Paul Surgeon wrote:

I played around with some runway lighting today to see if textured polygons are feasible.
Here is what textured, billboard runway lights look like :
http://surgdom.hollosite.com/flightgear/screenshots/index.html


With 6 * 10000 ft runways all in view at one time my frame rate dropped from 50 down to 20 FPS on an old Ti 4200.
I think 6 * 10000 ft runways should pretty much cater for any large airport.
That's close to 5000 runway lights.


This is just a hardcoded test to see what the performance impact is if one uses a brute force approach with zero performance enhancements.
One could probably cull in between lights beyond certain distances which would help performance and look a bit better from a distance.


Also I'm not sure what sort of impact billboarding and distance scaling has on performance - it would probably be faster if I had fixed polygons.

If my Ti4200 can do the job then I'm sure newer video cards like the nVidia FX 5700 and up should handle these lights quite nicely.



One thing we would need to figure out before we could head down this path would be a way to hide runway lights that are viewed from behind. Approach and runway lights are directional and pointed directly at aircraft arriving on the glide slope. So as you view them off axis they will be dimmer and when viewed from behind you shouldn't see them at all.


Currently lights are actually a triangle drawn in "point" mode with two of the verticies set to zero alpha. This way backface culling hides the lights from behind.

But if we switch to some sort of billboarded quad for lights, we lose this capability.

We would either need to come up with some clever trick, write a new ssg selector node with this sort of functionality, or use vertex shaders which plib doesn't support.

Any ideas?

Curt.

--
Curtis Olson        http://www.flightgear.org/~curt
HumanFIRST Program  http://www.humanfirst.umn.edu/
FlightGear Project  http://www.flightgear.org
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