static frustumMode_t frustumMode = LETTERBOX;
static GLdouble aspectRatio;		// of the Frustum

static GLint windowWidth;
static GLint windowHeight;
// and saved values of the same
static GLint windowWidth_old;
static GLint windowHeight_old;

// Sets the three global variables for the windowWidth, windowHeight, and
// aspectRatio.
void setWindow(GLint ww, GLint wh) {
    windowWidth=ww;
    windowHeight=wh;
    aspectRatio=((GLdouble)ww)/((GLdouble) wh);
    twMessage(TW_WINDOW,"window = (%d,%d), aspect ratio = %f\n",
	      ww,wh,aspectRatio);
}

// Reshape Callback
void twReshapeFunction(int w,int h) {
    setWindow(w,h);
}

void twInitWindowSize(GLint xsize, GLint ysize) {
  glutInitWindowSize(xsize,ysize);
  windowWidth=xsize;
  windowHeight=ysize;
}

void twFullScreen() {
    twMessage(TW_WINDOW,"switch to full screen, saving %d x %d",
	      windowWidth,windowHeight);
    windowWidth_old = windowWidth;
    windowHeight_old = windowHeight;
    glutFullScreen();
}

void twWindow() {
    twMessage(TW_WINDOW,"back to %d x %d window\n",
	      windowWidth_old,windowHeight_old);
    glutReshapeWindow(windowWidth_old,windowHeight_old);
    glutPositionWindow(0,0);
}