C程序实现在lcd 上全屏写 blue 色 及获取fb信息

（1） 打开设备 open("/dev/fb0",O_RDWR);

  (2)  获取framebuffer设备信息.ioctl(int fb,FBIOGET_FSCREENINFO,&finfo);

       ioctl函数是实现对设备的信息获取和设定，第一个参数为文件描述符，第二个参数为具体设备的参数，对于framebuffer,参数在linux/fb.h中定义的。

      #define FBIOGET_VSCREENINFO 0x4600   //获取设备无关的数据信息fb_var_screeninfo
      #define FBIOPUT_VSCREENINFO 0x4601   //设定设备无关的数据信息
      #define FBIOGET_FSCREENINFO 0x4602   //获取设备无关的常值信息fb_fix_screeninfo
      #define FBIOGETCMAP  0x4604        //获取设备无关颜色表信息
      #define FBIOPUTCMAP  0x4605       //设定设备无关颜色表信息
      #define FBIOPAN_DISPLAY  0x4606
      #define FBIO_CURSOR            _IOWR('F', 0x08, struct fb_cursor)

      第三个参数是存放信息的结构体或者缓冲区

(3)内存映射 mmap函数。头文件：sys/mman.h .常用用法：mmap(0,screensize,PROT_RD　｜PROT_WR,MAP_SHARED,int fb,0)返回映射的首地址。

 

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#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <stdlib.h>

int main()
{
        int fbfd = 0;
        struct fb_var_screeninfo vinfo;
        struct fb_fix_screeninfo finfo;
        long int screensize = 0;
        char *fbp = 0;
        int x = 0, y = 0;
        long int location = 0;
       int sav=0;
        /* open device*/
        fbfd = open("/dev/fb0", O_RDWR);
        if (!fbfd) {
                printf("Error: cannot open framebuffer device.\n");
                exit(1);
        }
        printf("The framebuffer device was opened successfully.\n");

        /* Get fixed screen information */
        if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
                printf("Error reading fixed information.\n");
                exit(2);
        }

        /* Get variable screen information */
        if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
                printf("Error reading variable information.\n");
                exit(3);
        }

/* show these information*/
printf("vinfo.xres=%d\n",vinfo.xres);
printf("vinfo.yres=%d\n",vinfo.yres);
printf("vinfo.bits_per_bits=%d\n",vinfo.bits_per_pixel);
printf("vinfo.xoffset=%d\n",vinfo.xoffset);
printf("vinfo.yoffset=%d\n",vinfo.yoffset);
printf("finfo.line_length=%d\n",finfo.line_length);

        /* Figure out the size of the screen in bytes */
        screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
        /* Map the device to memory */
        fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,

                fbfd, 0);      
        if ((int)fbp == -1) { printf("Error: failed to map framebuffer device to memory.\n"); exit(4);
        }
        printf("The framebuffer device was mapped to memory successfully.\n");

memset(fbp,0,screensize);
            /* Where we are going to put the pixel */
for(x=0;x<vinfo.xres;x++)
for(y=0;y<vinfo.yres;y++)

{
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
         (y+vinfo.yoffset) * finfo.line_length;

        *(fbp + location) = 0xff; /*  blue */
        *(fbp + location + 1) = 0x00;    
         }           
      munmap(fbp, screensize);  /* release the memory */
      close(fbfd);
      return 0;
}