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Chapter 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 load_module function.

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 the ionws and floatws workspace modules are provided. The formed provides the tiled workspaces familiar from older versions of Ion, while the latter provides the PWM flavour of conventional workspaces with freely ”floating” windows.

Workspace modules alone don't yet make the WM very usable. Better input capabilities are achieved through the query and menu modules. So-called drawing engines are also implemented as a modules, but they are not discussed here; see chapter 4.

The stock configuration for the 'ion' executable loads all the modules mentioned above. The stock configuration for the 'pwm' executable (which differs from the 'ion' executable in a few configuration details, such as Xinerama usage) does not load the ionws module.

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.

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.


    WObj
     |
     |-->WRegion
     |    |
     |    |-->WClientWin
     |    |
     |    |-->WWindow
     |    |    |
     |    |    |-->WRootWin
     |    |    |
     |    |    |-->WMPlex
     |    |    |    |
     |    |    |    |-->WScreen
     |    |    |    |
     |    |    |    |-->WGenFrame
     |    |    |         |
     |    |    |         |-->WIonFrame (ionws module)
     |    |    |         |
     |    |    |         |-->WFloatFrame (floatws module)
     |    |    |
     |    |    |-->WInput (query module)
     |    |         |
     |    |         |-->WEdln (query module)
     |    |         |
     |    |         |-->WMessage (query module)
     |    |
     |    |-->WGenWS
     |         |
     |         |-->WIonWS (ionws module)
     |         |
     |         |-->WFloatWS (floatws module)
     |
     |-->WWsSplit (ionws)
Figure 2.1: Ion class hierarchy. The string in parenthesis indicates the module in which this class is implemented if not in Ioncore.

The core classes:

WObj
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 great 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 again a virtual 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. WMPlexes include screens and the different types of 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.
WGenFrame
is another virtual class implementing what is common to the concrete frame classes but not all WMPlexes. While most Ion's objects have no graphical presentation, frames are basically the decorations around client windows (borders, tabs).
WGenWS
is a light virtual base class for different types of workspaces.

Classes implemented by the ionws module:

WIonWS
is the class for the usual tiled workspaces.
WIonFrame
implements the style of frames seen on WIonWSs.
WWsSplit
is an object internal to WIonWS implementation and stores the tree structure of the workspaces.

Classes implemented by the floatws module:

WFloatWS
is the class for the conventional workspaces where frames and other objects are allowed to ”float” around.
WFloatFrame
implements the frames seen on WFloatWSs decorated in the PWM style.

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. Quiries 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

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
          |
          |-->WIonWS:s and WFloatWS:s
          |
          |-->WClientWins in full screen mode
          |
          |-->WIonFrames and WFloatFrames
               |
               |-->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.


    WRootWins
     |
     |-->WScreens
          |
          |-->full screen WClientWins
          |    |
          |    |-->transient WClientWins (dialogs)
          |
          |-->WIonWSs
          |    |
          |    |-->WIonFrames
          |         |
          |         |-->WClientWins
          |         |    |
          |         |    |-->transient WClientWins (dialogs)
          |         |
          |         |-->a possible WEdln or WMessage
          |
          |-->WFloatWSs
               |
               |-->WFloatFrames
                    |
                    |-->WClientWins
                    |
                    |-->a possible WEdln or WMessage
Figure 2.3: Most common manager–managed relations

Note how the WClientWins managed by WFloatFrames don't have transients managed by them. This is because WFloatWSs choose to handle transients differently (transients are put in separate frames like normal windows; in the future they should be stacked above the frame containing the transient_for window).

2.2.3  Summary

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


1
the author doesn't like such artificial designs

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