Hi Fred,
Glad to see someone is starting to nibble at the 8.50 format and figure it
out. If you are developing code that takes the bezier outlines and can turn
that into a polygon representation, then it shouldn't be terribly difficult
to add that into genapts.
For lines and markings, I think the easiest path in the short term will be
to cut those into the surface. However, this can explode the polygon count
and rendering load so we need to be careful, but it should be manageable if
we don't get too crazy with lots of small segments around curves to make
them look perfectly smooth.
I've never played around with glPolygonOffset in the context of btg files
(terragear/genapts) so I don't believe there's any support there. It's
difficult because airport surfaces are curved and are not planar, so most
likely any use of glPolygonOffset will not be perfect and there will be
places where the lines z-fight with the underlying surface ... unless we
really go crazy with a large offset value in which case the lines could
bleed through some of the surfaces when they should be hidden behind them.
Still it might be worth playing around with to see what kind of results are
actually achievable.
I wonder what tricks and approaches the gaming community uses for drawing
clear and realistic roads? The problem with cutting the lines into the
surface as polygons is that (1) you explode the polygon count and (2) you
have hard aliased edges which can become distracting in the distance.
Cooking the lines into the surface texture gets rid of the aliasing problem,
but then you explode your texture memory requirements and need to do a lot
of work to generate those textures on the fly, or generate them once and
store them. And drawing the lines on top using glPolygonOffset is hard to
do well when you are dealing with non-planer surfaces and the visual result
of glPolygonOffset (at least historically) has not been consistent across
different video cards and vendors. It's a difficult challenge to do well.
Regards,
Curt.
On Sun, Jun 14, 2009 at 6:56 AM, Frederic Bouvier wrote:
> Hi,
>
> I committed the support to read new X-Plane 850 file format in
> flightgear. That doesn't mean that airports will look different in
> current scenery because TerraGear tools have not been updated yet, but
> this is the first step to support the format.
>
> Here are two screenshots comparing the ground radar with the different
> data :
> http://frbouvi.free.fr/flightsim/KSBD-810.png
> http://frbouvi.free.fr/flightsim/KSBD-850.png
> The Google Maps link: http://tinyurl.com/n9khev
> You should notice the smooth curves in the 850 screenshot.
>
> The parser should read current data normally, and nobody should see the
> difference until we change the data.
>
> Please shout if you find something broken or overlooked. (actually
> something is broken in the 777 ground radar, but it's not me ;-) )
>
> Curt wrote (about linear features) :
> > Fred, were you thinking of cutting these lines into the surface (with
> > hard polygon edges) or drawing them over the top like with a
> > glPolygonOffset() approach? Or something else? It would be really
> > great to be able to add taxi lines and other markings to our airports.
>
> I didn't really thought about it yet. I am open to ideas. Does the .btg
> file format support the glPolygonOffset approach ?
>
> Regards,
> -Fred
>
> --
> Frédéric Bouvier
> http://my.fotolia.com/frfoto/ Photo gallery
> http://fgsd.sourceforge.net/ FlightGear Scenery Designer
>
>
>
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--
Curtis Olson: http://baron.flightgear.org/~curt/
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