Bachelor Thesis - Computer Graphics Group

are used. In any case, when no corresponding action can be found, an empty
Action object is returned.
Unlike the currently used PatternList, the active ActionMapping can be
modified safely. The next time a gesture is performed, the corresponding action
is determined according to the current state. This is beneficial as the user is
able to see the changes done in the user interface immediately. To achieve good
performance, the internal implementation uses QMap classes, which can be
indexed directly by an Application and a Gesture.
5.6 Commands
Action commands have been designed to be modular and easily extensible.
The interface is based on the command and prototype design patterns [1].
There are two classes of commands:
• ICommand is a basic command, which does not support configuration.
It must implement the execute method. A finalize method, which can
be overridden optionally, is also provided. This method is called when
wheel gestures are performed. The purpose is to finalize the sequence
of multiple command executions, each for one wheel-scrolling event. It
gives the command an opportunity to restore any state it might have
altered, such as releasing emulated key presses, etc.
• ICommandConfigurable is an extended variant of ICommand, which
is user configurable. It must implement methods, which store and restore
the actual command configuration in XML. To present the configuration
options in the user interface, the command implementation is supposed
to fill a provided container with any widgets it may need. It must be
also able to fill the widgets with the current configuration and to retrieve
the configuration from the widgets. This is done by implementing a few
virtual methods, prescribed by the interface
Instances of the actual command implementations are managed by the CommandFactory.
The factory is a globally accessible singleton, initialized by the
Engine at start-up. The factory owns prototypes of all available commands.
Other objects can browse the list of commands or directly request a certain
command by its name. If it has been found, the prototype of the command is
returned to the caller. Prototypes cannot be executed; they must be cloned to
create a separate instance.
A list of all commands with their descriptions can be found in the user’s
manual. Some of the commands have been proposed in the goals, others have
been designed while implementing the application.
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