framebuff 显示子系统

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


int main () {
 int fp=0;
 struct fb_var_screeninfo vinfo;
 struct fb_fix_screeninfo finfo;
 long screensize=0;
 char *fbp = 0;
 int x = 0, y = 0;
 long location = 0;
 fp = open ("/dev/fb0",O_RDWR);


 if (fp < 0){
  printf("Error : Can not open framebuffer device/n");
  exit(1);
 }


 if (ioctl(fp,FBIOGET_FSCREENINFO,&finfo)){
  printf("Error reading fixed information/n");
  exit(2);
 }
 
 if (ioctl(fp,FBIOGET_VSCREENINFO,&vinfo)){
  printf("Error reading variable information/n");
  exit(3);
 }


  screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
 /*这就是把fp所指的文件中从开始到screensize大小的内容给映射出来，得到一个指向这块空间的指针*/
 fbp =(char *) mmap (0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fp,0);
   if ((int) fbp == -1)
     {
        printf ("Error: failed to map framebuffer device to memory./n");
        exit (4);
     }
/*这是你想画的点的位置坐标,(0，0)点在屏幕左上角*/
  x = 0;
  y = 0;
  location = x * (vinfo.bits_per_pixel / 8) + y  *  finfo.line_length;


  *(fbp + location) = value;  /*直接填充赋值来显示*/
 
  munmap (fbp, screensize); /*解除映射*/
  close (fp);    /*关闭文件*/
  return 0;


}