As many are finding out, Prepar3D (P3D) version 2.3 has an updated cloud rendering system at work. Most of that work comes from the cloud.fx file, which is located in your installation directory in the “ShadersHLSL” file.
This issue is widely discussed on both the Lockheed Martin ums AVSIM. From doing some reading there the following has been concluded (to this point). Version 2.3’s cloud system that involves the cloud.fx has extra “features” shadows (clouds casting shadows on the ground) in version 2.3, as well as methods to give them more volume, called volumizing.
my system, this resulted in a major penalty in weather conditions that had a thick cloud layer (or more). In some cases 15-20 fps of a decrease. Some people have reported good success in mitigating this issue by just eliminating the volumizing part of cloud.fx, though in my case it only saved about 2 fps.
The volumize mod is done by editing the cloud.fx file in the ShadersHLSL… (advise making a copy of cloud.fx to say cloud.fx.old first)
Simply place two slashes in front of the line as follows (edit cloud.fx in notepad): //#define VOLUMIZE
The alternative fix involves replacing the entire cloud.fx in version 2.3 (after saving a copy) with a copy from version 2.2.
**in all cases, any mods done to files in ShadersHLSL require that you delete or rename the Prepar3D V2 folder in your users~\username\appdata\local\lockheed martin folder once the change is made bee you launch P3D.
In the gif animation below I have 3 examples.. All 3 do not have any addons installed, just the base P3D install. These tests were on a different “test” system than my typical setup. This test was using a midstream Gece 650ti, whereas my home system i am using a 780ti. In the test below I have the cloud distance set to 70nm high the cloud coverage. Take a look at the results below decide if removing cloud shadows is worth a permance saving.
Note that there are other ways to trim (gain) some FPS.. If you use Active Sky Next (ASN), you could limit the cloud layers to 2 layers. You could try tweaking big frame rate killers in the simulation, such as eliminating shadows from buildings (if you have this set), reducing building autogen or vegetation other tweaks.
Here is a full size link of the gif animation below.
UPDATE: There was a tweak revealed to gain back the permance with version 2.3 of the cloud.fx file, you can find that here.