Linux Framebuffer编程，应用程序需要知道Framebuffer设备的相关参数，必须通过ioctl()系统调用来完成。在头文件中定义了所有的ioctl命令字，不过，最常用的ioctl命令字是下面这两个：FBIOGET_FSCREENINFO和FBIOGET_VSCREENINFO。
前者返回与Framebuffer有关的固定的信息，比如图形硬件上实际的帧缓存空间的大小、能否硬件加速等信息。
而后者返回的是与Framebuffer有关的可变信息。可变的信息就是指Framebuffer的长度、宽度以及颜色深度等信息。

控制framebuffer设备的一般步骤如下：
1） 打开设备，映射framebuffer
2）依照硬件要求，准备好数据
3）把数据复制到framebuffer

打开设备，映射framebuffe
   static void *fbbuf;  
   int openfb(char *devname)  
   {  
       int fd;  
       fd = open(devname, O_RDWR);  
       if (ioctl(fd, FBIOGET_VSCREENINFO, &fbvar) < 0)  
           return -1;  
       bpp = fbvar.bits_per_pixel;  
       screen_size = fbvar.xres * fbvar.yres * bpp / 8;  
       fbbuf = mmap(0, screen_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);  
       return fd;  
   }     

数据准备，假设lcd控制器被初始化为565，16bit格式的
   static inline int  make_pixel(unsigned int a, unsigned int r, unsigned int g, unsigned int b)  
   {  
       return (unsigned int)(((r>>3)<<11)|((g>>2)<<5|(b>>3)));  
   }

把想要显示的数据复制到framebuffer
   static void fill_pixel(unsigned int pixel, int x0, int y0, int w, int h)  
   {  
       int i, j;  
       unsigned short *pbuf = (unsigned short *)fbbuf;  
       for (i = y0; i < h; i ++) {  
           for (j = x0; j < w; j ++) {  
               pbuf[i * screen_width + j] = pixel;  
           }  
       }  
   }
以上就是Linux Framebuffer编程的过程。

#include <asm/types.h>         
#include <fcntl.h>             
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <linux/fb.h>
#include <sys/time.h>
static void *fbbuf;
unsigned int bpp;
unsigned int screen_size;
struct fb_var_screeninfo fbvar;
struct fb_fix_screeninfo finfo;
int openfb(char *devname)
{
   int fd;
   fd = open(devname, O_RDWR);
   if (ioctl(fd, FBIOGET_VSCREENINFO, &fbvar) < 0)
       return -1;
   printf(“the clock is %d\n”, fbvar.pixclock);
   bpp = fbvar.bits_per_pixel;
   screen_size = fbvar.xres * fbvar.yres * bpp / 8;
   fbbuf = mmap(0, screen_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
   return fd;
}
static inline int  make_pixel(unsigned int a, unsigned int r, unsigned int g, unsigned int b)
{
   return (unsigned int)(((r>>3)<<11)|((g>>2)<<5|(b>>3)));
}
static void fill_pixel(unsigned int pixel, int x0, int y0, int w, int h)
{
   int i, j;
   unsigned short *pbuf = (unsigned short *)fbbuf;
   for (i = y0; i < h; i ++) {
       for (j = x0; j < w; j ++) {
           pbuf[i * 240 + j] = pixel;
       }
   }
}
int main () {
   unsigned int r, g, b;
   int fp=0;
   unsigned int count;

   r = 0;
   g = 0;
   b = 0;
   fp = openfb (“/dev/fb0″);

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

   while(1) {
       for (count = 0; count < 100; count++) {
           r = 0xff;
           fill_pixel(make_pixel(0, r, g, b), 0, 0, 240, 320);
       }
      for (count = 0; count < 100; count++) {
           r = 0×00;
           fill_pixel(make_pixel(0, r, g, b), 0, 0, 240, 320);
      }
   }
   return 0;
}