[转]基于FrameBuffer的直接写屏

[转]基于FrameBuffer的直接写屏

1.将FrameBuffer配置成800x600x16色的显示模式
在/boot/grub/menu.lst中的kernel加入vga=0x314
//test.c

#include  < stdio.h >
#include  < unistd.h >
#include  < sys / types.h >
#include  < sys / stat.h >
#include  < fcntl.h >
int  main( int  argc, char   ** argv){
  int  fb_fd = 0 ;
  char   * fbdev = " /dev/fb0 " ;
  if ((fd_fd = open(fbdev,O_RDWR)) < 0 ){
  printf( " open FrameBuffer device failed. " n " );
   return   - 1 ;
 }
 printf( " open FrameBuffer device successfully! " n " );
 close(fb_fd);
}

编译后执行一下，看看当前内核是否支持FrameBuffer机制.
设备打开成功后要获取相当的参数，使用ioctl，会填充以下结构体，
在linux/fb.h中定义的
struct fb_fix_screeninfo
struct fb_var_screeninfo
struct fb_cmap
从fs.h中可看出

#define FBIOGET_VSCREENINFO 0x4600
#define FBIOGET_FSCREENINFO 0x4602

我们就用这两条命令获取相当的参数信息
//test.c

#include  < stdio.h >
#include  < unistd.h >
#include  < sys / types.h >
#include  < sys / stat.h >
#include  < fcntl.h >
#include  < linux / fb.h >
int  main( int  argc, char   ** argv){
  int  fb_fd = 0 ;
  char   * env = " /dev/fb0 " ;
  struct  fb_fix_screeninfo fb_fixinfo;
  struct  fb_var_screeninfo fb_varinfo;
  if ((fb_fd = open(env,O_RDWR)) < 0 ){
  printf( " Error:open FrameBuffer device:%s " n " ,env);
   return   - 1 ;
 } else {
  printf( " OK:open FrameBuffer device:%s " n " ,env);
 }
  if (ioctl(fb_fd,FBIOGET_FSCREENINFO, & fb_fixinfo) ==- 1 ){
  printf( " Error:FBIOGET_FSCREENINFO " n " );
   goto  fail;
 }
 printf( " ioctl FBIOGET_FSCREENINFO ok " n " );
 printf( " id=%s " n " ,fb_fixinfo.id);
 printf( " smem_start=%#x " n " ,fb_fixinfo.smem_start);
 printf( " mem_len=%d " n " ,fb_fixinfo.smem_len);
 printf( " type=%d " n " ,fb_fixinfo.type);
 printf( " type_aux=%d " n " ,fb_fixinfo.type_aux);
 printf( " visual=%d " n " ,fb_fixinfo.visual);
 printf( " xpanstep=%d " n " ,fb_fixinfo.xpanstep);
 printf( " ypanstep=%d " n " ,fb_fixinfo.ypanstep);
 printf( " ywrapstep=%d " n " ,fb_fixinfo.ywrapstep);
 printf( " line_length=%d " n " ,fb_fixinfo.line_length);
 printf( " mmio_start=%#x " n " ,fb_fixinfo.mmio_start);
 printf( " mmio_len=%#x " n " ,fb_fixinfo.mmio_len);
 printf( " accel=%d " n " ,fb_fixinfo.accel);
 printf( " reserved[0]=%d " n " ,fb_fixinfo.reserved[0]);
 printf( " reserved[1]=%d " n " ,fb_fixinfo.reserved[1]);
 printf( " reserved[2]=%d " n " ,fb_fixinfo.reserved[2]);
  if (ioctl(fb_fd,FBIOGET_VSCREENINFO, & fb_varinfo) ==- 1 ){
  printf( " Error:ioctl:FBIOGET_VSCREENINFO " n " );
   goto  fail;
 }
 printf( " ioctl FBIOGET_VSCREENINFO ok " n " );
 printf( " xres=%d " n " ,fb_varinfo.xres);
 printf( " yres=%d " n " ,fb_varinfo.yres);
 printf( " xres_virtual=%d " n " ,fb_varinfo.xres_virtual);
 printf( " yres_virtual=%d " n " ,fb_varinfo.yres_virtual);
 printf( " xoffset=%d " n " ,fb_varinfo.xoffset);
 printf( " yoffset=%d " n " ,fb_varinfo.yoffset);
 printf( " bits_per_pixel=%d " n " ,fb_varinfo.bits_per_pixel);
 printf( " grayscale=%d " n " ,fb_varinfo.grayscale);
 printf( " red=%#x " n " ,fb_varinfo.red);
 printf( " green=%#x " n " ,fb_varinfo.green);
 printf( " blue=%#x " n " ,fb_varinfo.blue);
 printf( " transp=%d " n " ,fb_varinfo.transp);
 printf( " nonstd=%d " n " ,fb_varinfo.nonstd);
 printf( " activate=%d " n " ,fb_varinfo.activate);
 printf( " height=%d " n " ,fb_varinfo.height);
 printf( " width=%d " n " ,fb_varinfo.width);
 printf( " accel_flags=%d " n " ,fb_varinfo.accel_flags);
 printf( " pixclock=%d " n " ,fb_varinfo.pixclock);
 printf( " left_margin=%d " n " ,fb_varinfo.left_margin);
 printf( " right_margin=%d " n " ,fb_varinfo.right_margin);
 printf( " upper_margin=%d " n " ,fb_varinfo.upper_margin);
 printf( " lower_margin=%d " n " ,fb_varinfo.lower_margin);
 printf( " hsync_len=%d " n " ,fb_varinfo.hsync_len);
 printf( " vsync_len=%d " n " ,fb_varinfo.vsync_len);
 printf( " sync=%d " n " ,fb_varinfo.sync);
 printf( " vmode=%d " n " ,fb_varinfo.vmode);
 printf( " rotate=%d " n " ,fb_varinfo.rotate);
 printf( " reserved[0]=%d " n " ,fb_varinfo.reserved[0]);
 printf( " reserved[1]=%d " n " ,fb_varinfo.reserved[1]);
 printf( " reserved[2]=%d " n " ,fb_varinfo.reserved[2]);
 printf( " reserved[3]=%d " n " ,fb_varinfo.reserved[3]);
 printf( " reserved[4]=%d " n " ,fb_varinfo.reserved[4]);
 
