OpenGL Line Generation Algorithms Implementation

OpenGL_LineAlgo.cpp

#include <stdio.h>
#include <math.h>
#include <iostream>
#include <GL/glut.h>
using namespace std;

int pntX1, pntY1, pntX2, pntY2, choice = 0;
double x, y, length, xinc, yinc;

int round(double d)
{
  return floor(d + 0.5);
}

void plot(int x, int y)
{
	glBegin(GL_POINTS);
	glVertex2i(x, y);
	glEnd();
}


void myInit (void)
{
	glClearColor(1.0, 1.0, 1.0, 0.0);
	glColor3f(0.0f, 0.0f, 0.0f);
	glPointSize(4.0);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0.0, 640.0, 0.0, 480.0);
}



void ddaAlgo()
{
	if (abs(pntY2 - pntY1) > abs(pntX2 - pntX1)) 
	{
		length = abs(pntY2 - pntY1);
	}
	else
	{
		length = abs(pntX2 - pntX1);
	}

	xinc = (pntX2 - pntX1) / length;
	yinc = (pntY2 - pntY1) / length;

	x = pntX1, y = pntY1;

	for(int i = 0; i < length; i++)
	{
		plot(round(x), round(y));
		x += xinc;
		y += yinc;
	}
}

void bresenhamAlgo()
{
	int dx = (pntX2 - pntX1),
		dy = (pntY2 - pntY1);
	int d = 2 * dy - dx;
	int incrE = 2 * dy;
	int incrNE = 2 * (dy - dx);
	
	int x = pntX1; y = pntY1;

	while (x < pntX2)
	{
		if (x % 5 == 0)
		{
			goto pass;
		}
		plot(x, y);

	pass:
		if (d <= 0)
		{
			d += incrE;
		}
		else
		{
			d+= incrNE;
			y++;
		}
		x++;

	}
}

void drawLineAlg (void)
{
	if (choice == 1)
	{
		ddaAlgo();
	}
	else if (choice == 2)
	{
		bresenhamAlgo();
	}
	else 
	{
		cout << "Error: Invalid choice." << endl;
	}
}

void drawLine()
{
	glBegin(GL_LINES);
	glVertex2i(pntX1, pntY1+30);
	glVertex2i(pntX2, pntY2+30);
	glEnd();
}

void myDisplay(void)
{
	glClear (GL_COLOR_BUFFER_BIT);
	glColor3f (0.0, 0.0, 0.0);
	glPointSize(1.0);
	drawLineAlg();
	drawLine();
	glFlush ();
}

void main(int argc, char** argv)
{	
	cout << "Enter your choice:\n\n" << endl;

	cout << "1. DDA Algorithm" << endl;
	cout << "2. Bresenham" << endl;
	cout << "3. Exit" << endl;

	cin >> choice;

	if (choice == 3) {
		return;
	}

	cout << "\n\nFor Line:\n" << endl;

	cout << "Enter an Initial Point: "; cin >> pntX1; cin >> pntY1;
	cout << "\nEnter the Final Point: "; cin >> pntX2; cin >> pntY2;

	//cout << "\n\nPoints:" << pntX1 << ", " << pntY1 << ", " << pntX2 << ", " << pntY2 << endl;

	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
	glutInitWindowSize (640, 480);
	glutInitWindowPosition (100, 150);
	glutCreateWindow ("Line Drawing Alogrithms");
	glutDisplayFunc(myDisplay);
	myInit ();
	glutMainLoop();

}