我的环境是友善之臂的fire3，Ubuntu1604，使用的是uvc免驱摄像头
大致的工作流程如下
一、获取摄像头图片
1、打开摄像头
2、获取摄像头的一些信息，比如支持的格式等等
3、设置摄像头的一些参数，比如输出格式等等
4、申请缓冲区
5、内存映射
6、开始采集
二、将图片在lcd上显示出来
1、打开lcd的设备fb0，如果没有这个，恭喜。
2、获取一些lcd的信息，如lcd的长宽等
3、内存映射
4、将图片写进映射过来的内存。
由于我的摄像头选的是YUYV的输出格式，所以在从摄像头取得图片之后，还需要转换成rgb才行，因为lcd得写rgb才行。
下面是代码：
分为主要的摄像头读取文件以及一个framebuffer，lcd的显示文件。
1、摄像头读取文件
头文件
#ifndef _V4L2_H
#define _V4L2_H
#define DEV_PATH "/dev/video0"
#define BMP "./image.bmp"
#define YUYV "./image.yuv"
#define TURE 1
#define FALSE 0
#define N_BUFFER 4
struct buffer{
void* start;
unsigned int length;
};
/*V4L2初始化*/
void v4l2_init();
/*V4L2关闭*/
void v4l2_close();
#endif
C文件
#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/ioctl.h>
#include<stdlib.h>
#include<sys/mman.h>
#include<linux/types.h>
#include<linux/videodev2.h>
#include<string.h>
#include "V4l2.h"
#include "framebuffer.c"
static int fd;
struct buffer* buffers=NULL;
void v4l2_init(int width,int height){
/*打开设备*/
fd=open(DEV_PATH,O_RDWR);
if(fd==-1)
perror("open "),exit(-1);
/*读取设备信息*/
struct v4l2_capability cap;
int res=ioctl(fd, VIDIOC_QUERYCAP, &cap);
if(res==-1)
printf("read dev information error\n"),exit(-1);
else{
printf("driver:\t\t%s\n",cap.driver);
printf("card:\t\t%s\n",cap.card);
printf("bus_info:\t%s\n",cap.bus_info);
printf("version:\t%d\n",cap.version);
printf("capabilities:\t%x\n",cap.capabilities);
}
/*查询是否支持视频采集*/
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE)
printf("Device %s: supports capture.\n",DEV_PATH);
else
printf("Device not supports capture\n"),exit(-1);
if ((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING)
printf("Device %s: supports streaming.\n",DEV_PATH);
else
printf("Device not supports streaming\n"),exit(-1);
/*查询设备支持的图片输出格式*/
struct v4l2_fmtdesc fmtdesc;
fmtdesc.index=0;
fmtdesc.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
printf("Support format:\n");
while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1){
printf("%d.%s\n",fmtdesc.index+1,fmtdesc.description);
fmtdesc.index++;
}
/*设置帧格式,并检验*/
struct v4l2_format format;
format.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
format.fmt.pix.pixelformat=V4L2_PIX_FMT_YUYV;
format.fmt.pix.height=height;
format.fmt.pix.width=width;
format.fmt.pix.field=V4L2_FIELD_INTERLACED;
res=ioctl(fd,VIDIOC_S_FMT,&format);
if(res==-1)
printf("set up frame foramt failed\n"),exit(-1);
res=ioctl(fd,VIDIOC_G_FMT,&format);
if(res==-1)
printf("read frame format failed\n"),exit(-1);
printf("type:\t\t%d\n",format.type);
printf("pix.pixelformat:\t%c%c%c%c\n",format.fmt.pix.pixelformat & 0xFF, (format.fmt.pix.pixelformat >> 8) & 0xFF,(format.fmt.pix.pixelformat >> 16) & 0xFF, (format.fmt.pix.pixelformat >> 24) & 0xFF);
printf("pix.height:\t\t%d\n",format.fmt.pix.height);
