/* Rotating cube with color interpolation */

/* Demonstration of use of homogeneous coordinate 
transformations and simple data structure for representing
a cube. */

/* Colors are assigned to the vertices. */
/*Cube is centered at the origin. */


/* Un-comment the following to enable depth buffering */
#define DEPTH

#define ESC 0x1b

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


GLfloat vertices[][3] = {{-1.0,-1.0,-1.0},{1.0,-1.0,-1.0},
{1.0,1.0,-1.0}, {-1.0,1.0,-1.0}, {-1.0,-1.0,1.0}, 
{1.0,-1.0,1.0}, {1.0,1.0,1.0}, {-1.0,1.0,1.0}};

GLfloat colors[][3] = {{0.0,0.0,0.0},{1.0,0.0,0.0},
{1.0,1.0,0.0}, {0.0,1.0,0.0}, {0.0,0.0,1.0}, 
{1.0,0.0,1.0}, {1.0,1.0,1.0}, {0.0,1.0,1.0}};

static GLfloat theta[] = {0.0,0.0,0.0};   /* x, y, z rotations. */
static GLint axis = 1;                    /* Select y axis for
                                           * rotation. */


void polygon(int a, int b, int c , int d)
{

/* draw a polygon via list of vertices */

   glBegin(GL_POLYGON);
      glColor3fv(colors[a]);
      glVertex3fv(vertices[a]);
      glColor3fv(colors[b]);
      glVertex3fv(vertices[b]);
      glColor3fv(colors[c]);
      glVertex3fv(vertices[c]);
      glColor3fv(colors[d]);
      glVertex3fv(vertices[d]);
   glEnd();
}

void colorcube(void)
{

/* map vertices to faces */

   polygon(0,3,2,1);
   polygon(2,3,7,6);
   polygon(0,4,7,3);
   polygon(1,2,6,5);
   polygon(4,5,6,7);
   polygon(0,1,5,4);
}


void display(void)
{
/* display callback, clear frame buffer and z buffer,
   rotate cube and draw, swap buffers */


#ifdef DEPTH
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
#else
   glClear(GL_COLOR_BUFFER_BIT);
#endif
   glLoadIdentity();
   glRotatef(theta[0], 1.0, 0.0, 0.0);
   glRotatef(theta[1], 0.0, 1.0, 0.0);
   glRotatef(theta[2], 0.0, 0.0, 1.0);

   colorcube();

   glutSwapBuffers();
}


void spinCube(void)
{

/* Idle callback, spin cube 2 degrees about selected axis */

   theta[axis] += 1.0;
   if( theta[axis] > 360.0 ) theta[axis] -= 360.0;
   display();
}


void keyboard(unsigned char key, int x, int y)
{
   switch (key)
   {
   case 'x':
   case 'X':
      axis = 0;
      break;

   case 'y':
   case 'Y':
      axis = 1;
      break;

   case 'z':
   case 'Z':
      axis = 2;
      break;

   case ESC:
      exit(0);
      break;
   }
}


void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
        glOrtho(-2.0, 2.0, -2.0 * (GLfloat) h / (GLfloat) w,
            2.0 * (GLfloat) h / (GLfloat) w, -2.0, 2.0);
    else
        glOrtho(-2.0 * (GLfloat) w / (GLfloat) h,
            2.0 * (GLfloat) w / (GLfloat) h, -2.0, 2.0, -2.0, 2.0);
    glMatrixMode(GL_MODELVIEW);
}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);

/* need both double buffering and z buffer */

#ifdef DEPTH
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
#else
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
#endif
    glutInitWindowSize(500, 500);
    glutCreateWindow("colorcube");
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
   glutIdleFunc(spinCube);
   glutKeyboardFunc(keyboard);
#ifdef DEPTH
   glEnable(GL_DEPTH_TEST); /* Enable hidden--surface--removal */
#endif
    glutMainLoop();

    return 0;
}