C Program to fill any given polygon using scan-line area filling algorithm

#include <graphics.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
 
struct Node
{
int x;
int y;
struct Node* next;
};
 
void fill (int pt[][2], int clr);
void floodfill4 (int x, int y, int oldclr, int newclr);
void insert (int x, int y, struct Node** last);
 
void main()
{
int i, j;
int pt[3][2];
int clr;
 
printf ("This program demonstrates filling a polygon.\n");
printf ("Enter the x- and y-coordinates for three points:\n");
for (i=0; i<3; i++)
for (j=0; j<2; j++)
scanf ("%d", &pt[i][j]);
 
printf ("Enter the fill-colour: (Any number from 1 to 14) ");
scanf ("%d", &clr);
fill (pt, clr);
}
 
void fill (int pt[][2], int clr)
{
int gd = DETECT, gm;
int seedx, seedy;
 
initgraph (&gd, &gm, "..\\bgi");
 
setcolor (WHITE);
line (pt[0][0], pt[0][1], pt[1][0], pt[1][1]);
line (pt[1][0], pt[1][1], pt[2][0], pt[2][1]);
line (pt[2][0], pt[2][1], pt[0][0], pt[0][1]);
getch();
 
seedx = (pt[0][0] + pt[1][0] + pt[2][0]) / 3;
seedy = (pt[0][1] + pt[1][1] + pt[2][1]) / 3;
 
floodfill4 (seedx, seedy, BLACK, clr);
getch();
 
closegraph();
return;
}
 
void floodfill4 (int x, int y, int oldclr, int newclr)
{
struct Node* first, *last, *tmp;
 
first = (struct Node*) malloc (sizeof (struct Node));
if (first == NULL)
{
closegraph();
fprintf (stderr, "floodfill4: Out of memory.\n");
exit (2);
}
if (oldclr == newclr)
{
free (first);
return;
}
 
first->x = x;
first->y = y;
first->next = NULL;
last = first;
 
while (first != NULL)
{
putpixel (x, y, newclr);
 
if (getpixel (x, y-1) == oldclr)
{
putpixel (x, y-1, newclr);
insert (x, y-1, &last);
}
 
 
if (getpixel (x, y+1) == oldclr)
{
putpixel (x, y+1, newclr);
insert (x, y+1, &last);
}
 
if (getpixel (x-1, y) == oldclr)
{
putpixel (x-1, y, newclr);
insert (x-1, y, &last);
}
 
if (getpixel (x+1, y) == oldclr)
{
putpixel (x+1, y, newclr);
insert (x+1, y, &last);
}
 
tmp = first;
first = first->next;
x = first->x;
y = first->y;
free (tmp);
}
}
 
void insert (int x, int y, struct Node** last)
{
struct Node* p;
p = (struct Node*) malloc (sizeof (struct Node));
if (p == NULL)
{
closegraph();
fprintf (stderr, "\n insert: Out of memory.\n");
exit (2);
}
 
p->x = x;
p->y = y;
p->next = NULL;
(*last)->next = p;
*last = (*last)->next;
}