// Modified from one of the GLUT sample files by Mark Kilgard simple.c
// uses default viewing volume from (-1, -1, -1) to (1, 1, 1)
// uses orthographic projection

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

// global variables
int npts;

void display(void)
{
	int i, j;
	double x, y;

	glClearColor(0.0, 0.0, 0.0, 0.0);
	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_POINTS);
	// this is where the calculation and drawing take place
		for (j=0; j<npts; j++)
			for (i=0; i<npts; i++)
			{
			// do calculations
				y = -1.0+2.0*j/npts;
				x = -1.0+2.0*i/npts;
			// set color based on calculations
				if ((x>0.0) && (y>0.0))
					glColor3f(0.0, 1.0, 1.0);
				else if ((x<0.0) && (y>0.0))
					glColor3f(1.0, 1.0, 0.0);
				else if ((x<0.0) && (y<0.0))
					glColor3f(1.0, 0.0, 1.0);
				else
					glColor3f(0.5, 0.7, 0.7);
			// draw point
				glVertex2f(x,y);
		}
	glEnd();
	glFlush();
}

int main(int argc, char **argv)
{
	glutInit(&argc, argv);
	glutCreateWindow("triangle");
	glutDisplayFunc(display);
	cout << "How many points along each axis??";
	cin >> npts;
	glutMainLoop();
	return 0;
}