// OpenGL  program
// Illustrates interaction


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

//global variables
GLsizei wh = 500, ww = 500; /* initial window size */
GLfloat size = 3.0;         /* half side length of square */

//prototypes
void myinit();                      // OpenGL init
void display();                     // display callback
void myReshape(GLsizei, GLsizei);   // reshape callback 
void mouse(int btn, int state, int x, int y);   // callback
void keyboard(unsigned char key, int x, int y); //callback
void drawSquare(int x, int y);      // motion call back 
void demo_menu(int id);             //menu callback
 
/****************/
/***** MAIN *****/
/****************/
void main(int argc, char** argv)
{
   	glutInit(&argc,argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
	glutCreateWindow("square");
   	myinit();
   	glutReshapeFunc(myReshape);
   	glutKeyboardFunc(keyboard);
   	glutMotionFunc(drawSquare);

	glutCreateMenu(demo_menu);
    glutAddMenuEntry("quit", 1);
    glutAddMenuEntry("increase square size", 2);
    glutAddMenuEntry("decrease square size", 3);
    glutAttachMenu(GLUT_RIGHT_BUTTON);

	glutDisplayFunc(display);

   	glutMainLoop();
}

/********************************/
/***** FUNCTION DEFINITIONS *****/
/********************************/

/*****************************************************************/
// init steps
/*****************************************************************/
void myinit()
{
	/* set viewing conditions */
	glViewport(0,0,ww,wh);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0.0, (GLdouble) ww, 0.0, (GLdouble) wh, -1, 1);
	glMatrixMode(GL_MODELVIEW);

	/* clear color buffer stuff */
	glClearColor(0.0, 0.0, 0.0, 1.0); //black
	glClear(GL_COLOR_BUFFER_BIT);
	glFlush();
}



/*****************************************************************/
// Keyboard callback, keyboard events:
// Quit the program on press of letter q or Q
/*****************************************************************/

void keyboard(unsigned char key, int x, int y)
{ 
    if (key=='q' || key=='Q') exit(0);
}

/*****************************************************************/
// Reshape callback, window events:
// Ajust projection according to new winow parameters
/*****************************************************************/
void myReshape(GLsizei w, GLsizei h)
{
    /* adjust clipping box */
   	glMatrixMode(GL_PROJECTION);
   	glLoadIdentity(); 
   	glOrtho(0.0, (GLdouble)w, 0.0, (GLdouble)h, -1.0, 1.0);
   	glMatrixMode(GL_MODELVIEW);
   	glLoadIdentity(); 
    /* adjust viewport and clear */
	glViewport(0,0,w,h);
    glClearColor (0.0, 0.0, 0.0, 1.0);
   	glClear(GL_COLOR_BUFFER_BIT);
	
   	glFlush();
    /* set global size for use by drawing routine */
	ww = w;
   	wh = h; 
}

/*****************************************************************/
// Motion callback:
// Draws a square of random color at x,y screen position
/*****************************************************************/
void drawSquare(int x, int y)
{
	  y=wh-y;
	  glColor3ub( (char) rand()%256, (char) rand()%256, 
		(char) rand()%256);
	  glBegin(GL_POLYGON);
	 	glVertex2f(x+size, y+size);
		glVertex2f(x-size, y+size);
	 	glVertex2f(x-size, y-size);
	   	glVertex2f(x+size, y-size);
	  glEnd();
	  glFlush();
}


/*****************************************************************/    
// display callback
/*****************************************************************/

void display()
{
    
}

/*****************************************************************/    
// menu callback
/*****************************************************************/

void demo_menu(int id)
{
    if (id==1) exit (0);
    else if (id==2) size = 2* size;
    else if (size > 1) size = size/2;
	glClearColor (0.0, 0.0, 0.0, 1.0);
   	glClear(GL_COLOR_BUFFER_BIT);
   	glFlush();
    glutPostRedisplay( );
}