printf("pix.width:\t\t%d\n",format.fmt.pix.width);
printf("pix.field:\t\t%d\n",format.fmt.pix.field);
/*申请缓冲区*/
struct v4l2_requestbuffers req;
struct v4l2_buffer buf;
req.count=N_BUFFER;
req.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory=V4L2_MEMORY_MMAP;
res=ioctl(fd,VIDIOC_REQBUFS,&req);
if(res==-1)
printf("memory request failed\n"),exit(-1);
buffers=malloc(req.count*sizeof(struct buffer));
if(!buffers)
printf("out of memory!\n"),exit(-1);
for(int i=0;i<req.count;++i){
buf.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory=V4L2_MEMORY_MMAP;
buf.index=i;
res=ioctl(fd,VIDIOC_QUERYBUF,&buf);
if(res==-1)
printf("query buffer error\n"),exit(-1);
buffers[i].length=buf.length;
buffers[i].start=mmap(NULL,buf.length,PROT_READ|PROT_WRITE,MAP_SHARED,fd,buf.m.offset);
if (buffers[i].start == MAP_FAILED)
printf("buffer map error\n"),exit(-1);
}
//将所有缓冲区挂入输入队列
for (int i = 0;i < req.count;++i){
buf.index =i;
ioctl(fd, VIDIOC_QBUF, &buf);
}
/*开始采集图像*/
enum v4l2_buf_type type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
res=ioctl (fd, VIDIOC_STREAMON, &type);
if(res==-1)
printf("error to start\n");
else
printf("start to act!\n");
}
void v4l2_close(void){
if(fd == -1)
printf("close failed\n"),exit(-1);
enum v4l2_buf_type type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
/*关闭视频采集*/
int res=ioctl(fd,VIDIOC_STREAMOFF,&type);
if(res==-1)
printf("close stream failed\n"),exit(-1);
else
printf("success to close stream\n");
/*解除内存映射*/
for(int i=0;i<N_BUFFER;i++){
if(munmap(buffers[i].start,buffers[i].length)==(void*)(-1))
printf("error to munmap\n"),exit(-1);
}
printf("success to munmap!\n");
/*释放内存*/
free(buffers);
printf("success to free!\n");
/*关闭文件描述符*/
close(fd);
printf("v4l2 success to close\n");
}
struct buffer* v4l2_get(){//VIDIOC_DQBUF有阻塞功能，无需等待
/* struct timeval tv;
fd_set fds;
FD_ZERO(&fds);
FD_SET(fd,&fds);
tv.tv_sec=2;
tv.tv_usec=0;
int res=select(fd+1,&fds,NULL,NULL,&tv);
if(res==-1)
printf("select error\n"),exit(-1);
else if(res==0)
printf("timeout\n"),exit(-1);
*/
struct v4l2_buffer buf;
struct buffer* buffer1=NULL;
memset(&buf,0,sizeof(buf));
buf.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory=V4L2_MEMORY_MMAP;
int res=ioctl(fd,VIDIOC_DQBUF,&buf);
if(res==-1){
printf("get error!\n");
v4l2_close();
exit(-1);
}
buffer1=&buffers[buf.index];
/*重新放入输入队列*/
res=ioctl(fd,VIDIOC_QBUF,&buf);
if(res!=0)
printf("error to put in input quene\n"),exit(-1);
return buffer1;
}
extern void* framebuffer;
extern int framex;
void yuyv_to_rgb24(unsigned char* yuv,int length,unsigned char *rgb){
unsigned int i;
unsigned int i1=0,j1=0;
unsigned char* y0=yuv+0;
unsigned char* u0=yuv+1;
unsigned char* y1=yuv+2;
unsigned char* v0=yuv+3;
unsigned char* r0=rgb+0;
unsigned char* g0=rgb+1;
unsigned char* b0=rgb+2;
unsigned char* r1=rgb+3;
unsigned char* g1=rgb+4;
unsigned char* b1=rgb+5;
rgb32_frame* frame=(rgb32_frame*)framebuffer;
double rt0=0,gt0=0,bt0=0,rt1=0,gt1=0,bt1=0;
for(i=0;i<=(length/4);i++){
bt0=1.164*(*y0-16)+2.017*(*u0-128);
gt0=1.164*(*y0-16)-0.813*(*v0-128)-0.392*(*u0-128);
rt0=1.164*(*y0-16)+1.596*(*v0-128);
bt1=1.164*(*y1-16)+2.018*(*u0-128);
gt1=1.164*(*y1-16)-0.813*(*v0-128)-0.392*(*u0-128);
rt1=1.164*(*y1-16)+1.596*(*v0-128);
if(rt0>255) rt0=255;
else if(rt0<0) rt0=0;
if(gt0>255) gt0=255;
else if(gt0<0) gt0=0;
if(bt0>255) bt0=255;
else if(bt0<0) bt0=0;
if(rt1>255) rt1=255;
else if(rt1<0) rt1=0;
if(gt1>255) gt1=255;
else if(gt1<0) gt1=0;
if(bt1>255) bt1=255;
else if(bt1<0) bt1=0;
*r0=(unsigned char)rt0;
*g0=(unsigned char)gt0;
*b0=(unsigned char)bt0;
*r1=(unsigned char)rt1;
*g1=(unsigned char)gt1;
*b1=(unsigned char)bt1;
frame[i1+j1].b=*r0;
frame[i1+j1].g=*g0;
frame[i1+j1].r=*b0;
frame[i1+j1+1].b=*r1;
frame[i1+j1+1].g=*g1;
frame[i1+j1+1].r=*b1;
j1+=2;
if(i%320==0){
j1=0;
i1+=framex;
}
yuv=yuv+4;
rgb=rgb+6;
if(yuv==NULL)
break;
y0=yuv;
u0=yuv+1;
y1=yuv+2;
v0=yuv+3;
r0=rgb+0;
g0=rgb+1;
b0=rgb+2;
r1=rgb+3;
g1=rgb+4;
b1=rgb+5;
}
}
void yuyv_to_rgb32(unsigned char* yuv,int length,unsigned char *rgb){
unsigned int i;
unsigned char* y0=yuv+0;
unsigned char* u0=yuv+1;
unsigned char* y1=yuv+2;
unsigned char* v0=yuv+3;
unsigned char* r0=rgb+0;
unsigned char* g0=rgb+1;
unsigned char* b0=rgb+2;
unsigned char* r1=rgb+4;
unsigned char* g1=rgb+5;
unsigned char* b1=rgb+6;
double rt0=0,gt0=0,bt0=0,rt1=0,gt1=0,bt1=0;
for(i=0;i<=(length/4);i++){
bt0=1.164*(*y0-16)+2.017*(*u0-128);
gt0=1.164*(*y0-16)-0.813*(*v0-128)-0.392*(*u0-128);
rt0=1.164*(*y0-16)+1.596*(*v0-128);
bt1=1.164*(*y1-16)+2.017*(*u0-128);
gt1=1.164*(*y1-16)-0.813*(*v0-128)-0.392*(*u0-128);
rt1=1.164*(*y1-16)+1.596*(*v0-128);
if(rt0>255) rt0=255;
else if(rt0<0) rt0=0;
if(gt0>255) gt0=255;
else if(gt0<0) gt0=0;
if(bt0>255) bt0=255;
else if(bt0<0) bt0=0;
if(rt1>255) rt1=255;
else if(rt1<0) rt1=0;
if(gt1>255) gt1=255;
else if(gt1<0) gt1=0;
if(bt1>255) bt1=255;
else if(bt1<0) bt1=0;
*r0=(unsigned char)rt0;
*g0=(unsigned char)gt0;
*b0=(unsigned char)bt0;
*r1=(unsigned char)rt1;
*g1=(unsigned char)gt1;
*b1=(unsigned char)bt1;
yuv=yuv+4;
rgb=rgb+8;
if(yuv==NULL)
break;
y0=yuv;
u0=yuv+1;
y1=yuv+2;
v0=yuv+3;
r0=rgb+0;
g0=rgb+1;
b0=rgb+2;
r1=rgb+4;
g1=rgb+5;
b1=rgb+6;
}
}
int main(){
struct buffer* yuv=NULL;
v4l2_init(640,480);
framebuffer_init();
void * pic=malloc(640*480*3);
while(1){
yuv=v4l2_get();
yuyv_to_rgb24(yuv->start,yuv->length,(unsigned char*)pic);
}
framebuffer_close();
v4l2_close();
}
2、framebuffer文件
头文件
#ifndef _FRAMEBUFFER_H
#define _FRAMEBUFFER_H
typedef struct{
unsigned char r;
unsigned char g;
unsigned char b;
