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optimizing random trees: strong effect on performance ?

An exciting "new" option in FlightGear, that includes reflections, lightmaps, the particle system etc.. A lot is yet to be discovered/implemented!

Re: optimizing random trees: strong effect on performance ?

Postby Thorsten » Mon Nov 23, 2015 12:53 pm

up to 2km use the current scheme
beyond that use single textured quads always facing the camera, no effects like moving and shadows.


That should give you an idea of what perf improvement to expect and whether there is mileage in it.


Not enough I suspect.

Anyway - that's fairly similar to what my old code did, except for the 'replace four crosses by a single quad showing four trees' (getting rid of another 75% of the remaining quads...) - so I know how to do it. Should I try to dig up that code for you?

I guess it's best to let the shader decide not to render the other two.


Yes - you catch it early on and simply move it out of the view frustrum before determining light or fog.
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Re: optimizing random trees: strong effect on performance ?

Postby erik » Mon Nov 23, 2015 1:07 pm

Problem I see is that it still requires the transformation for all quads. If that part could be moved to the shaders it might have an impact.

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Re: optimizing random trees: strong effect on performance ?

Postby Thorsten » Mon Nov 23, 2015 1:12 pm

Sorry what transformation? The billboarding? That's easy to do in the vertex shader.
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Re: optimizing random trees: strong effect on performance ?

Postby erik » Mon Nov 23, 2015 1:16 pm

Sorry, I see the trees only get transformed once at creation time. After that the whole forest is processed as one single object. I thought trees got transformed every frame.

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Re: optimizing random trees: strong effect on performance ?

Postby Richard » Sat Dec 19, 2015 11:26 am

I've been pondering and researching the various methods. What looks promising is instancing at the shader level.

http://3dcgtutorials.blogspot.fr/2013/0 ... graph.html
https://github.com/MPursche/3dcgtutorials
http://trac.openscenegraph.org/projects ... winstanced

This also looks like it might be promising. http://image.diku.dk/projects/media/tru ... ing.08.pdf

It's also lead me onto wonder if instancing could be generally useful (as we have a quite a lot of items in the scenery that are the same model); but to be honest I've not really got enough of a clue how the culling would work.
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Re: optimizing random trees: strong effect on performance ?

Postby Hooray » Sun Dec 20, 2015 12:11 am

Richard wrote in Sat Dec 19, 2015 11:26 am:It's also lead me onto wonder if instancing could be generally useful (as we have a quite a lot of items in the scenery that are the same model)


I agree, even though we don't need to make this specific to just "scenery", but could instead look at the whole scene - even just the 2D use-case has seen quite a bit of discussion over the years (especially in the context of MFDs and complex cockpits), so that it would indeed be useful to consider adding SimGear-level support for instancing: http://wiki.flightgear.org/Canvas_Devel ... Instancing
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Re: optimizing random trees: strong effect on performance ?

Postby vnts » Sat Feb 10, 2018 12:41 am

Not sure if just me: Trees ultra setting+shadow: RAM usage steady blow out.

Happens since introduction of setting. (test: flying about very low. Near PHNL/ENBR/EDDI. Happens at lowish LOD:3000/4000/18000. Slow helis, faster UFO. Various win nightlies.). Seemed strange(?): at very high setting: only 2GB-ish or less. Changing settings back and reloading scenery seems to reset RAM usage. Just normal for sheer amount of trees? Cache/slow clean up of tree data structures (maybe based on bare LOD, and not lower)? If not just me, or a bug, perhaps RAM usage/LOD warning for setting is appropriate(?).

Kind Regards, vnts
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