/* matrix4.c
 *
 * An example showing matrix maniuplation in OpenGL.
 * Ray S. Babcock, September 23, 1996, Montana State University
 *           revised September 22, 1998 for Vertex Arrays
 *
 * OpenGL(TM) is a trademark of Silicon Graphics, Inc.
 *
 *  This program draws three axes and three planes
 *  with matrix push and pop operations.
 *  This program animates a "fly-around"
 *  of the camera.
 */

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

#define DELTA_RAD 0.005
#define TWO_PI 2*M_PI

static double rad=0.0,
       x=0.0,
       z=0.0;


void
fly_around()
{
    rad += DELTA_RAD;
    if(rad >= TWO_PI) rad=0.0;
    z = cos(rad);
    x = sin(rad);
    glutPostRedisplay();
}

void
axes (double r, double g, double b, GLubyte ax[])
{
GLfloat axes_vertices[] = {0.0, 0.0, 0.0,
		           1.0, 0.0, 0.0,
			   0.0, 1.0, 0.0,
			   0.0, 0.0, 1.0};

GLfloat max=1.0;
  
  glColor3f(r,g,b);
  glVertexPointer(3, GL_FLOAT, 0, axes_vertices);
  glDrawElements(GL_LINES, 6, GL_UNSIGNED_BYTE, ax);
   /* draw a letter X */
  glBegin(GL_LINES);
    glVertex3f(max, 0.05, 0.0);
    glVertex3f(max+0.05, -0.05, 0.0);
    glVertex3f(max+0.05, 0.05, 0.0);
    glVertex3f(max, -0.05, 0.0);
  glEnd();
   /* draw a letter Y */
  glBegin(GL_LINES);
    glVertex3f(-0.025, max+0.05, 0.0);
    glVertex3f(0.0, max+0.025, 0.0);
    glVertex3f(0.0, max+0.025, 0.0);
    glVertex3f(0.025, max+0.05, 0.0);
    glVertex3f(0.0, max+0.025, 0.0);
    glVertex3f(0.0, max+0.005, 0.0);
  glEnd();
   /* draw a letter Z */
  glBegin(GL_LINES);
    glVertex3f(-0.025, 0.025, max+.005);
    glVertex3f(0.025, 0.025, max+0.005);
    glVertex3f(0.025, 0.025, max+0.005);
    glVertex3f(-0.025, -0.025, max+0.005);
    glVertex3f(-0.025, -0.025, max+0.005);
    glVertex3f(0.025, -0.025, max+0.005);
  glEnd();
}

void
plane(double r, double g, double b)
{
GLfloat plane_vertices[] = {-0.5, -0.5, -0.01,
	      		      0.5, -0.5, -0.01,
			      0.5, 0.5, -0.01,
			      -0.5, 0.5, -0.01};

GLubyte plane_indices[] = {0, 1, 2, 3};

   glColor3f(r,g,b);
   glVertexPointer(3, GL_FLOAT, 0, plane_vertices);
   glDrawElements(GL_POLYGON, 4, GL_UNSIGNED_BYTE, plane_indices);
}

void init(void)
{
   glClearColor (0.6, 0.6, 0.6, 0.6);
   glShadeModel(GL_FLAT);
   glEnable(GL_DEPTH_TEST);
   glEnableClientState(GL_VERTEX_ARRAY);

   glMatrixMode (GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(40.0, 1.0, 1.0, 100.0);
   glMatrixMode (GL_MODELVIEW);
   glLoadIdentity();
   gluLookAt (0.0, 2.0, 5.0, 0.0,  0.0, 0.5, 0.0, 1.0, 0.0);

}

void
draw_scene()
{
GLubyte axes_indices[] = {0,1,0,2,0,3};


   glLoadIdentity();
   gluLookAt (x*5.0, 2.0, z*5.0, 0.0, 0.5, 0.0, 0.0, 1.0, 0.0);
   axes(1.0, 1.0, 1.0, axes_indices);

   glPushMatrix();
   glTranslatef(0.0, 1.0, 0.6);
     axes(1.0, 1.0, 0.0, axes_indices);
     plane(1.0,0.0,0.0);
   glPopMatrix();
   glPushMatrix();
   glRotatef(90.0, 0.0, 1.0, 0.0);  
   glTranslatef(0.0, 1.0, 0.6);    
     axes(1.0, 0.0, 1.0, axes_indices);
     plane(0.0,1.0,0.0);
   glPopMatrix();
   glPushMatrix();
   glRotatef(180.0, 1.0, 0.0, 0.0); 
   glTranslatef(0.0, 0.0, 0.6);   
     axes(0.0, 1.0, 1.0, axes_indices);
     plane(0.0,0.0,1.0);
   glPopMatrix();
   glFlush();
}

void
display()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    draw_scene();
    glFlush();
    glutSwapBuffers();
}

void reshape (int w, int h)
{
   glViewport (0, 0, (GLsizei) w, (GLsizei) h);
}

/* ARGSUSED1 */
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_DOUBLE | GLUT_RGB);
   glutInitWindowSize (340, 340);
   glutInitWindowPosition (0, 0);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutIdleFunc(fly_around);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}