Programming and Graphics

276 Introduction to C++ Programming and Graphics

void disk()

{

glClear(GLCOLORBUFFERBIT|GLDEPTHBUFFERBIT);

glColor3f(0.8,0.5,0.2);

centerx = centerx+Dx;

centery = centery+Dy;

if(centerx+radius > 1.0) Dx=-Dx;

if(centerx-radius < -1.0) Dx=-Dx;

if(centery+radius > 1.0) Dy=-Dy;

if(centery-radius <-1.0) Dy=-Dy;

glBegin(GLTRIANGLEFAN);

glVertex2f(centerx, centery);

for (int i=0; i <= N; i++)

{

float angle = i*Dtheta;

glVertex2f(centerx+cos(angle)*radius,

centery+sin(angle)*radius);

}

glEnd();

}

//--------- quit

void quit(unsigned char key, int x, int y)

{

if(key == ’q’)

{

cout << "Closing window " << endl;

glutDestroyWindow(win);

exit(0);

}

}

A snapshot of the animation is shown in Figure 8.2.1(b).

Rescaling

If we resize the graphics window, the displayed image will be distorted:
a circle will become an ellipse and a person will instantaneously lose or gain
weight. To prevent this, we run theglutRshapeFunccallback in the double
buffer mode.

The following code contained in the filepacman.ccdraws the image of
a Pac-Man whose shape remains unaltered when the window is resized: