////////////////////////////////////////////////////////////////////////////////////////         
// sphereInBox2.cpp
//
// This program builds on sphereInBox1.cpp. The normals at the vertices of the 
// box can now be drawn in two different ways: as averages of the adjacent face normals
// as in sphereInBox1.cpp, or as perpendiculars to the faces themselves. The box can
// now be rotated.
//
// Interaction:
// Press up/down arrow keys to open/close the box.
// Press space to toggle between averaged and unaveraged normals.
//
// Sumanta Guha.
////////////////////////////////////////////////////////////////////////////////////////

#include <iostream>

#ifdef __APPLE__
#  include <GLUT/glut.h>
#else
#  include <GL/glut.h>
#endif

#define ONE_BY_ROOT_THREE 0.57735

using namespace std;

// Begin globals.
static unsigned int aSide; // List index.
static int step = 0; // Steps in open/closing box lid.
static int averagedNormals = 1; // Whether averaged or unaveraged normals.
static long font = (long)GLUT_BITMAP_8_BY_13; // Font selection.

// Box vertex co-ordinate vectors. 
static float vertices[] = 
{
	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
};

// Vertex indices of each box side, 6 groups of 4.
static unsigned char quadIndices[] = 
{
    3, 2, 1, 0, 
    7, 6, 2, 3,
    4, 5, 6, 7,
	0, 1, 5, 4,
	4, 7, 3, 0,
	6, 5, 1, 2
};

// Box vertex normal vectors = normalized unit vector pointing from origin to vertex.
static float normals[] = 
{
	ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, 
	ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, 
	ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, 
	ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, 
	-ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, 
	-ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, 
	-ONE_BY_ROOT_THREE, ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, 
	-ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE, -ONE_BY_ROOT_THREE
};
// End globals.

// Routine to draw a bitmap character string.
void writeBitmapString(void *font, char *string)
{  
   char *c;

   for (c = string; *c != '\0'; c++) glutBitmapCharacter(font, *c);
}

// Initialization routine.
void setup(void)
{
   aSide = glGenLists (1); // Return a list index.

   // A side of the box in a display list.
   glNewList(aSide, GL_COMPILE);
   glBegin(GL_QUADS);
      glNormal3f(0.0, -1.0, 0.0);
      glVertex3f(1.0, -1.0, 1.0);
	  glVertex3f(-1.0, -1.0, 1.0);
	  glVertex3f(-1.0, -1.0, -1.0);
	  glVertex3f(1.0, -1.0, -1.0);
   glEnd();
   glEndList();

   glClearColor(1.0, 1.0, 1.0, 0.0);
   glEnable(GL_DEPTH_TEST); // Enable depth testing.

   // Turn on OpenGL lighting.
   glEnable(GL_LIGHTING);

   // Light property vectors.
   float lightAmb[] = { 0.0, 0.0, 0.0, 1.0 };
   float lightDifAndSpec[] = { 1.0, 1.0, 1.0, 1.0 };
   float lightPos[] = { 0.0, 1.5, 3.0, 1.0 };
   float globAmb[] = { 0.2, 0.2, 0.2, 1.0 };

   // Light properties.
   glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmb);
   glLightfv(GL_LIGHT0, GL_DIFFUSE, lightDifAndSpec);
   glLightfv(GL_LIGHT0, GL_SPECULAR, lightDifAndSpec);
   glLightfv(GL_LIGHT0, GL_POSITION, lightPos);

   glEnable(GL_LIGHT0); // Enable particular light source.
   glLightModelfv(GL_LIGHT_MODEL_AMBIENT, globAmb); // Global ambient light.
   glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE); // Enable two-sided lighting.
   glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE); // Enable local viewpoint.

   // Enable two vertex arrays: position and normal.
   glEnableClientState(GL_VERTEX_ARRAY);
   glEnableClientState(GL_NORMAL_ARRAY);

   // Specify locations for the position and normal arrays.
   glVertexPointer(3, GL_FLOAT, 0, vertices);
   glNormalPointer(GL_FLOAT, 0, normals);

   glColor3f(0.0, 0.0, 0.0);
}

// Drawing routine.
void drawScene()
{
   // Material property vectors.
   float matAmbAndDif1[] = {0.9, 0.0, 0.0, 1.0};
   float matAmbAndDif2[] = {0.0, 0.9, 0.0, 1.0};
   float matSpec[] = { 1.0, 1.0, 1.0, 1.0 };
   float matShine[] = { 50.0 };

