CG 9 - SCAN LINE ALGORITHM

9. Develop a menu driven program to fill the polygon using the Scan line algorithm

#include<stdio.h>
#include<math.h>
#include<iostream>
#include<GL/glut.h>
int le[500], re[500], flag=0 ,m;

void init()
{
gluOrtho2D(0, 500, 0, 500);
}

void edge(int x0, int y0, int x1, int y1)
{
if (y1<y0)
{
int tmp;
tmp = y1;
y1 = y0;
y0 = tmp;
tmp = x1;
x1 = x0;
x0 = tmp;
}
int x = x0;
m = (y1 - y0) / (x1 - x0);
for (int i = y0; i<y1; i++)
{
if (x<le[i])
le[i] = x;
if (x>re[i])
re[i] = x;
x += (1 / m);
}
}

void display()
{
glClearColor(1, 1, 1, 1);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0, 0, 1);
glBegin(GL_LINE_LOOP);
glVertex2f(200, 100);
glVertex2f(100, 200);
glVertex2f(200, 300);
glVertex2f(300, 200);
glEnd();
for (int i = 0; i<500; i++)
{
le[i] = 500;
re[i] = 0;
}
edge(200, 100, 100, 200);
edge(100, 200, 200, 300);
edge(200, 300, 300, 200);
edge(300, 200, 200, 100);
if (flag == 1)
{
for (int i = 0; i < 500; i++)
{
if (le[i] < re[i])
{
for (int j = le[i]; j < re[i]; j++)
{
glColor3f(1, 0, 0);
glBegin(GL_POINTS);
glVertex2f(j, i);
glEnd();
}
}
}
}
glFlush();
}

void ScanMenu(int id)
{
if (id == 1) {
flag = 1;
}
else if (id == 2) {
flag = 0;
}
else { exit(0); }
glutPostRedisplay();
}

int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitWindowPosition(100, 100);
glutInitWindowSize(500, 500);
glutCreateWindow("scan line");
init();
glutDisplayFunc(display);
glutCreateMenu(ScanMenu);
glutAddMenuEntry("scanfill", 1);
glutAddMenuEntry("clear", 2);
glutAddMenuEntry("exit", 3);
glutAttachMenu(GLUT_RIGHT_BUTTON);
glutMainLoop();
return 0;
}

OUTPUT :

( click on image to zoom )