Re: [AD] object oriented AL_SYSTEM

[Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx>]

On Sunday 27 August 2006 1:36 pm, Peter Hull wrote:
> What would the system object be used for? (from the Allegro user's
> point of view)

IMO its not "for" the user. Its to make the internals a little more organized 
and easier to extend.

> There will only be one instance of it (unless we can see a need for
> multiple independent Allegro systems running in the same app?) and it
> shouldn't be a global variable (for DLL/.so linking issues)
>
> Then say we wanted the OS name, the user's code could be
> // Option 1
> const char* os = al_get_os_name();
> or
> // Option 2
> AL_SYSTEM* sys = al_get_system();
> const char* os = sys->os_name;
>
> The former style has more flexibility* but more impact on the namespace.
>
> Pete
>
> * i.e. it can return things that are not just simple properties.
> Writing accessor functions like
> AL_SYSTEM* sys = al_get_system();
> const char* os = al_get_os_name(sys);
> would seem to be unnecessary if there's only one system object -
> option 1 would suffice.
>
> On 8/27/06, Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx> wrote:
> > On Saturday 26 August 2006 4:12 am, Elias Pschernig wrote:
> > > How would a base structure like below look?
> > >
> > > struct AL_SYSTEM_DRIVER
> > > {
> > >    ...variables + methods
> > > };
> > >
> > > struct AL_SYSTEM
> > > {
> > >    AL_SYSTEM_DRIVER *driver;
> > >    ... variables
> > > };
> > >
> > > ... for each driver XXX
> > > struct AL_SYSTEM_XXX
> > > {
> > >    AL_SYSTEM *system;
> > >    ... variables
> > > }
> > >
> > > They would all be internal and no members accessed by the user.
> > >
> > > The first struct would be just like the current SYSTEM_DRIVER - i.e.
> > > the "interface" or "vtable". We didn't decide yet what features we want
> > > from that (there's still
> > > http://awiki.tomasu.org/bin/view/Main/ProposedVTables ).
> > >
> > > The second struct would be an object to hold all the system specific
> > > global variables, e.g. things like the detected CPU capabilities and
> > > whatever else is now in global variables floating around.
> > >
> > > The last struct would be a driver specific version of AL_SYSTEM, which
> > > could be cast to it. It would be created somewhere in al_init,
> > > something like:
> > >
> > > AL_SYSTEM *_al_create_system(AL_SYSTEM_DRIVER *driver)
> > > {
> > >    system = driver->create_system(driver);
> > >    ... initialize platform independent stuff in system
> > >    return system;
> > > }
> > >
> > > And driver->create_system might be:
> > >
> > > AL_SYSTEM *_al_create_system_x11(AL_SYSTEM_DRIVER *driver)
> > > {
> > >    AL_SYSTEM_X11 *system = _AL_MALLOC(sizeof *system);
> > >    ... initialize driver specific stuff in system
> > >    return (AL_SYSTEM *)system;
> > > }
> > >
> > > The advantage I see in it is that we don't need internal global
> > > variables floating around so much. Especially under X11, the _xwin
> > > struct could go into the created AL_SYSTEM_X11 object.
> >
> > I think it should go something like:
> >
> > struct AL_SYSTEM {
> >         ...
> > };
> >
> > struct AL_SYSTEM_FOO {
> >         AL_SYSTEM base;
> > }
> >
> > AL_SYSTEM_FOO can now be cast as a AL_SYSTEM just fine, and AL_SYSTEM_FOO
> > can add anything it wants.
> >
> > --
> > Thomas Fjellstrom
> > tfjellstrom@xxxxxxxxxx
> >
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> > --
> > https://lists.sourceforge.net/lists/listinfo/alleg-developers
>
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> Get stuff done quickly with pre-integrated technology to make your job
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-- 
Thomas Fjellstrom
tfjellstrom@xxxxxxxxxx