应用多元统计pdf:framebuffer应用程序编写

 

1. 了解linux/fb.h中的关于framebuffer的结构体 fb_fix_screeninfo和fb_var_screeninfo中的内容。（红色的是编程经常要用到的）。   struct fb_fix_screeninfo {   //存放于设备无关的常值信息，如显存大小等。
char id[16];    /* identification string eg "TT Builtin" */
    unsigned long smem_start; /* Start of frame buffer mem 显存起始地址*/
      /* (physical address) */
    __u32 smem_len;    /* Length of frame buffer mem 显存大小*/
    __u32 type;    /* see FB_TYPE_*   */
    __u32 type_aux;    /* Interleave for interleaved Planes */
    __u32 visual;    /* see FB_VISUAL_*   */
    __u16 xpanstep;    /* zero if no hardware panning */
__u16 ypanstep;    /* zero if no hardware panning */
    __u16 ywrapstep;   /* zero if no hardware ywrap    */
    __u32 line_length;   /* length of a line in bytes  每一行字节数 */
    unsigned long mmio_start; /* Start of Memory Mapped I/O   */
      /* (physical address) */
    __u32 mmio_len;    /* Length of Memory Mapped I/O */
   __u32 accel;    /* Indicate to driver which */
      /* specific chip/card we have */
   __u16 reserved[3];   /* Reserved for future compatibility */
};struct fb_var_screeninfo {   //存放于设备无关的数据信息，如分辨率等。
u32 xres;    /* visible resolution   每一行的点数*/
__u32 yres;   /*每一列的点数*/
__u32 xres_virtual;   /* virtual resolution   */
__u32 yres_virtual;
__u32 xoffset;    /* offset from virtual to visible起始行偏移 */
__u32 yoffset;    /* resolution  起始列偏移 */__u32 bits_per_pixel;   /* guess what   每一点的位数*/
__u32 grayscale;   /* != 0 Graylevels instead of colors */struct fb_bitfield red;   /* bitfield in fb mem if true color, */
struct fb_bitfield green; /* else only length is significant */
struct fb_bitfield blue;
struct fb_bitfield transp; /* transparency    */ __u32 nonstd;    /* != 0 Non standard pixel format */__u32 activate;    /* see FB_ACTIVATE_*   */__u32 height;    /* height of picture in mm    */
__u32 width;    /* width of picture in mm     */__u32 accel_flags;   /* (OBSOLETE) see fb_info.flags *//* Timing: All values in pixclocks, except pixclock (of course) */
__u32 pixclock;    /* pixel clock in ps (pico seconds) */
__u32 left_margin;   /* time from sync to picture */
__u32 right_margin;   /* time from picture to sync */
__u32 upper_margin;   /* time from sync to picture */
__u32 lower_margin;
__u32 hsync_len;   /* length of horizontal sync */
__u32 vsync_len;   /* length of vertical sync */
__u32 sync;    /* see FB_SYNC_*   */
__u32 vmode;    /* see FB_VMODE_*   */
__u32 rotate;    /* angle we rotate counter clockwise */
__u32 reserved[5];   /* Reserved for future compatibility */
};显存大小计算：xres * yres * bits_per_pixel/8 (BYTES)2.编程流程：（1） 打开设备 open("/dev/fb0",O_RDWR);(2)   获取framebuffer设备信息.ioctl(int fb,FBIOGET_FSCREENINFO,&finfo);       ioctl函数是实现对设备的信息获取和设定，第一个参数为文件描述符，第二个参数为具体设备的参数，对于framebuffer,参数在linux/fb.h中定义的。      #define FBIOGET_VSCREENINFO 0x4600   //获取设备无关的数据信息fb_var_screeninfo
      #define FBIOPUT_VSCREENINFO 0x4601   //设定设备无关的数据信息
      #define FBIOGET_FSCREENINFO 0x4602   //获取设备无关的常值信息fb_fix_screeninfo
      #define FBIOGETCMAP   0x4604        //获取设备无关颜色表信息
      #define FBIOPUTCMAP   0x4605       //设定设备无关颜色表信息
      #define FBIOPAN_DISPLAY   0x4606
      #define FBIO_CURSOR            _IOWR('F', 0x08, struct fb_cursor)      第三个参数是存放信息的结构体或者缓冲区(3)内存映射 mmap函数。头文件：sys/mman.h .常用用法：mmap(0,screensize,PROT_RD　｜PROT_WR,MAP_SHARED,int fb,0)返回映射的首地址。3。实例程序实现在lcd 上全屏写 blue 色#include
#include
#include
#include
#include
#include int main()
{
        int fbfd = 0;
        struct fb_var_screeninfo vinfo;
        struct fb_fix_screeninfo finfo;
        long int screensize = 0;
        char *fbp = 0;
        int x = 0, y = 0;
        long int location = 0;
       int sav=0;

        /* open device*/
        fbfd = open("/dev/fb0", O_RDWR);
        if (!fbfd) {
                printf("Error: cannot open framebuffer device.\n");
                exit(1);
        }
        printf("The framebuffer device was opened successfully.\n");               /* Get fixed screen information */
        if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
                printf("Error reading fixed information.\n");
                exit(2);
        }        /* Get variable screen information */
        if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
                printf("Error reading variable information.\n");
                exit(3);
        }/* show these information*/
printf("vinfo.xres=%d\n",vinfo.xres);
printf("vinfo.yres=%d\n",vinfo.yres);
printf("vinfo.bits_per_bits=%d\n",vinfo.bits_per_pixel);
printf("vinfo.xoffset=%d\n",vinfo.xoffset);
printf("vinfo.yoffset=%d\n",vinfo.yoffset);
printf("finfo.line_length=%d\n",finfo.line_length);
        /* Figure out the size of the screen in bytes */
        screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
       
        /* Map the device to memory */
        fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,                fbfd, 0);      
        if ((int)fbp == -1) { printf("Error: failed to map framebuffer device to memory.\n"); exit(4);
        }
        printf("The framebuffer device was mapped to memory successfully.\n");memset(fbp,0,screensize);
            /* Where we are going to put the pixel */

for(x=0;xfor(y=0;y
location = (x vinfo.xoffset) * (vinfo.bits_per_pixel/8)
         (y vinfo.yoffset) * finfo.line_length;        *(fbp location) = 0xff; /* blue */
        *(fbp location 1) = 0x00;     
          }            
      munmap(fbp, screensize); /* release the memory */
      close(fbfd);
      return 0;
}这是最简单的直接写framebuffer 的程序，也是我在这一方面编程的起步。希望在以后的学习中能够和朋友们一起提高