#include <GL/glut.h>
#include <cmath>
#include <cstdlib>

/*
In this lab, we will modify an OpenGL program to study Double-Buffering

  #1
  Note again that the 400 x 400 window is mapped to a frame where the origin, (0,0), 
  is in the middle.  Compile and run the code as-is.  What happens when you click on
  the left and right mouse buttons?

  #2
  Now try it with the screen maximized.  What changed?


  #3
  Turn on double buffering.  Look for the comments in the code below.

*/

#define WINDOW 400
#define LENGTH WINDOW/4.0
#define PI 4.0*atan(1.0)

GLfloat theta=45.0;

void myInit ()
{
	glClearColor( 1.0 , 1.0 , 1.0 , 0.0 );
	glColor3f( 0.0 , 0.0 , 0.0 );

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(-WINDOW/2.0 , WINDOW/2.0 , -WINDOW/2.0 , WINDOW/2.0);
	glMatrixMode(GL_MODELVIEW);
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT);

	GLfloat thetar;
	GLfloat a,b;

	thetar = 2.0*PI*theta/360.0;
	a = LENGTH*cos(thetar);
	b = LENGTH*sin(thetar);

	glBegin(GL_POLYGON);
		glColor3f(1.0,0.0,0.0);
		glVertex2f(a,b);
		glColor3f(0.0,1.0,0.0);
		glVertex2f(-b,a);
		glColor3f(0.0,0.0,1.0);
		glVertex2f(-a,-b);
		glColor3f(0.5,0.5,0.5);
		glVertex2f(b,-a);
	glEnd();

	// switch the following lines
	glFlush();
	//glutSwapBuffers();
}

void spinDisplay() {
	theta+=0.5;
	glutPostRedisplay();
}


void mouse (GLint btn, GLint state, GLint x, GLint y)
{
	if (btn==GLUT_LEFT_BUTTON && state==GLUT_DOWN) {
		glutIdleFunc(spinDisplay);
	}
	if (btn==GLUT_RIGHT_BUTTON && state==GLUT_DOWN) {
		glutIdleFunc(NULL);
	}

}


int main (int argc, char ** argv) {
	glutInit(&argc,argv);

	// switch the following lines
	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
	//glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB );

	glutInitWindowSize(WINDOW,WINDOW);
	glutInitWindowPosition(0,0);
	glutCreateWindow("rotatin");
	glutDisplayFunc(display);
	glutMouseFunc(mouse);
	myInit();
	glutMainLoop();

	return 0;
}