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<H2> 6.2 System Library (<CODE>csSys</CODE>) </H2>
<!--docid::SEC292::-->
<P>
The system library is the basic module in every Crystal Space application. It
contains one main class, the <EM>system driver</EM>. This driver helps in
several ways:
</P><P>
WARNING! The system library is currently being eliminated. Soon the
information here will be outdated (and then rewritten).
</P><P>
<UL>
<LI>
It handles the main system-specific operations, like loading dynamic libraries
for SCF (see section <A HREF="cs_134.html#SEC297">6.4 Shared Class Facility (SCF)</A>). So using it will make most of your application
system-independent.
<P>
<LI>
It tries to find global installations of the Crystal Space run-time libraries.
<P>
<LI>
It provides the input drivers, so you can access mouse, keyboard and
joystick.
<P>
<LI>
It loads and initializes the plug-ins (using SCF) and sends them their
private and broadcast events.
<P>
<LI>
It keeps a log file and provides functions for printing debugging messages,
warnings, and errors.
<P>
<LI>
It keeps track of the application's configuration file and automatically reads
all options required by the system or any plug-in.
<P>
<LI>
It processes the command-line parameters and also allows plug-in modules to
react to the parameters.
<P>
<LI>
It calls additional startup and shutdown functions of some basic plug-in
modules, called the <EM>drivers</EM>.
<P>
<LI>
All these methods are <EM>virtual</EM> methods, so you can override them.
</UL>
<P>
<A NAME="SEC293"></A>
<H3> How to Use the System Driver </H3>
<!--docid::SEC293::-->
<P>
The system driver is explicitly designed to be a superclass for your own system
driver class. In particular, the <CODE>NextFrame()</CODE> and <CODE>HandleEvent()</CODE>
methods are generally overridden by most applications.
</P><P>
The system driver class is named `<SAMP>SysSystemDriver</SAMP>'. This class contains
all system-specific functions. It is, itself, a subclass of
`<SAMP>csSystemDriver</SAMP>', which contains the system-independent stuff.
</P><P>
A typical application would perform the following steps:
</P><P>
<UL>
<LI>
Create an instance of its subclass of `<SAMP>SysSystemDriver</SAMP>'.
<P>
<LI>
Call <CODE>System->Initialize()</CODE>. This will process the command-line, load
and initialize the plug-in modules and open the main configuration file.
<P>
<LI>
Load all application-specific data. You can, of course, load additional stuff
later, but if an error occurs (e.g. an important file is missing), the user
does not have to wait until complete start-up to see this error.
<P>
<LI>
Call <CODE>System->Open()</CODE>. This will <EM>open</EM> the plug-in modules. The
exact meaning of this operation is specific to each plug-in. For instance, a
graphics-related module might change the graphics mode; a sound-related module
might enable sound output; and an input-related module might enable keyboard
processing.
<P>
Any events triggered by these drivers will be sent to your application via the
<CODE>HandleEvent()</CODE> function. If you override this function, you must still
call the old function.
</P><P>
<LI>
Call <CODE>System->Loop()</CODE>. This function will only return when your program
exits the main event loop. Of course you can control when this happens, and
you can restart the loop later, but for most applications exiting the main loop
means exiting the application.
<P>
Once you have entered this loop, the system driver will call the
<CODE>NextFrame()</CODE> method every frame. This happens at irregular time steps,
so you should use the <CODE>GetElapsedTime()</CODE> function to see how much time
has passed.
</P><P>
<LI>
Close and delete the system driver. You don't have to call
<CODE>System->Close()</CODE> explicitly, as this will be done automatically when
you delete the object.
</UL>
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