In C++ language specification each project must have a .cpp file with the defined main() function. This function is an entry point for an operating system to start the application. In openFrameworks, the main() function is contained in the main.cpp file. The most important line of the function is the following:

ofSetupOpenGL( &window, 1024, 768, OF_WINDOW );

This ofSetupOpenGL() function calling instructs openFrameworks that you need to create a window for visual output with the width 1024 and height 768 pixels. The last parameter OF_WINDOW means that you need to create a window, which the user can move and resize on the desktop screen. If you specify the last parameters as OF_FULLSCREEN, the project will run at full screen—such a mode is important for many projects.

For example, if you need to show your project on the full screen with dimensions 1920 x 1024 pixels, you can do it by replacing the ofSetupOpenGL() call with the following line:

ofSetupOpenGL( &window, 1920, 1024, OF_FULLSCREEN );

Normally you need not change the main.cpp file at all, because the settings of screen size can be done in the testApp.cpp text, which we consider now.

This file begins with #pragma once. This is a compiler directive, which should be present at the beginning of all the .h files. The next line is #include "ofMain.h". It includes openFrameworks' core classes and functions. After this, the code contains declaration of the testApp class, which is inherited from the openFrameworks' ofBaseApp class:

#pragma once

#include "ofMain.h"

class testApp : public ofBaseApp{
public:
  //openFrameworks' standard functions declarations
  void setup();
  void update();
  void draw();

  //...

  //Declarations of custom objects for the project
  ofEasyCam cam;      
  ofMesh mesh;
  ofImage img;
};

The testApp class contains a number of functions, setup(), update(), draw(), and some others. These are the functions required for your project to work. They are defined in the ofBaseApp class and called by openFrameworks. (The linking of the testApp class to the openFrameworks engine is done within the main() function. Its last line creates an object of this class and links it to the window, controlled by openFrameworks.) We will describe the meaning of the functions in the next section.

In the end of the class definition you will see declarations of the cam, mesh, and img objects. These are custom objects defined just in this example. In your own projects, you should add declarations of your objects here too.

Let's sum up: when creating your own project you should keep declarations of the setup(), update(), draw() functions, and others untouched, and also add your objects' and functions' declarations, which are needed for your project.

The testApp.cpp file contains definitions of all functions, declared in testApp.h. Let's explain the standard functions of the testApp class.

The most important functions are setup(), update(), and draw(). setup() is called first, and then update() and draw() are called in an infinite cycle, until the user presses the Esc key to close the project:

Let's consider these functions in detail.