Programming and Graphics

260 Introduction to C++ Programming and Graphics

As an example, the following function draws the solid disk shown in
Figure 8.1.1(d):

void disk()

{

int N=64;

float Dthet =2.0*3.1415926/N;

float centerx=0.0, centery=0.0;

float radius=1.0;

glClear(GLCOLORBUFFERBIT);

glBegin(GLTRIANGLEFAN);

glColor3f(0.8,0.5,0.2);

glVertex2f(centerx,centery);

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

{

float angle = i*Dtheta;

glVertex2f(cos(angle)*radius,sin(angle)*radius);

}

glEnd();

glFlush();

}

The disk is defined by a group ofNtriangles with one common vertex at the
disk center.

Cube

Three-dimensional graphics can be drawn in similar ways. The following
function paints the cube shown in Figure 8.1.1(e):

void cube(void)

{

glClear(GLCOLORBUFFERBIT);

/* Introduce a transformation matrix.

All vertices will be multiplied by this matrix */

glLoadIdentity(); // introduce the identity matrix

glOrtho(-8.0, 8.0, -8.0, 8.0, -8.0, 8.0); // set the axes

glTranslatef(-0.5, 0.2, 0.1); // translate the identity matrix

glRotatef(-50, 1.0, 0.0, 0.0); // rotate by 50 deg about the x axis

glRotatef(50, 0.0, 1.0, 0.0); // rotate by 50 deg about the y axis