luvcview分析--1.环境搭建

一. 源码编译及目标
1.luvcview源码下载 

cong@msi:/tmp$  sudo apt-cache showsrc luvcview //a.查看有没有这个源码包
cong@msi:/tmp$ sudo apt-get source luvcview //b. 这就在当前目录下
cong@msi:/tmp$ ls
  luvcview_0.2.6-6.dsc luvcview-0.2.6 luvcview_0.2.6.orig.tar.gz luvcview_0.2.6-6.debian.tar.gz

2. luvcview编译

cong@msi:/work/test/busytest/luvcview-0.2.6$ make                  //直接make就可以了
Package libv4l2 was not found in the pkg-config search path.       //提示libv4l2包没有找到
Perhaps you should add the directory containing `libv4l2.pc'
No package 'libv4l2' found
v4l2uvc.c:28:21: fatal error: libv4l2.h: No such file or directory   //缺少libv4l2头文件
 #include <libv4l2.h>
cong@msi:/work/test/busytest/luvcview-0.2.6$ sudo apt-cache search libv4l2   //查找libv4l2包
  libv4l-dev - Collection of video4linux support libraries (development files)
cong@msi:/work/test/busytest/luvcview-0.2.6$ sudo apt-get install libv4l-dev  //安装libv4l2-dev

安装好libv4l2之后就可以编译出libvucview了
3. libv4l库的编译

libv4l的库源码下载地址:
http://people.atrpms.net/~hdegoede/

cong@msi:/work/libv4l2/libv4l-0.6.1$ ls
include  libv4l2  libv4lconvert  Makefile  README

cong@msi:/work/libv4l2/libv4l-0.6.1$ make LINKTYPE=static //直接make就可以了，这儿是编成静态库

4. libv4l库的使用

Makefile中:
CFLAGS=-g -O0 -I/work/test/uvcview/libv4l2/libv4l-0.6.1/include               //添加include路径
V4L2LIBS = -L/work/test/uvcview/libv4l2/libv4l-0.6.1/libv4l2 -lv4l2 \         //添加库的链接路径
           -L/work/test/uvcview/libv4l2/libv4l-0.6.1/libv4lconvert/ -lv4lconvert -lrt -lm

注意:
a. 出现undefined reference to `shm_open',是因为libv4l2库中用到了,需要在编译时加上-lrt
b. 出现undefined reference to `powf'，是因为libv4l2库中用到了,需要在编译时加上-lm
c. 为了防止系统中己安装的v4l2库的干扰,把v4l2删掉: sudo apt-get remove libv4l-dev 
5. 目标
目标是通过分析luvcview,自己动手写一个luvcview,这不是再次造轮子,而是一个学习并提高的过程。

---

二. 测试demo
2.1 check
获取camera所支持的视频格式

cong@msi:/work/test/uvcview/1check$ cat check.c
#include "utils.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/videodev2.h>

#define VIDEO_DEVICE "/dev/video0"
int main ( int argc, char *argv[] )
{
    int fd;
    int ret = 0;
    struct v4l2_capability cap;
    struct v4l2_fmtdesc fmt;
    if( (fd = v4l2_open(VIDEO_DEVICE,O_RDWR)) == -1)       //打开设备
    {
        dbmsg("error: %s", strerror(errno));
        return 0;
    }
    memset(&cap, 0, sizeof(struct v4l2_capability));
    if( (ret = v4l2_ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0))  //查询设备属性
    {
        dbmsg("error: %s", strerror(errno));
        return 0;
    }
    //接下来就可以进行一系列的判断了
    //cap.capabilities & V4L2_CAP_VIDEO_CAPTURE    //判断是否支持图像获取
    //cap.capabilities & V4L2_CAP_STREAMING        //是否具有数据流控制模式
    //cap.capabilities & V4L2_CAP_READWRITE        //是否支持 read和write I/O操作函数
    memset(&fmt, 0, sizeof(struct v4l2_fmtdesc));
    fmt.index = 0;
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while ((ret = v4l2_ioctl(fd, VIDIOC_ENUM_FMT, &fmt)) == 0) {    //获取当前视频设备支持的视频格式
            printf("{ pixelformat = '%c%c%c%c', description = '%s' }\n",
                    fmt.pixelformat & 0xFF, (fmt.pixelformat >> 8) & 0xFF,
                    (fmt.pixelformat >> 16) & 0xFF, (fmt.pixelformat >> 24) & 0xFF,
                    fmt.description);
            if(ret != 0)
                printf("  Unable to enumerate frame sizes.\n");
        fmt.index++;
    }
    return EXIT_SUCCESS;
}

b. Makefile

cong@msi:/work/test/uvcview/1check$ cat Makefile
EXE=check
CC=gcc
SRC=$(wildcard *.c)
#OBJ=$(SRC:.c=.o)
OBJ=$(patsubst %.c,%.o,$(SRC))
DEP=$(patsubst %.c,.%.d,$(SRC))
CFLAGS=-g -O0 -I/work/test/uvcview/libv4l2/libv4l-0.6.1/include
#V4L2LIBS = $(shell pkg-config --libs libv4l2)
V4L2LIBS = -L/work/test/uvcview/libv4l2/libv4l-0.6.1/libv4l2 -lv4l2 \
         -L/work/test/uvcview/libv4l2/libv4l-0.6.1/libv4lconvert/ -lv4lconvert \
         -lrt -lm
$(EXE):$(OBJ)
    $(CC) $(CFLAGS) $^ -o $@ $(V4L2LIBS)

$(DEP):.%.d:%.c
    @set -e; rm -f $@; \
    $(CC) -MM  $< > $@.$$$$; \
    sed 's,/($*/)/.o[ :]*,/1.o $@ : ,g' < $@.$$$$ > $@; \
    rm -f $@.$$$$

-include $(DEP)
clean:
    @rm $(EXE) $(OBJ) $(DEP) -f

1check.rar (下载后改名为1check.tar.gz)
c.运行结果

cong@msi:/work/test/uvcview/1check$ ./check
libv4l2.c:v4l2_open[477]:        //v4l2库打印的
libv4lconvert: warning more framesizes then I can   //v4l2库打印的
libv4lconvert: warning more framesizes then I can   //v4l2库打印的
{ pixelformat = 'YUYV', description = 'YUV 4:2:2 (YUYV)' }
{ pixelformat = 'MJPG', description = 'MJPEG' }
{ pixelformat = 'RGB3', description = 'RGB3' }
{ pixelformat = 'BGR3', description = 'BGR3' }
{ pixelformat = 'YU12', description = 'YU12' }
{ pixelformat = 'YV12', description = 'YV12' }