main.cpp

#include "ofMain.h"
#include "ofApp.h"

//========================================================================
int main( ){
	ofSetupOpenGL(1024,768,OF_WINDOW);			// <-------- setup the GL context

	// this kicks off the running of my app
	// can be OF_WINDOW or OF_FULLSCREEN
	// pass in width and height too:
	ofRunApp(new ofApp());

}

ofApp.cpp

#include "ofApp.h"
#include "Square.h"

//--------------------------------------------------------------
void ofApp::setup(){
	const int marginx=80;
	const int blocksw = ofGetWidth()-marginx*2;
	const int offsetx = ofGetWidth()-blocksw-marginx;
	const int size    = blocksw/W;
	const int blocksh = size*H;
	const int offsety = (ofGetHeight()-blocksh)/2;
	for(int i=0;i<H;++i) {
		for(int j=0;j<W;++j) {
			const int left   = j*size + offsetx;
			const int top    = i*size + offsety;
			const ofColor color(ofRandom(255),ofRandom(255),ofRandom(255));
			Square square;
			square.setup(left,top,size,size,color);
			squares.emplace_back(square);
		}
	}
}

//--------------------------------------------------------------
void ofApp::update(){

}

//--------------------------------------------------------------
void ofApp::draw(){
	ofBackground(ofColor(10,10,10));
	for(auto& square: squares) {
		square.draw();
	}
}

//--------------------------------------------------------------
void ofApp::keyPressed(int key){

}

//--------------------------------------------------------------
void ofApp::keyReleased(int key){

}

//--------------------------------------------------------------
void ofApp::mouseMoved(int x, int y ){

}

//--------------------------------------------------------------
void ofApp::mouseDragged(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mousePressed(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mouseReleased(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mouseEntered(int x, int y){

}

//--------------------------------------------------------------
void ofApp::mouseExited(int x, int y){

}

//--------------------------------------------------------------
void ofApp::windowResized(int w, int h){

}

//--------------------------------------------------------------
void ofApp::gotMessage(ofMessage msg){

}

//--------------------------------------------------------------
void ofApp::dragEvent(ofDragInfo dragInfo){ 

}

ofApp.h

l#pragma once

#include "ofMain.h"
#include "Square.h"
#include <vector>

class ofApp : public ofBaseApp{
		static const int W = 10;
		static const int H = 6;
		std::vector<Square> squares;

	public:
		void setup();
		void update();
		void draw();

		void keyPressed(int key);
		void keyReleased(int key);
		void mouseMoved(int x, int y );
		void mouseDragged(int x, int y, int button);
		void mousePressed(int x, int y, int button);
		void mouseReleased(int x, int y, int button);
		void mouseEntered(int x, int y);
		void mouseExited(int x, int y);
		void windowResized(int w, int h);
		void dragEvent(ofDragInfo dragInfo);
		void gotMessage(ofMessage msg);
		
};

Square.cpp

#include "Square.h"

void Square::setup(int left,int top,int width,int height,ofColor color)
{
	this->left   = left;
	this->top    = top;
	this->width  = width;
	this->height = height;
	this->color  = color;
}

void Square::draw() {
	const int lw = 2; // linewidth
	ofPushStyle();
	ofSetColor(ofColor(50,50,50));
	ofDrawRectangle(left,top,width,height);
	ofSetColor(color);
	ofDrawRectangle(left+lw,top+lw,width-lw*2,height-lw*2);
	ofPopStyle();
}

void Square::clear() {
}

Square.h

#pragma once
#include "ofMain.h"

class Square {
	
public:
	void setup(int left,int top,int width,int height,ofColor color);
	void draw();
	void clear();

private:
	int left,top,width,height;
	ofColor color;
};