_screeninfo finfo;static char *fbp=NULL;static long screensize=0;static void errno_exit (const char * s){fprintf (stderr, "%s error %d, %s\n",s, errno, strerror (errno));exit (EXIT_FAILURE);}static int xioctl (int fd,int request,void * arg){int r;do r = ioctl (fd, request, arg);while (-1 == r && EINTR == errno);return r;}inline int clip(int value, int min, int max) {return (value > max ? max : value < min ? min : value);}static void process_image (const void * p){//ConvertYUVToRGB32unsigned char* in=(char*)p;int width=640;int height=480;int istride=1280;int x,y,j;int y0,u,y1,v,r,g,b;long location=0;for ( y = 100; y < height + 100; ++y) {for (j = 0, x=100; j < width * 2 ; j += 4,x +=2) {location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +(y+vinfo.yoffset) * finfo.line_length;y0 = in[j];u = in[j + 1] - 128;                y1 = in[j + 2];        v = in[j + 3] - 128;        r = (298 * y0 + 409 * v + 128) >> 8;g = (298 * y0 - 100 * u - 208 * v + 128) >> 8;b = (298 * y0 + 516 * u + 128) >> 8;fbp[ location + 0] = clip(b, 0, 255);fbp[ location + 1] = clip(g, 0, 255);fbp[ location + 2] = clip(r, 0, 255);    fbp[ location + 3] = 255;    r = (298 * y1 + 409 * v + 128) >> 8;g = (298 * y1 - 100 * u - 208 * v + 128) >> 8;b = (298 * y1 + 516 * u + 128) >> 8;fbp[ location + 4] = clip(b, 0, 255);fbp[ location + 5] = clip(g, 0, 255);fbp[ location + 6] = clip(r, 0, 255);    fbp[ location + 7] = 255;    }in +=istride;}}static int read_frame (void){struct v4l2_buffer buf;unsigned int i;CLEAR (buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;if (-1 == xioctl (fd, VIDIOC_DQBUF, &buf)) {switch (errno) {case EAGAIN:return 0;case EIO:    default:errno_exit ("VIDIOC_DQBUF");}}assert (buf.index < n_buffers);assert (buf.field ==V4L2_FIELD_NONE);process_image (buffers[buf.index].start);if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))errno_exit ("VIDIOC_QBUF");return 1;}static void run (void){unsigned int count;int frames;frames = 30 * time_in_sec_capture;while (frames-- > 0) {for (;;) {fd_set fds;struct timeval tv;int r;FD_ZERO (&fds);FD_SET (fd, &fds);tv.tv_sec = 2;tv.tv_usec = 0;r = select (fd + 1, &fds, NULL, NULL, &tv);if (-1 == r) {if (EINTR == errno)continue;errno_exit ("select");}if (0 == r) {fprintf (stderr, "select timeout\n");exit (EXIT_FAILURE);}if (read_frame ())break;}}}static void stop_capturing (void){enum v4l2_buf_type type;type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (-1 == xioctl (fd, VIDIOC_STREAMOFF, &type))errno_exit ("VIDIOC_STREAMOFF");}static void start_capturing (void){unsigned int i;enum v4l2_buf_type type;for (i = 0; i < n_buffers; ++i) {struct v4l2_buffer buf;CLEAR (buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = i;if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))errno_exit ("VIDIOC_QBUF");}type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (-1 == xioctl (fd, VIDIOC_STREAMON, &type))errno_exit ("VIDIOC_STREAMON");}static void uninit_device (void){unsigned int i;for (i = 0; i < n_buffers; ++i)if (-1 == munmap (buffers[i].start, buffers[i].length))errno_exit ("munmap");if (-1 == munmap(fbp, screensize)) {printf(" Error: framebuffer device munmap() failed.\n");exit (EXIT_FAILURE) ;}    free (buffers);}static void init_mmap (void){struct v4l2_requestbuffers req;//mmap framebufferfbp = (char *)mmap(NULL,screensize,PROT_READ | PROT_WRITE,MAP_SHARED ,fbfd, 0);if ((int)fbp == -1) {printf("Error: failed to map framebuffer device to memory.