Programming and Graphics

266 Introduction to C++ Programming and Graphics

int N=4;

float Dtheta = 2*3.1415926/N;

float centerx = 0.0, centery = 0.0;

float radius1 = 0.5;

float radius2 = 1.0;

glClear(GLCOLORBUFFERBIT);

glBegin(GLQUADS);

for (int i=1; i<= N; i++)

{

float angle1 = (i-1)*Dtheta;

float angle2 = i*Dtheta;

if(i==1)

{

centerx = 0.1;

centery = 0.1;

}

else if(i==2)

{

centerx = -0.1;

centery = 0.1;

}

else if(i==3)

{

centerx = -0.1;

centery = -0.1;

}

else

{

centerx = 0.1;

centery = -0.1;

}

glColor3f(0.2,0.5,0.2);

glVertex2f(centerx+cos(angle1)*radius1 ,centery+sin(angle1)*radius1);

glColor3f(0.8,0.5,0.2);

glVertex2f(centerx+cos(angle1)*radius2 ,centery+sin(angle1)*radius2);

glColor3f(0.8,0.5,0.2);

glVertex2f(centerx+cos(angle2)*radius2 ,centery+sin(angle2)*radius2);

glColor3f(0.2,0.5,0.2);

glVertex2f(centerx+cos(angle2)*radius1 ,centery+sin(angle2)*radius1);

}

glEnd();

glFlush();

}

Note that OpenGL allows us to set the vertex color, which is then automatically
interpolated over the surface of a quadrilateral.