2 Preliminaries: Key concepts and relations

The purpose of this chapter to explain some of key concepts and relations you need to understand before reading the following chapters. These include modules explained in section 2.1 and the Ion class and object hierarchies, section 2.2.

2.1 Modules

Ion has been designed so that the 'ion' executable only implements some basic services on top of which very different kinds of window managers could be build by loading the appropriate 'modules'. On modern system these modules are simply dynamically loaded .so libraries. On more primitive systems, or if you want to squeeze total size of the executable and libraries, the modules can optionally be statically linked to the main binary, but must nevertheless be loaded with the dopath function. Modules may also include Lua code.

If no modules are loaded, all client windows appear in full screen mode. To get better window management support, one or more workspace modules should be loaded. Currently Ion provides the following workspace modules

mod_ionws: Tiled workspaces of the original Ion kind.
mod_floatws: Conventional workspaces with freely floating frames of the PWM flavour.
mod_panews: Tiled workspaces with automatic tiling in a template layout based on silly heuristics or winprop (see section 3.5).

Workspace modules alone don't yet make the WM very usable. At the least the mod_query and mod_menu modules should be loaded for better input capabilities. The full list of additional modules is as follows

mod_query: Queries (for starting programs and so on) and message boxes.
mod_menu: Support for menus, both pull-down and keyboard-operated in-frame menus.
mod_statusbar: Module that implements a statusbar that can be adaptively embedded in each workspace's layout.
mod_dock: Module for docking Window Maker dockapps. The dock can both float and be embedded as the statusbar.
mod_sp: This module implements a scratchpad frame that can be toggled on/off everywhere. Think of the 'console' in some first-person shooters.
mod_mgmtmode: Support module for implementing ''management modes'' with a XOR-frame similar to move/resize mode around selected region.
mod_sm: Session management support module. Loaded automatically when needed!

So-called drawing engines are also implemented as a modules, but they are not discussed here; see chapter 4.

The stock configuration for the 'ion3' executable loads all of the modules mentioned above except mod_dock and filemod_mgmtmode. The stock configuration for the 'pwm3' executable (which differs from the 'ion3' executable in a few configuration details, such as Xinerama usage) only load mod_floatws, mod_menu and mod_query.

2.2 Class and object hierarchies

While Ion does not not have a truly object-oriented design ¹, things that appear on the computer screen are, however, quite naturally expressed as such ''objects''. Therefore Ion implements a rather primitive OO system for these screen objects and some other things.

It is essential for the module writer to learn this object system, but also people who write their own binding configuration files necessarily come into contact with the class and object hierarchies -- you need to know which binding setup routines apply where, and what functions can be used as handlers in which bindings. It is the purpose of this section to attempt to explain these hierarchies. If you do not wish the read the full section, at least read the summary at the end of it, so that you understand the very basic relations.

For simplicity we consider only the essential-for-basic-configuration Ioncore, mod_ionws and mod_query classes. See Appendix B for the full class hierachy visible to Lua side.

2.2.1 Class hierarchy

One of the most important principles of object-oriented design methodology is inheritance; roughly how classes (objects are instances of classes) extend on others' features. Inheritance gives rise to class hierarchy. In the case of single-inheritance this hierarchy can be expressed as a tree where the class at the root is inherited by all others below it and so on. Figure 2.1 lists out the Ion class hierarchy and below we explain what features of Ion the classes implement.

    Obj
     |-->WRegion
     |    |-->WClientWin
     |    |-->WWindow
     |    |    |-->WRootWin
     |    |    |-->WMPlex
     |    |    |    |-->WScreen
     |    |    |    |-->WFrame
     |    |    |-->WInput (mod_query)
     |    |         |-->WEdln (mod_query)
     |    |         |-->WMessage (mod_query)
     |    |-->WGenWS
     |         |-->WIonWS (mod_ionws)
     |-->WSplit (mod_ionws)

Figure 2.1: Ioncore, mod_ionws and mod_query class hierarchy.

