/*******************************************************
Skeleton for a simple OpenGL program
Clicking the mouse starts and stops an object rotating
by R.S. Dannelly
*******************************************************/
#include <GL/glut.h>
#include <stdlib.h>

/***** Global Variables *****/
static GLfloat spin = 0.0;        // cumulative rotation 


/********************************************************
THIS IS THE PRIMARY DRAWING FUNCTION
********************************************************/
void display(void)
{
   glClearColor (0.0,0.0,0.0,0.0);  // clear to black
   glClear(GL_COLOR_BUFFER_BIT);
   glPushMatrix();                  // save transformation matrix
   glRotatef(spin, 1.0, 1.0, 0.0);

   /* place code for your lines here */

   glPopMatrix();                  // restore transformation matrix
   glFlush();
}

/********************************************************
The Reshape function is called when the window changes 
size or is initially created.
********************************************************/
void reshape(int w, int h)
{
   /* 1 : use the entire window */
   glViewport (0, 0, (GLsizei) w, (GLsizei) h);
   
   /* 2 : clear the Projection Matrix */
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();

   /* 3 : define the size of the universe */
   glOrtho(-50.0, 50.0, -50.0, 50.0, -50.0, 50.0);

   /* 4 : clear the Transformation Matrix */
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

/***********************************************************
Code for rotating
called when the CPU is idle and the mouse has been pressed
***********************************************************/
void spinDisplay (void)
{
  spin += 2.0;          // add to the spin global variable
  if (spin > 360.0)
     spin -= 360.0;
  glutPostRedisplay();  // update the display
}

/**************************************************
Mouse event handling routine
**************************************************/
void mouse(int button, int state, int x, int y)
{
   static int spinning = 0;

   // only process mouse clicks, not releases
   if (state == GLUT_DOWN) 
      if (!spinning)
        {
         spinning = 1;
         glutIdleFunc(spinDisplay);  // use available CPU time to spin
        }
      else
        {
         spinning = 0;
         glutIdleFunc(NULL);     // do nothing while idle
        } 
}

/********************************************************/
/*****   M A I N   **************************************/
/********************************************************/
 
int main(int argc, char** argv)
{
   /*** connect this client to the hardware ***/
   glutInit(&argc, argv);
   
   /*** create a window to draw into ***/
   glutInitDisplayMode (GLUT_RGB);
   glutInitWindowSize (500, 500); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);

   /*** do some work ***/
   glutDisplayFunc(display);  // how to draw 
   glutReshapeFunc(reshape);  // configure the world
   glutMouseFunc(mouse);      // mouse handler
   glutMainLoop();            // infinite loop
   return 0;  
}