Anomalous FPS drop with Terrain shadow

Any issues, problems or troubleshooting topics related to the Prepar3D client application.
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Joined: Mon Jul 24, 2017 4:21 pm

Anomalous FPS drop with Terrain shadow

Postby Rygar79 » Sun Dec 02, 2018 11:23 pm

I have installed P3D 4.4 and found two problems (initially with a clean full install, then also with add-on installed).
Both occurs when Terrain shadow is enabled.
This setting has always been heavy on my system, an i7-5820k + Ati Radeon 390, and I must set it to lowest cast distance with tessellation to low for good performance, but I never had these problems with older P3D versions (didn't tried the v4.3).

Default scenario, but seems to happen almost everywhere.
All details to off/minimum and fps unlimited to better evince the issue.
If I'm over a certain altitude and look up (from cockpit or external camera), the FPS suddenly drops.
See the following HD video in fullscreen and look at the altitude and FPS when the camera is pointing up. Here the FPS drop happens at exactly 795 feet.
If I move trough the scenery the altitude at witch the drop happen can change a lot, maybe it's related to the distance to the ground.

This is unrelated with the previous issue.
When the sun position is low on the horizon, I have an FPS drop when the camera is pointing in the opposite direction from where the sunlight come, regardless of the scenery complexity on that view. This also happen both in external and internal views. See the next video.

I have tried deleting prepar3D.cfg and the shaders, nothing has change.

Lastly, there are some scenery area where I have max 20 FPS even if it is pretty deserts and there are only some trees around, for example departing from USDD.

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Rob McCarthy
Lockheed Martin
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Joined: Wed Aug 24, 2011 1:37 pm

Re: Anomalous FPS drop with Terrain shadow

Postby Rob McCarthy » Tue Dec 04, 2018 7:48 pm


You mentioned not seeing these performance hits on older versions, what version was the most recent that didn't have this issue? Also were you using the same graphics driver with that version of Prepar3D?

Rob McCarthy
Rob McCarthy
Prepar3D® Core Lead

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Joined: Mon Jul 24, 2017 4:21 pm

Re: Anomalous FPS drop with Terrain shadow

Postby Rygar79 » Wed Dec 05, 2018 1:05 pm

Thanks for the response Rob.
Being a long time that I don't use P3D, I don't remember what graphics driver I had installed at that time, neither if the version that i had installed before the upgrade to 4.4 was the 4.1 or 4.2, anyway I never see that slowdown.

Now when I pitch up the aircraft the fps drop. Impossible that I never notice it before.
Apart of the video with details set to low, whit default detail the fps drop under 5.
Also I see that when terrain shadow is enabled the GPU is always towards or at 100%, even with all the others details at minimun like in the video. All this with FPS unlocked.
With fps locked at 30, the gpu is around 30% at default details, the when reaching the drop point it's going down to around 16 and the GPU goes 100%.
It has always been the inverse when looking towards the sky, with an increase in fps and lower gpu usage..

Anyway I did some test:
I tried all the old P3D clients (note: none of these works with the 4.4 content/scenery, it hang on the main screen without loading the F-22 model, then CTD, even after deleting all P3D generated files/folder).
Fortunately I have a 4.0 backup.

The problem is persisting in all versions.

Then I tried with 2 old amd graphics driver, 17.5.2 and 16.10.3, without success.
The only differences is that with the 17.5.2, when reaching the point of the fps drop, this is smaller, then fps gradually decrease as I gain altitude.

Maybe the problem is in my part, and at this point I try with a fresh windows 10 installation.

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Re: Anomalous FPS drop with Terrain shadow

Postby Rygar79 » Fri Dec 07, 2018 5:35 pm

Ok I did a fresh install of Windows 10 from latest ISO, installed the latest AMD drivers, 18.12.1 and a fresh installation of P3D 4.4. The problem persist, there is definitely something wrong.

It seems related with the camera angle towards the sky and with altitude. Note that from tower view there is no FPS drop, because it's under the altitude at wich that appears.

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