Re: [AD] OpenGL

["Robert Ohannessian" <ROhannessian@xxxxxxxxxx>]

>  I would hide any refence to OpenGL and use a dummy `bitmap':

AGL already provides you with this ability (well, to the limited extent
of the vtable entries we implemented).


> -----Original Message-----
> From: alleg-developers-bounces@xxxxxxxxxx [mailto:alleg-
> developers-bounces@xxxxxxxxxx] On Behalf Of Evert Glebbeek
> Sent: Tuesday, July 25, 2006 7:03 AM
> To: Coordination of admins/developers of the game programming library
> Allegro
> Subject: Re: [AD] OpenGL
> 
> On Tuesday 25 July 2006 13:44, Elias Pschernig wrote:
> > Does it seam feasible to somehow merge in all of AllegroGL, just so
we
> > have working OpenGL again in 4.3, and then worry about refining this
to
> > a new graphics driver structure later?
> >
> > Or is it maybe better to start a clean OpenGL driver from scratch?
> >
> > The former probably would be rather messy, but once it compiles,
would
> > mean we get all the features already in AllegroGL. The latter means,
> > we'd initially start with only a minimal implementation, and then
would
> > need to add the required features again step by step (probably
peeking
> > at the AllegroGL code).
> 
> What I would prefer in terms of the graphics drivers is to change the
> existing
> vtables now and adapt the code to use the new drivers.
> The real problem I had with that (which I brought up before and was
> discussed,
> without reaching some final consensus) is that right now, changing the
> graphics drivers will break all other drivers on all other platforms.
Now
> maybe we should just Not Care and allow things to break and then fix
them
> later.
> 
> > What I expect in the end is, that I simply can do:
> >
> > display = al_create_display(640, 480, AL_AUTODETECT, AL_OPENGL);
> > glClearColor(0, 0, 1, 1);
> > glClear();
> > al_flip_display(display);
> 
> I would hide any refence to OpenGL and use a dummy `bitmap':
> 
> display = al_create_display(..., AL_ACCELERATED, ...);
> bmp = al_get_buffer(display);
> al_clear_bitmap(bmp, 0,0,1,1); // or whatever colour format
> al_flip_display(display);
> 
> that way, code can be written with complete ignorance of the
underlying
> driver
> and work properly. Sure, one can still use the normal OpenGL commands
(and
> we
> must make sure that this does work), but the second example should
work
> too.
> 
> In case of OpenGL, the returned bitmap from al_get_buffer could just
have
> a
> flag set to say `use OpenGL commands instead of drawing to me', or
better
> yet, the drawing operations in the vtable could be directly mapped to
> OpenGL
> commands:
> 
> al_clear_bitmap(bmp, ...) gets translated to
> bmp->vtable->clear(bmp, ...);
> which is a reference to
> al_opengl_clear_bmp(BITMAP *dummy, ...)
> {
>    glClearColor(...);
>    glClear();
> }
> 
> > Each graphics driver would have a capability flag telling if it can
> > provide an OpenGL context or not. And graphics drivers would see in
> > their initialization function if OpenGL is requested, and initialize
an
> > OpenGL context if so.
> 
> I think a generic AL_ACCELERATED flag would be better. Internally it
would
> work as you describe anyway.
> 
> Evert
> 
>
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