\n");exit (EXIT_FAILURE) ;}memset(fbp, 0, screensize);CLEAR (req);req.count = 4;req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;req.memory = V4L2_MEMORY_MMAP;if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {if (EINVAL == errno) {fprintf (stderr, "%s does not support memory mapping\n", dev_name);exit (EXIT_FAILURE);} else {errno_exit ("VIDIOC_REQBUFS");}}if (req.count < 4) {    //if (req.count < 2)fprintf (stderr, "Insufficient buffer memory on %s\n",dev_name);exit (EXIT_FAILURE);}buffers = calloc (req.count, sizeof (*buffers));if (!buffers) {fprintf (stderr, "Out of memory\n");exit (EXIT_FAILURE);}for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {struct v4l2_buffer buf;CLEAR (buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = n_buffers;if (-1 == xioctl (fd, VIDIOC_QUERYBUF, &buf))errno_exit ("VIDIOC_QUERYBUF");buffers[n_buffers].length = buf.length;buffers[n_buffers].start =mmap (NULL,buf.length,PROT_READ | PROT_WRITE ,MAP_SHARED,fd, buf.m.offset);if (MAP_FAILED == buffers[n_buffers].start)errno_exit ("mmap");}}static void init_device (void){struct v4l2_capability cap;struct v4l2_cropcap cropcap;struct v4l2_crop crop;struct v4l2_format fmt;unsigned int min;// Get fixed screen informationif (-1==xioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {printf("Error reading fixed information.\n");exit (EXIT_FAILURE);}// Get variable screen informationif (-1==xioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {printf("Error reading variable information.\n");exit (EXIT_FAILURE);}screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;if (-1 == xioctl (fd, VIDIOC_QUERYCAP, &cap)) {if (EINVAL == errno) {fprintf (stderr, "%s is no V4L2 device\n",dev_name);exit (EXIT_FAILURE);} else {errno_exit ("VIDIOC_QUERYCAP");}}if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {fprintf (stderr, "%s is no video capture device\n",dev_name);exit (EXIT_FAILURE);}if (!(cap.capabilities & V4L2_CAP_STREAMING)) {fprintf (stderr, "%s does not support streaming i/o\n",dev_name);exit (EXIT_FAILURE);}CLEAR (cropcap);cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (0 == xioctl (fd, VIDIOC_CROPCAP, &cropcap)) {crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;crop.c = cropcap.defrect;if (-1 == xioctl (fd, VIDIOC_S_CROP, &crop)) {switch (errno) {case EINVAL:    break;default:break;}}}else {     }CLEAR (fmt);fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;fmt.fmt.pix.width = 640;  fmt.fmt.pix.height = 480;fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;fmt.fmt.pix.field = V4L2_FIELD_NONE;if (-1 == xioctl (fd, VIDIOC_S_FMT, &fmt))errno_exit ("VIDIOC_S_FMT");init_mmap ();}static void close_device (void){if (-1 == close (fd))errno_exit ("close");fd = -1;close(fbfd);}static void open_device (void){struct stat st;  if (-1 == stat (dev_name, &st)) {fprintf (stderr, "Cannot identify '%s': %d, %s\n",dev_name, errno, strerror (errno));exit (EXIT_FAILURE);}if (!S_ISCHR (st.st_mode)) {fprintf (stderr, "%s is no device\n", dev_name);exit (EXIT_FAILURE);}//open framebufferfbfd = open("/dev/fb0", O_RDWR);if (fbfd==-1) {printf("Error: cannot open framebuffer device.\n");exit (EXIT_FAILURE);}//open camerafd = open (dev_name, O_RDWR| O_NONBLOCK, 0);if (-1 == fd) {fprintf (stderr, "Cannot open '%s': %d, %s\n",dev_name, errno, strerror (errno));exit (EXIT_FAILURE);}}static void usage (FILE * fp,int argc,char ** argv){fprintf (fp,"Usage: %s [options]\n\n""Options:\n""-d | --device name Video device name [/dev/video]\n""-h | --help Print this message\n""-t | --how long will display in seconds\n""",argv[0]);}static const char short_options [] = "d:ht:";static const struct option long_options [] = {{ "device", required_argument, NULL, 'd' },{ "help", no_argument, NULL, 'h' },{ "time", no_argument, NULL, 't' },{ 0, 0, 0, 0 }};int main (int argc,char ** argv){dev_name = "/dev/video0";for (;;)  {int index;int c;c = getopt_long (argc, argv,short_options, long_options,&index);if (-1 == c)break;switch (c) {case 0:break;case 'd':dev_name = optarg;break;case 'h':usage (stdout, argc, argv);exit (EXIT_SUCCESS);case 't':time_in_sec_capture = atoi(optarg);break;default:usage (stderr, argc, argv);exit (EXIT_FAILURE);}}open_device ();init_device ();start_capturing ();run ();stop_capturing ();uninit_device ();close_device ();exit (EXIT_SUCCESS);return 0;}