craspberry-picameraframebufferv4l2
Copying frames from camera (/dev/video0) to framebuffer (/dev/fb0) gives unexpected result
I have been trying to show frame from raspberry camera to screen with near best performance, and after research I found that the best way could be to use V4L2 library to directly communicate to drivers.
In the next section I present my code. It could characterize to be longer for Stack overflow, but I commented every block of code, so It can be more understandable.
#include <errno.h>
#include <fcntl.h>
#include <linux/videodev2.h>
#include <linux/fb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#define CAM_WIDTH 1280
#define CAM_HEIGHT 720
#define CAM_FORMAT (v4l2_fourcc('B','G','R','A'))
#define CAM_BUFFERS 1
int main(void)
{
int cam_fd;
int fb_fd;
struct v4l2_capability cap;
struct v4l2_requestbuffers reqbuf;
struct v4l2_format fmt;
struct v4l2_buffer buffinfo;
enum v4l2_buf_type bufftype;
char *cam_buffers[6];
int cam_buffer_size;
int cam_buffer_index = -1;
char *fb_p;
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
/* Setting framebuffer */
fb_fd = open("/dev/fb0", O_RDWR);
if(!fb_fd)
{
fprintf(stderr, "%s:%i: Unable to open framebuffer\n", __FILE__, __LINE__);
return -1;
}
ioctl(fb_fd, FBIOGET_FSCREENINFO, &finfo);
if(ioctl(fb_fd, FBIOGET_VSCREENINFO, &vinfo) == -1)
{
fprintf(stderr, "%s:%i: Unable to get framebuffer info\n", __FILE__, __LINE__);
return -1;
}
printf("Framebuffer: resolution %dx%d with %dbpp\n\r", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);
fb_p = (char*)mmap(0, vinfo.xres*vinfo.yres*4, PROT_READ | PROT_WRITE, MAP_SHARED, fb_fd, 0);
memset(fb_p, 0, vinfo.xres*vinfo.yres*4);
/* Setting camera */
cam_fd = open("/dev/video0", O_RDWR | O_NONBLOCK, 0);
if(!cam_fd){
fprintf(stderr, "%s:%i: Couldn't open device\n", __FILE__, __LINE__);
return -1;
}
if(ioctl(cam_fd, VIDIOC_QUERYCAP, &cap))
{
fprintf(stderr, "%s:%i: Couldn't retreive device capabilities\n", __FILE__, __LINE__);
return -1;
}
if(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE == 0)
{
fprintf(stderr, "%s:%i: Device is not a capture device\n", __FILE__, __LINE__);
return -1;
}
if(cap.capabilities & V4L2_CAP_STREAMING == 0)
{
fprintf(stderr, "%s:%i: Device is not available for streaming", __FILE__, __LINE__);
return -1;
}
/* Set image format */
memset(&fmt, 0, sizeof(fmt));
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = CAM_WIDTH;
fmt.fmt.pix.height = CAM_HEIGHT;
fmt.fmt.pix.pixelformat = CAM_FORMAT;
fmt.fmt.pix.field = V4L2_FIELD_NONE;
if(ioctl(cam_fd, VIDIOC_S_FMT, &fmt) == -1)
{
fprintf(stderr, "%s:%i: Unable to set image format\n", __FILE__, __LINE__);
return -1;
}
cam_buffer_size = fmt.fmt.pix.sizeimage;
/* Request buffers */
memset(&reqbuf, 0, sizeof(reqbuf));
reqbuf.count = CAM_BUFFERS;
reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
reqbuf.memory = V4L2_MEMORY_MMAP;
if(ioctl(cam_fd, VIDIOC_REQBUFS, &reqbuf) == -1)
{
fprintf(stderr, "%s:%i: Mmap streaming not supported\n", __FILE__, __LINE__);
return -1;
}
if(reqbuf.count != CAM_BUFFERS)
{
fprintf(stderr, "%S:%i: Not all requared buffers are allocated\n", __FILE__, __LINE__);
return -1;
}
/* Query and Mmap buffers */
for (int i=0; i < CAM_BUFFERS; i++)
{
memset(&buffinfo, 0, sizeof(buffinfo));
buffinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffinfo.memory = V4L2_MEMORY_MMAP;
buffinfo.index = i;
if(ioctl(cam_fd, VIDIOC_QUERYBUF, &buffinfo) == -1)
{
fprintf(stderr, "%s:%i: Unable to query buffers\n", __FILE__, __LINE__);
