[Opengc-devel] ogcDataSource.h comments requested

[Damion S. <dam...@ho...>]

Hi everyone,

I've begun preliminary modifications on the ogcDataSource base class to 
provide the generic ability to get and set values of variables. To clarify 
the distinction:

Old model: all variables are public, access to them is not controlled, 
writing to flight model is impossible

New model: all variables are protected, access to them occurs with Get/Set 
functions. Writing to flight model occurs with appropriate Set call.

To this end I've started putting together compiler macros (defined at the 
beginning of ogcDataSource.h) which automatically generate the approprate 
Get/Set functions and member variables from a one-line declaration. This 
saves you time in coding and makes the header easier to read. I also changed 
the documentation style, so that the declaration of a single variable now 
looks like:

/** The number of cows being transported */
ogcDataReadMacro(Num_Cows_In_Baggage, int);

Note that ogcDataReadMacro does not generate a Set() function; it's intended 
for variables which are "read-only" as far as the flight model is concerned. 
Most variables stored in the data source fall into this category.

The other macro is ogcDataReadWriteMacro, which generates a Set function 
that in its default implementation does nothing and should be overridden in 
a derived class to add specific functionality. Variables which can be 
written include commanded control surface deflections (for autopilots), nav 
radio settings, etc.

As of right now, these updates do not affect existing code in any way. 
Although the eventual intent is to have all data members be protected 
members of the class, they are currently still public to maintain 
compatibility with existing code. At some point, once the initial conversion 
is finished, I'll notify the list that we should start converting over 
gauges, components, and any other code that accesses data sources to the 
Get/Set model. In most cases the change will be from:

localCopy = m_pDataSource->Variable_Name

to

localCopy = m_pDataSource->GetVariable_Name();

so I don't anticipate that this will be a major problem. If you want to 
start doing this early, great. If not, that's fine too. Not all of the 
members of the data source class support Get() operations yet, only those 
defined using macros. I will have to add additional macros to handle strings 
and arrays of values (for the engines) and haven't done this yet.

To summarize, what you should do now:

1) Look over the header file. Tell me what you like/dislike. Now's the time 
to complain if it doesn't meet your needs.
2) Begin converting your code to the Get() model, if possible (not yet 
possible for engines or autopilot code).
3) Feedback! The data source class is central to OpenGC and it's important 
that it's up to the job.

Cheers,
-Damion-

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