The core classes:

Obj: Is the base of Ion's object system.
WRegion: is the base class for everything corresponding to something on the screen. Each object of type WRegion has a size and position relative to the parent WRegion. While a big part of Ion operates on these instead of more specialised classes, WRegion is a ''virtual'' base class in that there are no objects of ''pure'' type WRegion; all concrete regions are objects of some class that inherits WRegion.
WClientWin: is a class for client window objects, the objects that window managers are supposed to manage.
WWindow: is the base class for all internal objects having an X window associated to them (WClientWins also have X windows associated to them).
WRootWin: is the class for root windows of X screens. Note that an ''X screen'' or root window is not necessarily a single physical screen as a root window may be split over multiple screens when multi-head extensions such as Xinerama are used. (Actually there can be only one WRootWin when Xinerama is used.)
WMPlex: is a base class for all regions that''multiplex'' other regions. This means that of the regions managed by the multiplexer, only one can be displayed at a time. Classes that inhereit WMPlex include screens and frames.
WScreen: is the class for objects corresponding to physical screens. Screens may share a root window when Xinerama multihead extensions are used as explained above.
WFrame: is the class for frames. While most Ion's objects have no graphical presentation, frames basically add to WMPlexes the decorations around client windows (borders, tabs).
WGenWS: is a light base class for different types of workspaces.

Classes implemented by the ionws module:

WIonWS: is the class for the usual tiled workspaces.
WSplit: (or, more specifically, classes that inherit it) encode the WIonWS tree structure.

Classes implemented by the query module:

WInput: is a virtual base class for the two classes below.
WEdln: is the class for the ''queries'', the text inputs that usually appear at bottoms of frames and sometimes screens. Queries are the functional equivalent of ''mini buffers'' in many text editors.
WMessage: implements the boxes for warning and other messages that Ion may wish to display to the user. These also usually appear at bottoms of frames.

2.2.2 Object hierarchies: WRegion parents and managers

Parent--child relations

Each object of type WRegion has a parent and possibly a manager associated to it. The parent for an object is always a WWindow and for WRegion with an X window (WClientWin, WWindow) the parent WWindow is given by the same relation of the X windows. For other WRegions the relation is not as clear. There is generally very few restrictions other than the above on the parent---child relation but the most common is as described in Figure 2.2.

    WRootWins
     |-->WScreens
          |-->WIonWSs
          |-->WClientWins in full screen mode
          |-->WFrames
               |-->WClientWins, including transients
               |-->a possible WEdln or WMessage

Figure 2.2: Most common parent--child relations

WRegions have very little control over their children as a parent. The manager WRegion has much more control over its managed WRegions. Managers, for example, handle resize requests, focusing and displaying of the managed regions. Indeed the manager---managed relationship gives a better picture of the logical ordering of objects on the screen. Again, there are generally few limits, but the most common hierarchy is given in Figure 2.3. Note that sometimes the parent and manager are the same object and not all objects may have a manager (e.g. the dock in the dock module at the time of writing this) but all have a parent--a screen if not anything else.

Manager--managed relations

    WRootWins
     |-->WScreens
          |-->full screen WClientWins
          |    |-->transient WClientWins (dialogs)
          |-->WScratchpad
          |-->WIonWSs/WFloatWS/WPaneWS
               |-->WFrames
               |    |-->WClientWins
               |    |    |-->transient WClientWins (dialogs)
               |    |-->possibly a WEdln or WMessage
               |-->WIonWSs/WFloatWS/WPaneWS

Figure 2.3: Most common manager--managed relations

Note that a workspace can manage another workspace. This can be achieved with the attach_new function, and allows you to nest workspaces as deep as you want.

2.2.3 Summary

In the standard setup, keeping queries, messages and menus out of consideration:

The top-level objects that matter are screens and they correspond to physical screens. The class for screens is WScreen.
Screens contain (multiplex) workspaces and full screen client windows. Only one of them can be viewed at a time. Workspace classes are WIonWS and WFloatWS for the two different types of workspaces (and WGenWS).
Frames are managed by workspaces. Frames are the objects with decorations such as tabs and borders.
Frames contain (multiplex) client windows, to each of which corresponds a tab in the frame's decoration. Only one client window (or other object) can be shown at a time in each frame. The class for client windows is WClientWin.

1: the author doesn't like such artificial designs