framebuffer操作初识

#include <unistd.h>#include <stdio.h>#include <fcntl.h>#include <linux/fb.h>#include <sys/mman.h>#include <stdlib.h>#include <sys/ioctl.h>#include <string.h>#define FrameBufferDriverName "/dev/fb0" void fb_memclear (void *addr, int c, size_t len) {     memset(addr, c, len); } int main () { int fp=0; struct fb_var_screeninfo vinfo; struct fb_fix_screeninfo finfo; long screensize1,screensize2; char* fbp = 0; int index = 0; fp = open (FrameBufferDriverName,O_RDWR); if (fp < 0) {printf("Error : Can not open framebuffer device/n");exit(1); } if (ioctl(fp,FBIOGET_FSCREENINFO,&finfo)) {  printf("Error reading fixed information/n");  exit(2); }  if (ioctl(fp,FBIOGET_VSCREENINFO,&vinfo)) {  printf("Error reading variable information/n");  exit(3); }screensize2 = vinfo.yres_virtual * finfo.line_length;screensize1 = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8; /*字节数*//*这就是把fp所指的文件中从开始到screensize大小的内容给映射出来，得到一个指向这块空间的指针*/fbp =(char *) mmap (0, finfo.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fp,0);if ((long int)fbp == -1)     {        printf ("Error: failed to map framebuffer device to memory./n");        exit (4);     } while(1) {  sleep(1); if(index > 65535){ index == 0; } /* printf("vinfo.xres value is %d\n",vinfo.xres); printf("vinfo.yres value is %d\n",vinfo.yres); printf("finfo.line_length value is %d\n",finfo.line_length); printf("vinfo.bits_per_pixel value is %d\n",vinfo.bits_per_pixel); printf("vinfo.yres_virtual value is %d\n",vinfo.yres_virtual); printf("screensize1 value is %d\n",screensize1); printf("screensize2 value is %d\n",screensize2); printf("finfo.smem_len value is %d\n",finfo.smem_len); printf("index value is %d\n",index);*/ //showImage(fbp,vinfo.xres,vinfo.yres,vinfo.bits_per_pixel); fb_memclear((void *)fbp,index,finfo.smem_len); index += 50; }munmap ((void *)fbp,finfo.smem_len); /*解除映射*/close (fp);    /*关闭文件*/return 0;  }

    附上操作fb的两个主要结构体成员：（详情见<linux/fb.h>）

#if 0struct fb_fix_screeninfo {char id[16]; /* identification string eg "TT Builtin" */IDunsigned long smem_start; /* Start of frame buffer mem */ 内存起始/* (physical address) */ 物理地址__u32 smem_len; /* Length of frame buffer mem */ 内存大小__u32 type; /* see FB_TYPE_* */ __u32 type_aux; /* Interleave for interleaved Planes */插入区域__u32 visual; /* see FB_VISUAL_* */__u16 xpanstep; /* zero if no hardware panning */没有硬件设备就为零__u16 ypanstep; /* zero if no hardware panning */__u16 ywrapstep; /* zero if no hardware ywrap */__u32 line_length; /* length of a line in bytes */ 一行的字节表示unsigned long mmio_start; /* Start of Memory Mapped I/O */内存映射的I/O起始/* (physical address) */ __u32 mmio_len; /* Length of Memory Mapped I/O */ I/O的大小__u32 accel; /* Type of acceleration available */ 可用的加速类型__u16 reserved[3]; /* Reserved for future compatibility */};struct fb_var_screeninfo{__u32 xres; /* visible resolution */   //可视区域__u32 yres;__u32 xres_virtual; /* virtual resolution */  //可视区域__u32 yres_virtual;__u32 xoffset; /* offset from virtual to visible resolution */ //可视区域的偏移__u32 yoffset;__u32 bits_per_pixel; /* guess what */  //每一象素的bit数__u32 grayscale; /* != 0 Gray levels instead of colors *///等于零就成黑白struct fb_bitfield red; /* bitfield in fb mem if true color, */真彩的bit机构struct fb_bitfield green; /* else only length is significant */struct fb_bitfield blue;   struct fb_bitfield transp; /* transparency */  透明__u32 nonstd; /* != 0 Non standard pixel format */ 不是标准格式__u32 activate; /* see FB_ACTIVATE_* */__u32 height; /* height of picture in mm */ 内存中的图像高度__u32 width; /* width of picture in mm */ 内存中的图像宽度__u32 accel_flags; /* acceleration flags (hints) */ 加速标志/* Timing: All values in pixclocks, except pixclock (of course) */时序-_-这些部分就是显示器的显示方法了，可以找相关的资料看看__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 */  水平可视区域__u32 vsync_len; /* length of vertical sync */   垂直可视区域__u32 sync; /* see FB_SYNC_* */__u32 vmode; /* see FB_VMODE_* */__u32 reserved[6]; /* Reserved for future compatibility */ 备用－以后开发};#endif