 close(fb_fd);
  return   0 ;
fail:
 close(fb_fd);
  return   - 1 ;
}

从输出结果来看xres=800,yres=600,从这里可以看出这个FrameBuffer的最大值为800x600
得到framebuffer的信息后，我们开辟一段内存，然后映射framebuffer的内存,
这样当向这段内存写入信息时，framebuffer中就会写入相同的数据，也就会有数据表示的图像显示在屏幕上。
例：在屏幕上显示一个渐变窗体

#include  < stdio.h >
#include  < unistd.h >
#include  < sys / types.h >
#include  < sys / stat.h >
#include  < fcntl.h >
#include  < linux / fb.h >
#include  < errno.h >
#include  < sys / mman.h >
#include  < stdlib.h >
#include  < string .h >
#include  < sys / ioctl.h >
int  flush_screen( char   * buf, char   * framebuf, int  width, int  height);
int  main( int  argc,  char   * argv[])
{
         int  fb_fd = 0 ;
         struct  fb_fix_screeninfo fb_fixinfo;
         struct  fb_var_screeninfo fb_varinfo;
     char   * fb_addr;
    unsigned  long  fb_size;
     char   * buffer;
     int  i = 0 ;
        if ((fb_fd = open( " /dev/fb0 " , O_RDWR)) < 0 ){
         printf( " open framebuffer device failed. " n " );
          return   - 1 ;
       }
    printf( " open framebuffer device ok " n " );
     
         if (ioctl(fb_fd, FBIOGET_FSCREENINFO,  & fb_fixinfo)  ==   - 1 )
        {
                printf( " ioctl FBIOGET_FSCREENINFO failed. " n " );
                 return   - 1 ;
        }
    printf( " ioctl FBIOGET_FSCREENINFO ok " n " );
         if (ioctl(fb_fd, FBIOGET_VSCREENINFO,  & fb_varinfo)  ==   - 1 )
        {
                printf( " ioctl FBIOGET_VSCREENINFO failed. " n " );
                 return   - 1 ;
        }
    printf( " ioctl FBIOGET_VSCREENINFO ok " n " );
        fb_size  =  fb_varinfo.yres  *  fb_fixinfo.line_length;    // 整个framebuffer的大小
        fb_addr  =  ( char   * )mmap(NULL, fb_size, PROT_READ | PROT_WRITE,MAP_SHARED, fb_fd,  0 );  // 将framebuffer的物理地址映射到进程地址空间
        buffer = ( char * )malloc(fb_varinfo.yres  *  fb_fixinfo.line_length);  // 申请一个缓冲区，采用双缓冲方式
     for (i = 0 ;i <= 0xff ;i += 0x0f ){
          memset(buffer,i,fb_varinfo.yres  *  fb_fixinfo.line_length);
          flush_screen(buffer,fb_addr,fb_varinfo.xres,fb_varinfo.yres);
      sleep( 1 );
    }
         if  ( ! fb_addr)
                exit( 1 );
        free(buffer);
         return   0 ;
}

int  flush_screen( char   * buf, char   * framebuf, int  width, int  height)
{
                 char   * t_data  =  buf;
                 char   * t_fb_addr  =  framebuf;
                 int  bytew =  width << 1 ;
                 while ( -- height  >=   0 )
                {
                        memcpy(t_fb_addr,t_data,bytew);
                        t_fb_addr  +=  width;
                        t_data  +=  width;
                }
}

编译后，运行看一下结果，尽量在字符模式下运行
vi /etc/inittab将运行级别改为3
重启后，运行一下看看结果。

参考链接：
http://www.blogjava.net/lihao336/admin/EditPosts.aspx?postid=345547