unsigned char rgbReserved;
}rgb32;
typedef struct{
unsigned char r;
unsigned char g;
unsigned char b;
unsigned char rgbReserved;
}rgb32_frame;
typedef struct{
unsigned char r;
unsigned char g;
unsigned char b;
}rgb24;
typedef struct{
unsigned char r;
unsigned char g;
unsigned char b;
}rgb24_frame;
void framebuffer_init(void);
void framebuffer_write(void* img_buf,unsigned int img_width,unsigned int img_height,unsigned int img_bits);
void framebuffer_close(void);
#endif
C文件
#include "framebuffer.h"
#include<unistd.h>
#include<fcntl.h>
#include<linux/fb.h>
#include<linux/kd.h>
#include<sys/mman.h>
#include<sys/ioctl.h>
#include<stdlib.h>
#include<stdio.h>
static int frame_fd=-1;
void* framebuffer=NULL;
static int screensize=0;
int framex=0;
void framebuffer_init(void){
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
frame_fd = open("/dev/fb0" , O_RDWR);
if(frame_fd==-1)
perror("open frame buffer fail"),exit(-1);
// Get fixed screen information
if (ioctl(frame_fd, FBIOGET_FSCREENINFO, &finfo))
printf("Error reading fixed information.\n"),exit(-1);
// Get variable screen information
if (ioctl(frame_fd, FBIOGET_VSCREENINFO, &vinfo))
printf("Error reading variable information.\n"),exit(-1);
//这里把整个显存一起初始化（xres_virtual 表示显存的x，比实际的xres大,bits_per_pixel位深）
screensize = vinfo.xres_virtual * vinfo.yres_virtual * vinfo.bits_per_pixel / 8;
framex=vinfo.xres_virtual;
//获取实际的位色，这里很关键，后面转换和填写的时候需要
int framebpp = vinfo.bits_per_pixel;
printf("%dx%d, %d bpp screensize is %ld\n", vinfo.xres_virtual, vinfo.yres_virtual, vinfo.bits_per_pixel,screensize);
//映射出来，用户直接操作
framebuffer = mmap(0, screensize, PROT_READ | PROT_WRITE , MAP_SHARED ,frame_fd ,0 );
if(framebuffer == (void *)-1)
perror("memory map fail"),exit(-1);
}
//写入framebuffer img_buf:采集到的图片首地址 width：用户的宽 height：用户的高 bits：图片的位深
void framebuffer_write(void *img_buf, unsigned int img_width, unsigned int img_height, unsigned int img_bits){
int row, column;
int num = 0; //img_buf 中的某个像素点元素的下标
rgb32_frame *rgb32_fbp = (rgb32_frame *)framebuffer;
rgb24 *rgb24_img_buf = (rgb24 *)img_buf;
//防止摄像头采集宽高比显存大
if(screensize < img_width * img_height * img_bits / 8){
printf("the imgsize is too large\n"),exit(-1);
}
/*不同的位深度图片使用不同的显示方案*/
switch (img_bits){
case 24:
for(row = 0; row < img_height; row++){
for(column = 0; column < img_width; column++){
//由于摄像头分辨率没有帧缓冲大，完成显示后，需要强制换行，帧缓冲是线性的，使用row * vinfo.xres_virtual换行
rgb32_fbp[row * framex + column].r = rgb24_img_buf[num].b;
rgb32_fbp[row * framex + column].g = rgb24_img_buf[num].g;
rgb32_fbp[row * framex + column].b = rgb24_img_buf[num].r;
num++;
}
}
break;
default:
break;
}
}
void framebuffer_close(void){
munmap(framebuffer,screensize);
if(frame_fd==-1)
perror("file don't exit\n"),exit(-1);
close(frame_fd);
}
