Translation and scaling of polygon using OpenGL

OpenGL_BasicTransformations.cpp

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

int pntX1, pntY1, choice = 0, edges;
vector<int> pntX;
vector<int> pntY;
int transX, transY; 
double scaleX, scaleY;

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

void drawPolygon()
{
	glBegin(GL_POLYGON);
	glColor3f(1.0, 0.0, 0.0);
	for(int i = 0; i < edges; i++)
	{
		glVertex2i(pntX[i], pntY[i]);
	}
	glEnd();
}


void drawPolygonTrans(int x, int y)
{
	glBegin(GL_POLYGON);
	glColor3f(0.0, 1.0, 0.0);
	for(int i = 0; i < edges; i++)
	{
		glVertex2i(pntX[i] + x, pntY[i] + y);
	}
	glEnd();
}

void drawPolygonScale(double x, double y)
{
	glBegin(GL_POLYGON);
	glColor3f(0.0, 0.0, 1.0);
	for(int i = 0; i < edges; i++)
	{
		glVertex2i(round(pntX[i] * x), round(pntY[i] * 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 myDisplay(void)
{
	glClear (GL_COLOR_BUFFER_BIT);
	glColor3f (0.0, 0.0, 0.0);

	if (choice == 1)
	{
		drawPolygon();
		drawPolygonTrans(transX, transY);
	}
	else if (choice == 2)
	{
		drawPolygon();
		drawPolygonScale(scaleX, scaleY);
	}
	
	glFlush ();
}

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

	cout << "1. Translation" << endl;
	cout << "2. Scaling" << endl;
	cout << "3. Exit" << endl;

	cin >> choice;

	if (choice == 3) {
		return;
	}

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

	cout << "Enter no of edges: "; cin >> edges;

	for (int i = 0; i < edges; i++)
	{
		cout << "Enter co-ordinates for vertex  " << i + 1 << " : "; cin >> pntX1 >> pntY1;
		pntX.push_back(pntX1);
		pntY.push_back(pntY1);
	}

	if (choice == 1)
	{
		cout << "Enter the translation factor for X and Y: "; cin >> transX >> transY;
	}
	else if (choice == 2)
	{
		cout << "Enter the scaling factor for X and Y: "; cin >> scaleY >> scaleX;
	}

	//cout << "\n\nPoints:" << pntX[0] << ", " << pntY[0] << endl;



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

}