# 4.3. For programmers

KTuberling isn't really difficult to extend for programmers.

## 4.3.1. C++ classes

TopLevel

  Top-level window and basic program management

ToDraw

  Description of one of the graphical "objects" to be drawn

## 4.3.2. .tuberling files structure

A .tuberling file holds all the necessary data to redraw a tuberling. It can be edited with an ordinary text editor.

There is one graphical object per line, in the order that is used to draw them. Each line contains 5 numbers: the identifier of the object, and the rectangle where it should be drawn (left, top, right, bottom). The numbers are separated by whitespaces.