/*
 *  cube.c
 *  This program demonstrates a single modeling transformation,
 *  glScalef() and a single viewing transformation, gluLookAt().
 *  A wireframe cube is rendered.
 */
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>

void init(void) 
{
   glClearColor (0.0, 0.0, 0.0, 0.0);
   glShadeModel (GL_FLAT);
}

void display(void)
{
   GLfloat m[16],a;
   int i,j;

   glClear (GL_COLOR_BUFFER_BIT);
   glColor3f (1.0, 1.0, 1.0);
   glLoadIdentity ();             /* clear the matrix */
           /* viewing transformation  */
   //gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
   // rotate 45 degrees 
   // gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 1.0, 1.0, 0.0);
   gluLookAt (0.0, 0.0, 5.0, 0.0, 5.0, 0.0, 0.0, 1.0, 0.0);
   // world rotates by -45 degrees about x
   // and moves by 5 = sqrt(a^2+a^2)   where a=3.535534... rotated
   // z units == -a z-units and -a y units
   glGetFloatv(GL_MODELVIEW_MATRIX,m);
    printf("LookAt\n");
   for (i=0; i<4; i++) {
       for (j=0; j<4; j++) {
	    printf("%f ", m[j*4+i]);
       }
	printf("\n");
   }
   printf("\n");
   // undo the transformation
   glRotatef(45.0,1.0,0,0);
   a = sqrt(25.0/2);
   glTranslatef(0.0, a, a);
   glGetFloatv(GL_MODELVIEW_MATRIX,m);
   for (i=0; i<4; i++) {
       for (j=0; j<4; j++) {
	    printf("%f ", m[j*4+i]);
       }
	printf("\n");
   }
   gluLookAt (0.0, 0.0, 5.0, 0.0, 5.0, 0.0, 0.0, 1.0, 0.0);
   glScalef (1.0, 2.0, 1.0);      /* modeling transformation */ 
   glutWireCube (1.0);
   glFlush ();
}

void reshape (int w, int h)
{
   glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ();
   glFrustum (-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
   glMatrixMode (GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}