如何使用c语言在framebuffer中绘制图形..？

#include <fcntl.h>
#include<linux/fb.h>
#include <sys/ioctl.h>
#include <sys/mman.h>

int fbfd = open("/dev/fb0", O_RDWR);
if (fbfd == -1) {
    perror("Error: cannot open framebuffer device");
    exit(1);
}

struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;

if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {
    perror("Error reading variable information");
    exit(1);
}

if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {
    perror("Error reading fixed information");
    exit(1);
}

unsigned char *fbp = (unsigned char *)mmap(0, finfo.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
if (fbp == MAP_FAILED) {
    perror("Error: failed to map framebuffer device to memory");
    exit(1);
}

// Draw something here

munmap(fbp, finfo.smem_len);
close(fbfd);