generatePieMesh.h

#pragma once
#include "ofMain.h"

ofMesh generatePieMesh( float radius, float segments ) {
    
    // Create our mesh.
    ofMesh mesh;
    mesh.setMode( OF_PRIMITIVE_TRIANGLE_FAN );
    
    // Add the center point
    mesh.addVertex( ofVec3f::zero() );
    // Say it is the first point
    mesh.addIndex( 0 );
    
    // Add the outer points rc1 had i< segments and it missed the last segment
    for ( float i = 0; i <= segments; ++i ) {
        
        // Use our matrix to plot the points.
        // Because I can't be bothered doing the trig :)
        ofMatrix4x4 matrix;
        // This is done backwards
        // 1. Move to the outside
        matrix.translate( 0.0f, radius, 0.0f );
        // 2. Make a segment the size of one segment
        matrix.rotate( (360 / segments) * (i / segments), 0.0, 0.0, 1.0 );
        // 3. Invert the scale so it works clockwise
        matrix.scale( 1.0, -1.0, 1.0 );
        
        // Create a point at zero and multiply it by our matrix
        ofVec3f p = ofVec3f::zero() * matrix;
        // Add the point
        mesh.addVertex( p );
        // Set the point index
        mesh.addIndex( i + 1 );
    }
    
    return mesh;
}

ofApp.cpp

#include "ofApp.h"
#include "generatePieMesh.h"

//--------------------------------------------------------------
void ofApp::setup(){
    
    numClones = 72;
    
    // Pre-generate a pi
    pie = generatePieMesh( 650.0, numClones );
}

//--------------------------------------------------------------
void ofApp::draw(){
    
    // Example 2
    // =========
    
    ofPushMatrix(); // Background wheel matrix
    ofPushStyle();
        ofTranslate(ofGetWindowWidth()/2, ofGetWindowHeight()/2);
        ofSetColor(0); // Set back wheel to black
        
            // Draw the requisite no of clones, rotating and spacing them out
        for (int i=0; i<numClones/2; i++) {
            glRotatef(2 *(360 / numClones), 0, 0, 1);
            pie.draw();
        }
        
    ofPopStyle();
    ofPopMatrix();
    
    
}

ofApp.h

#pragma once

#include "ofMain.h"

class ofApp : public ofBaseApp{
  public:
    void setup();
    void draw();

    ofMesh pie;
    float numClones;
};