如何编程来使乌班图里面的lcd显示屏画出一个圆，用C语言代码

可以使用以下代码来在乌班图中的lcd显示屏上画出一个圆：

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

#define PI 3.14159265358979323846

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 radius = 50; // 圆的半径
    int center_x = 100; // 圆心的横坐标
    int center_y = 100; // 圆心的纵坐标

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

    // 获取固定屏幕信息
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {
        perror("Error reading fixed information");
        exit(2);
    }

    // 获取可变屏幕信息
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {
        perror("Error reading variable information");
        exit(3);
    }

    // 计算屏幕大小
    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

    // 映射framebuffer到内存中
    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
    if ((int)fbp == -1) {
        perror("Error: failed to map framebuffer device to memory");
        exit(4);
    }

    // 画圆
    for (y = center_y - radius; y < center_y + radius; y++) {
        for (x = center_x - radius; x < center_x + radius; x++) {
            if ((x - center_x) * (x - center_x) + (y - center_y) * (y - center_y) <= radius * radius) {
                location = (x + vinfo.xoffset) * (vinfo.bits_per_pixel / 8) +
                           (y + vinfo.yoffset) * finfo.line_length;
                *(fbp + location) = 255; // 蓝色
                *(fbp + location + 1) = 0; // 绿色
                *(fbp + location + 2) = 0; // 红色
                *(fbp + location + 3) = 0; // 透明度
            }
        }
    }

    munmap(fbp, screensize);
    close(fbfd);

    return 0;
}