| OpenTTD
    | 
|  Dirty | Handles the repaint of some part of the screen | 
|  Snowline functions and data structures | |
|  Rows and columns in the viewport | Columns are vertical sections of the viewport that are half a tile wide | 
|  Hierarchical widgets | Hierarchical widgets, also known as nested widgets, are widgets stored in a tree | 
|  Hierarchical widget parts | To make nested widgets easier to enter, nested widget parts have been created | 
 1.8.1.2
 1.8.1.2