write to /dev/fb

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include "graphic.h"
#include "common.h"


static int fbfd = 0;
static struct fb_var_screeninfo vinfo;
static struct fb_fix_screeninfo finfo;
static long int screensize = 0;
static char *fbp = 0;



static void openfb()
{
     fbfd = open("/dev/fb0", O_RDWR);
     if (fbfd == -1) {
         perror("Error: cannot open framebuffer device");
         exit(1);
     }
     printf("The framebuffer device was opened successfully.\n");

     if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {
         perror("Error reading fixed information");
         exit(2);
     }

     if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {
         perror("Error reading variable information");
         exit(3);
     }

     screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

     fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
}


static void closefb(){
     munmap(fbp, screensize);
     close(fbfd);
}


static void clearScreen(){
    for(int i = 0; i<screensize; i++)
    {
        if (vinfo.bits_per_pixel == 32) {
               *(fbp + i) = 0;
        }
    }
}


static void line(int x1, int y1, int x2, int y2) {
    int x_start ,x_end, _y1,_y2, temp ;
    long int location;

    _y1 = min(y1, y2);
    _y2 = max(y1, y2);
    if (_y1 == _y2) _y2++;

    for(int y = _y1; y <= _y2; y++)
    {
        x_start =  (y-_y1) * (x2-x1) / (_y2-_y1) + x1;
        x_end = (y+1-_y1) * (x2-x1) / (_y2-_y1) + x1;

        temp = x_start;
        x_start = min(x_start,x_end);
        x_end = max(temp, x_end);

        for (int x = x_start; x <= x_end; x++)
        {
            location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                       (y+vinfo.yoffset) * finfo.line_length;

            if (vinfo.bits_per_pixel == 32) {
                    //RGBA
                     *(fbp + location) = y;          // B
                     *(fbp + location + 1) = x;      // G
                     *(fbp + location + 2) = 200;    // R
                     *(fbp + location + 3) = 0;      // A
            }
        }
    }
}


int test(const char * file_name) {


     openfb();
     clearScreen();

     line(5,5,80,100);
     line(80,5,5,100);
     line(100,5,140,50);
     line(180,5,100,100);
     line(200,5,200,100);
     line(280,5,200,100);
     line(280,5,280,100);
     line(220,5,250,10);
     closefb();

    return 1;
}