Re: [Flightgear-devel] Rembrandt performance

[Renk T. <tho...@jy...>]

> It could help you to understand why you are getting that poor  
> performances
> with your pretty fast beast  GTX 670M.

Thanks, though I remain mystified.

There are few differences I can spot:

* you have tree density to 0.7 in the shots, I had it at 2.4 - since  there's lots of trees in the scene (it's tropical forest), that would be expected to have an impact

* you have cloud density set to 0.4 whereas I have set it to 1, and also in vaguely remember seeing a bit more clouds

* you have dds textures used, I have used the regional set - my understanding was that this should affect texture loading times and available resolution, but not really runtime performance, but this needs to be checked

-> So I have 4 times the number of trees in the scene and 2-3 times the number of cloud sprites. I'm not completely sure how Rembrandt manages trees, but it could be that since they're semi-transparent they're like the clouds taken out of the deferred rendering approach. Multiple cloud sprites in a row are a significant drain on both vertex and fragment shaders as you may need hundreds of texture lookups - so the available performance for Rembrandt-specific tasks isn't quite the same.

My gut feeling is that this can't account for a factor 4 in framerate though, especially since there is still the pixel number working the opposite way this time - I will have to test this.

In addition there's the question of having two GPUs. I wonder if they're both utilized for the job - if so, maybe one needs such a setup to get above 30 fps with shadows? It would be helpful if a few other Rembrandt users could give some indication of what framerates they usually get and what the main framerate killers are.

* Thorsten