/* trackball.c    */
/* Rotating cube demo with trackball*/
/* E. Angel, Interactive Computer Graphics */

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

#define bool int /* remove for C++ */
#define false 0
#define true 1

#ifndef M_PI
#define M_PI 3.14159265
#endif

int  winWidth, winHeight;
float  angle = 0.0, axis[3], trans[3];
bool  trackingMouse = false;
bool  redrawContinue = false;
bool    trackballMove = false;

/* Draw the cube.*/
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, int face)
{
  /* 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(1,0,3,2,0);
  polygon(3,7,6,2,1);
  polygon(7,3,0,4,2);
  polygon(2,6,5,1,3);
  polygon(4,5,6,7,4);
  polygon(5,4,0,1,5);
}

/* These functions implement a simple trackball-like motion control. */
float lastPos[3] = {0.0F, 0.0F, 0.0F};
int curx, cury;
int startX, startY;

void trackball_ptov(int x, int y, int width, int height, float v[3])
{
  float d, a;

  /* project x,y onto a hemi-sphere centered within width, height */
  v[0] = (2.0F*x - width) / width;
  v[1] = (height - 2.0F*y) / height;
  d = (float) sqrt(v[0]*v[0] + v[1]*v[1]);
  v[2] = (float) cos((M_PI/2.0F) * ((d < 1.0F) ? d : 1.0F));
  a = 1.0F / (float) sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);
  v[0] *= a;
  v[1] *= a;
  v[2] *= a;
}

void mouseMotion(int x, int y)
{
  float curPos[3], dx, dy, dz;

  trackball_ptov(x, y, winWidth, winHeight, curPos);
  if(trackingMouse)
  {
    dx = curPos[0] - lastPos[0];
    dy = curPos[1] - lastPos[1];
    dz = curPos[2] - lastPos[2];
    if (dx || dy || dz)
    {
      angle = 90.0F * sqrt(dx*dx + dy*dy + dz*dz);
      axis[0] = lastPos[1]*curPos[2] - lastPos[2]*curPos[1];
      axis[1] = lastPos[2]*curPos[0] - lastPos[0]*curPos[2];
      axis[2] = lastPos[0]*curPos[1] - lastPos[1]*curPos[0];
      lastPos[0] = curPos[0];
      lastPos[1] = curPos[1];
      lastPos[2] = curPos[2];
    }
  } 
  glutPostRedisplay();
}

void startMotion(int x, int y)
{
  trackingMouse = true;
  redrawContinue = false;
  startX = x; startY = y;
  curx = x; cury = y;
  trackball_ptov(x, y, winWidth, winHeight, lastPos);
  trackballMove=true;
}

void stopMotion(int x, int y)
{
  trackingMouse = false;
  if (startX != x || startY != y)
  {
    redrawContinue = true;
  }
  else
  {
    angle = 0.0F;
    redrawContinue = false;
    trackballMove = false;
  }
}

void display(void)
{
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
  /* view transform */
  if (trackballMove)
  {
    glRotatef(angle, axis[0], axis[1], axis[2]);
  }
  colorcube();
  glutSwapBuffers();
}

void mouseButton(int button, int state, int x, int y)
{
  if(button==GLUT_RIGHT_BUTTON) exit(0);
  if(button==GLUT_LEFT_BUTTON)
  {
    switch(state) 
    {
      case GLUT_DOWN:
        y=winHeight-y;
        startMotion( x,y);
        break;
      case GLUT_UP:
        stopMotion( x,y);
        break;
    }
  }
}

void myReshape(int w, int h)
{
  glViewport(0, 0, w, h);
  winWidth = w;
  winHeight = h;
}

void spinCube(void)
{
  if(redrawContinue) glutPostRedisplay();
}

int main(int argc, char *argv[])
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
  glutInitWindowSize(500, 500);
  glutCreateWindow("trackball");
  glutReshapeFunc(myReshape);
  glutDisplayFunc(display);
  glutIdleFunc(spinCube);
  glutMouseFunc(mouseButton);
  glutMotionFunc(mouseMotion);
  glEnable(GL_DEPTH_TEST); 
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0);
  glMatrixMode(GL_MODELVIEW);
  glutMainLoop();
  return 0;
}