/*
 *  This program demonstrates double buffering for flicker-free animation.
 *  Originally written by Edward Angel, and only slightly adapted by Scott
 *  D. Anderson.
 */

#include <stdlib.h>
// This program doesn't actually use TW, but <tw.h> includes glut.h and
// other header files.
#include <tw.h>

const int WinSize = 400;
static GLfloat spinAngle = 0.0;
int SingleBufferWindow;
int DoubleBufferWindow;

void displayDoubleBuffering(void)
{
    glClear (GL_COLOR_BUFFER_BIT);

    glRectf (-25.0, -25.0, 25.0, 25.0);

    glFlush();
    glutSwapBuffers ();
}

void displaySingleBuffering(void) {
    glClear(GL_COLOR_BUFFER_BIT);

    glRectf(-25.0, -25.0, 25.0, 25.0);

    glFlush();
}

void spinDisplay (void) {
    spinAngle = spinAngle + 1.0;
    if (spinAngle > 360.0)
	spinAngle = spinAngle - 360.0;
    glutSetWindow(SingleBufferWindow);
    glLoadIdentity();
    glRotatef (spinAngle, 0, 0, 1);
    glutPostRedisplay(); 
    glutSetWindow(DoubleBufferWindow);
    glLoadIdentity();
    glRotatef (spinAngle, 0, 0, 1);
    glutPostRedisplay();
}

void myinit (void) {
    glClearColor(0, 0, 0, 1);
    glColor3f(1, 1, 1);
    glShadeModel(GL_FLAT);
}

bool Animate = false;

void keys(unsigned char key, int x, int y) {
    switch(key) {
    case ' ':
	Animate = !Animate;
	if(Animate)
	    glutIdleFunc(spinDisplay);
	else
	    glutIdleFunc(NULL);
	break;
    default:
	exit(0);
    }
}

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 ();
}

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

    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(WinSize,WinSize);
    glutInitWindowPosition(0,0);
    SingleBufferWindow=glutCreateWindow("single buffered");
    myinit ();
    glutDisplayFunc(displaySingleBuffering); 
    glutReshapeFunc (myReshape);
    glutIdleFunc (NULL);
    glutKeyboardFunc(keys);

    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(WinSize,WinSize);
    glutInitWindowPosition(WinSize+50,0);
    DoubleBufferWindow=glutCreateWindow("double buffered");
    myinit ();
    glutDisplayFunc(displayDoubleBuffering);
    glutReshapeFunc (myReshape);
    glutIdleFunc (NULL);
    glutKeyboardFunc(keys);

    glutMainLoop();

}