/* rotating cube with viewer movement from Chapter 5 */
/* cube definition and display similar to rotating-cube program */

/* we use the Lookat function in the display callback to point the
viewer, whose position can be altered by the x, X, y, Y, z, and Z keys */
/* the perspective view is set in the reshape callback */

#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}};

void polygon(int a, int b, int c , int d)
{
 glBegin(GL_POLYGON);
  glColor3fv(colors[a]);
  glVertex3fv(vertices[a]);
  glVertex3fv(vertices[b]);
  glVertex3fv(vertices[c]);
  glVertex3fv(vertices[d]);
 glEnd();
}

void colorcube()
{
 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);
}

static GLfloat theta[] = {0.0,0.0,0.0};
static GLint axis = 2;
static GLdouble viewer[]= {0.0, 0.0, 5.0}; /* initial viewer location */

void display()
{

 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

/* update viewer position in model-view matrix */

 glLoadIdentity();
 gluLookAt(viewer[0],viewer[1],viewer[2], 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

/* rotate cube */

 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();

 glFlush();
 glutSwapBuffers();
}

void mouse(int btn, int state, int x, int y)
{
 if(btn==GLUT_LEFT_BUTTON && state == GLUT_DOWN) axis = 0;
 if(btn==GLUT_MIDDLE_BUTTON && state == GLUT_DOWN) axis = 1;
 if(btn==GLUT_RIGHT_BUTTON && state == GLUT_DOWN) axis = 2;
 theta[axis] += 2.0;
 if( theta[axis] > 360.0 ) theta[axis] -= 360.0;
 display();
}

void keys(unsigned char key, int x, int y)
{

/* use x, X, y, Y, z, and Z keys to move viewer */

   if(key == 'x') viewer[0]-= 1.0;
   if(key == 'X') viewer[0]+= 1.0;
   if(key == 'y') viewer[1]-= 1.0;
   if(key == 'Y') viewer[1]+= 1.0;
   if(key == 'z') viewer[2]-= 1.0;
   if(key == 'Z') viewer[2]+= 1.0;
   display();
}

void myReshape(int w, int h)
{
 glViewport(0, 0, w, h);

/* use a perspective view */

 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 if(w<=h) glFrustum(-2.0, 2.0, -2.0 * (GLfloat) h/ (GLfloat) w,
       2.0* (GLfloat) h / (GLfloat) w, 2.0, 20.0);
 else glFrustum(-2.0, 2.0, -2.0 * (GLfloat) w/ (GLfloat) h,
       2.0* (GLfloat) w / (GLfloat) h, 2.0, 20.0);

/* or we can use gluPerspective */
/* gluPerspective(45.0, w/h, 1.0, 10.0); */

 glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char **argv)
{
 glutInit(&argc, argv);
 glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
 glutInitWindowSize(500, 500);
 glutCreateWindow("colorcube");
 glutReshapeFunc(myReshape);
 glutDisplayFunc(display);
 glutMouseFunc(mouse);
 glutKeyboardFunc(keys);
 glEnable(GL_DEPTH_TEST);
 glutMainLoop();
}
