/********************************/
/* Smooth walkthrought		    */
/* (C) Bedrich Benes 2004       */
/* this is NOT freeware         */
/* bbenes ~ at ~ purdue.edu     */
/********************************/
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>


//the main window size
//could be changed inside the resize callback
GLint wWindow=400;
GLint hWindow=200;


//position of the camera is cam, its angle is alpha
GLfloat cam[3],alpha;

//increments of position and angle
GLfloat deltaStep=0.f;
GLfloat deltaAlpha=0.f;

//possible objects in the scene
#define SPHERE 1
#define CUBE   2
#define TEAPOT 3


//radius of collision detection
#define RAD    0.4


//object positions and types
typedef struct ObjH
{
  GLfloat pos[3];
  GLubyte color[3];
  int type;
} ObjT;


int maxObj=6;
ObjT objs[] = {
				{{4,0,0},  {128,128,128},SPHERE},
				{{0,0,-4}, {255,255,0},  CUBE}, 
				{{10,0,-4},{0,0,255},    TEAPOT}, 
				{{10,0,4}, {255,0,255},  TEAPOT}, 
				{{6,0,3},  {255,255,0},  CUBE}, 
				{{5,0,-4}, {0,0,255},    CUBE} 
};


void Reshape(int w, int h)
{
  glViewport(0,0,w, h);       
  glEnable(GL_DEPTH_TEST);
//remember the settings for the camera
  wWindow=w;
  hWindow=h;
  //no transformations are needed here, the camera is set elsewhere
}



void RenderObjects()
{
  static GLint i; 

//draw the ground
  glBegin(GL_QUADS);
   glColor3ub(0,128,0);
   glVertex3f(-100,-0.6,-100);
   glVertex3f(100,-0.6,-100);
   glVertex3f(100,-0.6,100);
   glVertex3f(-100,-0.6,100);
  glEnd();

//draw the objects
  for (i=0;i<maxObj;i++)
  {
	glPushMatrix();
	glColor3ubv(objs[i].color);
	glTranslatef(objs[i].pos[0],objs[i].pos[1],objs[i].pos[2]);
	switch (objs[i].type)
	{
		case CUBE : {
						glutWireCube(0.5);
						break;
					}
		case TEAPOT : {
						glutWireTeapot(0.5);
						break;
					  }
		case SPHERE: {
						glutWireSphere(0.5,10,10);
						break;
					}
	}//of switch
    glPopMatrix();
  }//of for
}


//camera is at cam[]
//object is at obj[i].pos[]
void CheckCollisions()
{
  register i;
  for (i=0;i<maxObj;i++)
  {
    if ((cam[0]-objs[i].pos[0])*(cam[0]-objs[i].pos[0])+
		(cam[2]-objs[i].pos[2])*(cam[2]-objs[i].pos[2])<RAD) 
	{
		printf("Collision with object: %i\n",i);
		objs[i].color[0]=0;
		objs[i].color[1]=0;
		objs[i].color[2]=0;
	}
  }
}
	

void Display(void)
{
  static char needRedisplay;

  needRedisplay=0; //the scene does not move, last frame is actual
  glClearColor(1,1,1,1);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

  if (deltaAlpha || deltaStep)
  {
    alpha+=deltaAlpha;
	cam[0] -= (GLfloat)sin(alpha*3.14/180)*deltaStep;
    cam[2] -= (GLfloat)cos(alpha*3.14/180)*deltaStep;
	CheckCollisions();
	needRedisplay=1;
  }

//set the camera first
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(40,(GLfloat)wWindow/(GLfloat)hWindow,0.01,100);

//The coordinates of the transformations must be inverted!!
   glRotatef(-alpha,0,1,0);
   CheckCollisions();
   glTranslatef(-cam[0],-cam[1],-cam[2]);

//then the scene itself
   glMatrixMode(GL_MODELVIEW);
   RenderObjects();
//swap buffers
  glutSwapBuffers();  
  if (needRedisplay) glutPostRedisplay();
}


//+ and 0 shifts the camera up and down
void Kbd(unsigned char a, int x, int y)
{

	switch(a)
	{
 	  case '+' : cam[1]+=0.1;break;
 	  case '-' : cam[1]-=0.1;break;
 	  case 27 : exit(0);break;
	}
	glutPostRedisplay();
}


//special keys are responsible for the camera manipulation
//to make the motion smooth, the PRESS sets the step and alpha
//Release sets it to zero
void SpecKbdPress(int a, int x, int y)
{
   	switch(a)
	{
 	  case GLUT_KEY_LEFT  : deltaAlpha= 1.f;;break;
	  case GLUT_KEY_RIGHT : deltaAlpha=-1.f;;break;
 	  case GLUT_KEY_DOWN    : 
		  {
	  		deltaStep=-0.1;
			break;
		  }
	  case GLUT_KEY_UP  :
		  {
			deltaStep=0.1;
			break;
		  }

	}
	glutPostRedisplay();
}

void SpecKbdRelease(int a, int x, int y)
{
	switch(a)
	{
 	  case GLUT_KEY_LEFT  : deltaAlpha=0;break;
	  case GLUT_KEY_RIGHT : deltaAlpha=0;break;
 	  case GLUT_KEY_DOWN    : 
		  {
            deltaStep=0;	       
			break;
		  }
	  case GLUT_KEY_UP  :
		  {
            deltaStep=0;	       
			break;
		  }

	}
//	printf("\n%f %f",cam[0],cam[2]);
	glutPostRedisplay();
}


int main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
  glutInitWindowSize(wWindow,hWindow);
  glutCreateWindow("Scene walkthrough");
  glutIgnoreKeyRepeat(GL_FALSE);                     
  glutDisplayFunc(Display);
  glutReshapeFunc(Reshape);
  glutIgnoreKeyRepeat(1);//YES, ignore key repeat please
  glutKeyboardFunc(Kbd); //+ and -
  glutSpecialUpFunc(SpecKbdRelease); //smooth motion
  glutSpecialFunc(SpecKbdPress);
  glutMainLoop();
  return 0;        
}