Linux Framebuffer编程实例源码介绍程序要获取Framebuffer设备的相关参数信息的话，就要通过ioctl()系统调用来完成。头文件中定义了所有的ioctl命令字，但最常用的ioctl命令字是下面这两个：FBIOGET_FSCREENINFO和FBIOGET_VSCREENINFO。
前一个返回与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。而后一个返回的是与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;
}