   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

   glLoadIdentity();

   // Write message.
   glDisable(GL_LIGHTING); 
   glRasterPos3f(-1.0, 1.0, -2.0);
   if (averagedNormals) writeBitmapString((void*)font, "Averaged normals!");
   else writeBitmapString((void*)font, "Unaveraged normals!");
   glEnable(GL_LIGHTING); 

   // Position the box for viewing.
   gluLookAt(0.0, 3.0, 3.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

   // Material properties of the box.
   glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, matAmbAndDif1);
   glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, matSpec);
   glMaterialfv(GL_FRONT_AND_BACK, GL_SHININESS, matShine);

   if (averagedNormals) 
   // Averaged normals.
   {
      // Five sides of the box, excluding the top. The normal at each 
      // vertex is along the line from the origin to that vertex.
      glDrawElements(GL_QUADS, 20, GL_UNSIGNED_BYTE, quadIndices);

	  // The rotated lid (top side) of the box. 
      glPushMatrix();
      glTranslatef(0.0, 1.0, -1.0);
      glRotatef((float)step, -1.0, 0.0, 0.0);
      glTranslatef(0.0, -1.0, 1.0);
      glDrawElements(GL_QUADS, 4, GL_UNSIGNED_BYTE, &quadIndices[20]);
      glPopMatrix(); 
   }
   else
   // Unveraged normals.
   {
      // Six sides of the box, including the top, drawn with calls to the display list.
      glCallList(aSide); // Side 1.
   
      glPushMatrix();
      glRotatef(90.0, 1.0, 0.0, 0.0);
      glCallList(aSide); // Side 2.
      glPopMatrix();

      glPushMatrix();
      glRotatef(270.0, 1.0, 0.0, 0.0);
      glCallList(aSide); // Side 3.
      glPopMatrix();

      glPushMatrix();
      glRotatef(90.0, 0.0, 0.0, 1.0);
      glCallList(aSide); // Side 4.
      glPopMatrix();

      glPushMatrix();
      glRotatef(270.0, 0.0, 0.0, 1.0);
      glCallList(aSide); // Side 5.
      glPopMatrix();

      glPushMatrix();
      glTranslatef(0.0, 1.0, -1.0);
      glRotatef((float)step, -1.0, 0.0, 0.0);
      glTranslatef(0.0, -1.0, 1.0);
      glRotatef(180.0, 1.0, 0.0, 0.0);
      glCallList(aSide); // Top.
      glPopMatrix();
   }

   // Material properties of the sphere (only the front is ever seen).
   glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, matAmbAndDif2);

   // Cull the back faces of the sphere.
   glEnable(GL_CULL_FACE);
   glCullFace(GL_BACK);

   // Sphere.
   glutSolidSphere (1.0, 40, 40);
   
   glDisable(GL_CULL_FACE);

   glutSwapBuffers();
}

// OpenGL window reshape routine.
void resize (int w, int h)
{
   glViewport (0, 0, (GLsizei)w, (GLsizei)h);
   glMatrixMode (GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(60.0, (float)w/(float)h, 1.0, 20.0);
   glMatrixMode(GL_MODELVIEW);
}

// Keyboard input processing routine.
void keyInput(unsigned char key, int x, int y)
{
   switch (key) 
   {
      case 27:
         exit(0);
         break;
	  case ' ':
		 if (averagedNormals) averagedNormals = 0; else averagedNormals = 1;
		 glutPostRedisplay();
		 break;
      default:
         break;
   }
}

// Callback routine for non-ASCII key entry.
void specialKeyInput(int key, int x, int y)
{
   if(key == GLUT_KEY_UP) if (step < 180) step++;;
   if(key == GLUT_KEY_DOWN) if (step > 0) step--;;
   glutPostRedisplay();
}

// Routine to output interaction instructions to the C++ window.
void printInteraction(void)
{
   cout << "Interaction:" << endl;
   cout << "Press up/down arrow keys to open/close the box." << endl
	    << "Press space to toggle between averaged and unaveraged normals." << endl;
}

// Main routine.
int main(int argc, char **argv) 
{
   printInteraction();
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); 
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow ("sphereInBox2.cpp");
   setup();
   glutDisplayFunc(drawScene);
   glutReshapeFunc(resize);
   glutKeyboardFunc(keyInput);
   glutSpecialFunc(specialKeyInput);
   glutMainLoop();
   
   return 0;
}