return -1;
}
cam_buffers[i] = mmap(NULL, buffinfo.length, PROT_READ | PROT_WRITE, MAP_SHARED, cam_fd, buffinfo.m.offset);
if(cam_buffers[i] == MAP_FAILED)
{
fprintf(stderr, "%s:%i: Unable to enqueue buffers\n", __FILE__, __LINE__);
return -1;
}
}
/* Enqueue buffers */
for (int i=0; i < CAM_BUFFERS; i++)
{
memset(&buffinfo, 0, sizeof(buffinfo));
buffinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffinfo.memory = V4L2_MEMORY_MMAP;
buffinfo.index = i;
if(ioctl(cam_fd, VIDIOC_QBUF, &buffinfo) == -1)
{
fprintf(stderr, "%s:%i: Unable to enqueue buffers\n", __FILE__, __LINE__);
return -1;
}
}
/* Start Streaming */
bufftype = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(ioctl(cam_fd, VIDIOC_STREAMON, &bufftype) == -1)
{
fprintf(stderr, "%s:%i: Unable to start streaming\n", __FILE__, __LINE__);
return -1;
}
while(1)
{
fd_set fds;
struct timeval tv;
int r;
FD_ZERO(&fds);
FD_SET(cam_fd, &fds);
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(cam_fd+1, &fds, NULL, NULL, &tv);
if (r == -1) {
if (errno = EINTR)
continue;
fprintf(stderr, "%s:%i: Call to select() failed\n", __FILE__, __LINE__);
return -1;
}
if (r == 0) {
fprintf(stderr, "%s:%i: Call to select() timeout\n", __FILE__, __LINE__);
continue;
}
if (!FD_ISSET(cam_fd, &fds))
continue;
memset(&buffinfo, 0, sizeof(buffinfo));
buffinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffinfo.memory = V4L2_MEMORY_MMAP;
if(ioctl(cam_fd, VIDIOC_DQBUF, &buffinfo) == -1) {
if(errno == EAGAIN)
continue;
fprintf(stderr, "%s:%i: Unable to dequeue buffer\n", __FILE__, __LINE__);
return -1;
}
cam_buffer_index = buffinfo.index;
memcpy(fb_p, cam_buffers[cam_buffer_index], vinfo.xres*vinfo.yres*4);
memset(&buffinfo, 0, sizeof(buffinfo));
buffinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffinfo.memory = V4L2_MEMORY_MMAP;
buffinfo.index = cam_buffer_index;
if(ioctl(cam_fd, VIDIOC_QBUF, &buffinfo) == -1) {
fprintf(stderr, "%s:%i: Unable to enqueue buffer\n", __FILE__, __LINE__);
return -1;
}
}
return 0;
}
The output on my screen, You can see on next image:
I just cannot understand why the output is like that. I typed fbset -i command to check info about my framebuffer it says: Its 1280x720, has 32 bpp, and in rgba section it says 8/16, 8/8, 8/0, 8/24 (which should mean its in BGRA format). Does anyone encountered this 'weird' behavior before and know what is going on? I have look for logical errors in my code, but was unable to find where did I make mistake.
Also, If somebody have suggestion about this topic I am researching right now, Some advice would really help.
Solution
I figured out what was the problem. I typed v4l2-ctl --list-formats to check which formats my camera is supporting and there is no BGRA, so it possibly choose one of the possible options: YU12, YUYV, RGB3, JPEG, H264, MJPG, YVYU, VYUY, UYVY, NV12, BGR3, YV12, NV21 and RX24. I chose BGR3, copy it to framebuffer with 2 for loops adding alpha value after every BGR component and got right colored image!
Here Is block of code to populate framebuffer:
int offset_data = 0;
for (int i = 0; i < vinfo.yres; i++)
{
for (int j = 0; j < vinfo.xres*4; j+=4)
{
int idx = i*vinfo.xres*4 + j;
fb_p[idx] = cam_buffers[cam_buffer_index][offset_data+0];
fb_p[idx+1] = cam_buffers[cam_buffer_index][offset_data+1];
fb_p[idx+2] = cam_buffers[cam_buffer_index][offset_data+2];
fb_p[idx+3] = 0;
offset_data += 3;
}
}
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