/* turtle.c   31 January 2000 */

/* 
  John Burkardt

  This program illustrates a simple use of the mouse buttons to control
  an OpenGL graphics program.

  A line of a certain color is always being drawn on the screen.

  Each time the LEFT button is clicked, the line turns left 95 degrees
  and the line color is modified. 

  A RIGHT button makes a right turn of 95 degrees and a color change. 

  The MIDDLE button stops the program.

*/
#include "stdio.h"
#include <stdlib.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glx.h>
#include <GL/glut.h>

/* 
  Define a 2D point data type.
*/

typedef struct { float x, y;} point_2d;

/*
  Cosine and sine of 95 degrees.
*/
float c = -0.087155;
float s =  0.996195;

float r = 0.0;
float g = 0.2;
float b = 0.0;

float window_xmin = 0.0;
float window_xmax = 600.0;

float window_ymin = 0.0;
float window_ymax = 400.0;

point_2d mid = { 250.0, 250.0 };
point_2d new = { 250.0, 250.0 };
point_2d old = { 250.0, 250.0 };

point_2d direction = { 1.0, 0.0 };

void clear ( void ) {
  glClear ( GL_COLOR_BUFFER_BIT );
}

void display ( void )

/* 
  DISPLAY draws little line segments in the current direction.
*/

{
  float delta = 0.01;
/*
  If the point goes out of the region, make it come in the other side.
*/
  new.x = old.x + delta * direction.x; 
  new.y = old.y + delta * direction.y;
/*
  Take care of simple wraparound cases.
*/
  if ( new.x < window_xmin ) {

    mid.x = window_xmin;
    mid.y = old.y + ( ( mid.x - old.x ) / direction.x ) * direction.y;
    glBegin ( GL_LINES );
      glVertex2f ( old.x, old.y );
      glVertex2f ( mid.x, mid.y );
    glEnd ( );

    mid.x = window_xmax;
    new.x = new.x + window_xmax;
    glBegin ( GL_LINES );
      glVertex2f ( mid.x, mid.y );
      glVertex2f ( new.x, new.y );
    glEnd ( );

  }
  else if ( new.x > window_xmax ) {

    mid.x = window_xmax;
    mid.y = old.y + ( ( mid.x - old.x ) / direction.x ) * direction.y;
    glBegin ( GL_LINES );
      glVertex2f ( old.x, old.y );
      glVertex2f ( mid.x, mid.y );
    glEnd ( );

    mid.x = window_xmin;
    new.x = new.x - window_xmax;
    glBegin ( GL_LINES );
      glVertex2f ( mid.x, mid.y );
      glVertex2f ( new.x, new.y );
    glEnd ( );
  }
  else if ( new.y < window_ymin ) {

    mid.y = window_ymin;
    mid.x = old.x + ( ( mid.y - old.y ) / direction.y ) * direction.x;
    glBegin ( GL_LINES );
      glVertex2f ( old.x, old.y );
      glVertex2f ( mid.x, mid.y );
    glEnd ( );

    mid.y = window_ymax;
    new.y = new.y + window_ymax;
    glBegin ( GL_LINES );
      glVertex2f ( mid.x, mid.y );
      glVertex2f ( new.x, new.y );
    glEnd ( );

  }
  else if ( new.y > window_ymax ) {

    mid.y = window_ymax;
    mid.x = old.x + ( ( mid.y - old.y ) / direction.y ) * direction.x;
    glBegin ( GL_LINES );
      glVertex2f ( old.x, old.y );
      glVertex2f ( mid.x, mid.y );
    glEnd ( );

    mid.y = window_ymin;
    new.y = new.y - window_ymax;
    glBegin ( GL_LINES );
      glVertex2f ( mid.x, mid.y );
      glVertex2f ( new.x, new.y );
    glEnd ( );
  }
  else {
  
    glBegin ( GL_LINES );
      glVertex2f ( old.x, old.y );
      glVertex2f ( new.x, new.y );
    glEnd ( );

  }

  old.x = new.x;
  old.y = new.y;

  glFlush();
}

void mouse ( int btn, int state, int x, int y ) {

/*
  Respond to user mouse button input.
*/
  float temp;

  if ( state == GLUT_DOWN ) {

    if ( btn == GLUT_LEFT_BUTTON ) {

      r = r / 2.0;
      b = ( 1.0 + b ) / 2.0;
      glColor3f ( r, g, b );

      temp =          c * direction.x - s * direction.y;
      direction.y = + s * direction.x + c * direction.y;
      direction.x = temp;

      glutIdleFunc ( display );
    }
    else if ( btn == GLUT_RIGHT_BUTTON ) {

      r = ( 1.0 + r ) / 2.0;
      b = 2.0 * b;
      glColor3f ( r, g, b );

      temp =          c * direction.x + s * direction.y;
      direction.y = - s * direction.x + c * direction.y;
      direction.x = temp;

      glutIdleFunc ( display );
    }
    else if ( btn == GLUT_MIDDLE_BUTTON ) {
      printf ( "Bye bye!\n" );
      exit ( 0 );
    }
  }
}

int main ( int argc, char** argv ) {

  glutInit ( &argc, argv );
  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize ( window_xmax - window_xmin, window_ymax - window_ymin );
  glutInitWindowPosition ( 0, 0 );
  glutCreateWindow ( "Mouse Patrol" );

  glutIdleFunc (display);
  glutMouseFunc ( mouse );  
  glClearColor ( 0.9, 0.9, 0.9, 0.0 );
  glColor3f ( r, g, b );

  glMatrixMode ( GL_PROJECTION );
  glLoadIdentity ( );
  gluOrtho2D ( window_xmin, window_xmax, window_ymin, window_ymax );
  glMatrixMode ( GL_MODELVIEW );

  glutDisplayFunc ( clear );

  glutMainLoop();

}