/*
 *  double.c
 *  This program demonstrates double buffering for
 *  flicker-free animation.  The left and middle mouse
 *  buttons start and stop the spinning motion of the square.
 */
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>

#define DEGREES_TO_RADIANS 3.14159/180.0

static GLfloat spin = 0.0;
GLfloat x, y;
int singleb, doubleb;

void square()
{
    glBegin(GL_QUADS);
       glVertex2f(x,y);
       glVertex2f(-y,x);
       glVertex2f(-x,-y);
       glVertex2f(y,-x);
    glEnd();
}


void displayd()
{
    glClear (GL_COLOR_BUFFER_BIT);
    square();
    glutSwapBuffers ();
}

void displays()
{
    glClear (GL_COLOR_BUFFER_BIT);
    square();
    glFlush();
}

void spinDisplay ()
{
    spin = spin + 2.0;
    if (spin > 360.0) spin = spin - 360.0;
    x= 25.0*cos(DEGREES_TO_RADIANS * spin);
    y= 25.0*sin(DEGREES_TO_RADIANS * spin);
    glutSetWindow(singleb);
    glutPostRedisplay();
    glutSetWindow(doubleb);
    glutPostRedisplay();
}

void myinit ()
{
    glClearColor (0.0, 0.0, 0.0, 1.0);
    glColor3f (1.0, 1.0, 1.0);
    glShadeModel (GL_FLAT);
}

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

void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
    glOrtho (-50.0, 50.0, -50.0*(GLfloat)h/(GLfloat)w,
        50.0*(GLfloat)h/(GLfloat)w, -1.0, 1.0);
    else
    glOrtho (-50.0*(GLfloat)w/(GLfloat)h,
        50.0*(GLfloat)w/(GLfloat)h, -50.0, 50.0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
}

/*  main loop
 *  open window with initial window size, title bar,
 *  RGBA display mode, and handle input events
 */
int main(int argc, char** argv)
{

    glutInit(&argc,argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    singleb=glutCreateWindow("single buffered");
    myinit ();
    glutDisplayFunc(displays);
    glutReshapeFunc (myReshape);
    glutIdleFunc (spinDisplay);
    glutMouseFunc (mouse);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    doubleb=glutCreateWindow("double buffered");
    myinit ();
    glutDisplayFunc(displayd);
    glutReshapeFunc (myReshape);
    glutIdleFunc (spinDisplay);
    glutMouseFunc (mouse);

    glutMainLoop();

}
