#include <stdlib.h>
#include <GL/glut.h>

/* Minimum stack space */
static USED const char *stack = "$STACK:65535";

void myinit(void)
{
	glDepthFunc(GL_LESS);
	glEnable(GL_DEPTH_TEST);
	glShadeModel(GL_FLAT);
}

void drawPlane(void)
{
	glBegin (GL_QUADS);
		glNormal3f (0.0, 0.0, 1.0);
		glVertex3f (-1.0, -1.0, 0.0);
		glVertex3f (0.0, -1.0, 0.0);
		glVertex3f (0.0, 0.0, 0.0);
		glVertex3f (-1.0, 0.0, 0.0);

		glNormal3f (0.0, 0.0, 1.0);
		glVertex3f (0.0, -1.0, 0.0);
		glVertex3f (1.0, -1.0, 0.0);
		glVertex3f (1.0, 0.0, 0.0);
		glVertex3f (0.0, 0.0, 0.0);

		glNormal3f (0.0, 0.0, 1.0);
		glVertex3f (0.0, 0.0, 0.0);
		glVertex3f (1.0, 0.0, 0.0);
		glVertex3f (1.0, 1.0, 0.0);
		glVertex3f (0.0, 1.0, 0.0);

		glNormal3f (0.0, 0.0, 1.0);
		glVertex3f (0.0, 0.0, 0.0);
		glVertex3f (0.0, 1.0, 0.0);
		glVertex3f (-1.0, 1.0, 0.0);
		glVertex3f (-1.0, 0.0, 0.0);
	glEnd();
}

void display (void)
{
	glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glPushMatrix ();
	glTranslatef (-2.1, 0.0, 0.0);
	glColor3f(1.0, 0.0, 0.0);
	drawPlane ();
	glPopMatrix ();

	glPushAttrib(GL_CURRENT_BIT);

	glPushMatrix ();
	glColor3f(0.0, 1.0, 0.0);
	glTranslatef (0.0, 0.0, 0.0);
	drawPlane ();
	glPopMatrix ();

	glPopAttrib();

	glPushMatrix ();
	glTranslatef (2.1, 0.0, 0.0);
	drawPlane ();
	glPopMatrix ();

	glFlush ();
}

void myReshape(int w, int h)
{
	glViewport (0, 0, w, h);
	glMatrixMode (GL_PROJECTION);
	glLoadIdentity ();
	if (w <= h) {
		glOrtho (-1.5, 1.5, -1.5*(GLdouble)h/(GLdouble)w,
			1.5*(GLdouble)h/(GLdouble)w, -10.0, 10.0);
	}
	else {
		glOrtho (-1.5*(GLdouble)w/(GLdouble)h,
			1.5*(GLdouble)w/(GLdouble)h, -1.5, 1.5, -10.0, 10.0);
	}
	glMatrixMode (GL_MODELVIEW);
}

static void key(unsigned char k, int x, int y)
{
	switch (k) {
		case 27:  /* Escape */
			exit(0);
			break;
		default:
			return;
	}
	glutPostRedisplay();
}

/*  Main Loop
 *  Open window with initial window size, title bar,
 *  RGBA display mode, and handle input events.
 */
int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowSize (500, 200);
	glutCreateWindow (argv[0]);
	myinit();
	glutReshapeFunc (myReshape);
	glutDisplayFunc(display);
	glutKeyboardFunc(key);
	glutMainLoop();
	return 0;             /* ANSI C requires main to return int. */
}