Framebuffer编程

来源：互联网发布：sshd 知乎编辑：程序博客网时间：2024/05/22 06:05

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;
    intopenfb(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
    staticinline int make_pixel(unsigned int a, unsignedint r, unsigned int g, unsigned int b)
    {
       return (unsignedint)(((r>>3)<<11)|((g>>2)<<5|(b>>3)));
    }

把想要显示的数据复制到framebuffer
    static voidfill_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)
{
    intfd;
    fd =open(devname, O_RDWR);
    if(ioctl(fd, FBIOGET_VSCREENINFO, &fbvar)< 0)
       return -1;
    printf("theclock 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);
    returnfd;
}
static inline int make_pixel(unsigned int a,unsigned int r, unsigned int g, unsigned int b)
{
    return(unsignedint)(((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;
    unsignedshort *pbuf = (unsigned short *)fbbuf;
    for (i = y0;i < h; i ++) {
       for (j = x0; j < w; j ++) {
           pbuf[i * 240 + j] = pixel;
       }
    }
}
int main () {
    unsigned intr, g, b;
    intfp=0;
    unsigned intcount;

    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 = 0x00;
           fill_pixel(make_pixel(0, r, g, b), 0, 0, 240, 320);
      }
    }
    return0;
}

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