#2382 Vegetation transparency not working in compositor if AA is on

[Lauri Uusitalo]

Hi,

This is my first bug report here, so appoligies for any errors.

On ubuntu with Amd gpu, running version 2020.03.00 with compositor, all vegetation is shown in a black (or green) square if anti-aliasing is on. Tested both with low-spec and als. Changing shader options has no effect, neither does disabling vegetation shadows.

On version 2020.01 without compositor vegetation work as expected.

Version: Fgfs 2020.03.00, Simgear 2020.03.00, OSG 3.6.5
system: ubuntu 20.04, 5.4.0-48-lowlatency
gpu: Amd rx vega 56
driver: Mesa 20.3.0-devel
startup settings used (though removing/changing these has no effect):
--launcher
--compositor=Compositor/als
--disable-ai-traffic
--prop:/sim/rendering/multithreading-mode=AutomaticSelection
--prop:bool:/sim/rendering/als/shadows/enabled=true
--prop:int:/sim/rendering/als/shadows/sun-atlas-size=2048

attachements: fgfs.log

[Fernando García Liñán]

Hi Lauri,

Did you use these cmd options to enable anti-aliasing?
--prop:/sim/rendering/multi-sample-buffers=true
--prop:/sim/rendering/multi-samples=4

If so, does the issue persist on the ALS pipeline if you remove those cmd options? The ALS pipeline already includes 4x MSAA by default.

[Lauri Uusitalo]

Hi,

I only used qt-launchers option for aa. I did some new testing today, and actually the AA is not working at all, even with commandline options that you gave in your post. However 2020.03.00 without compositor works as it should. Attached is a series of screenshots of the test. I hope that it's good enough to show the issue.

First I run 2020.03.00 without compositor, to establish a baseline for comparison. Only commands used were --launcher and --prop:/sim/rendering/vsync-enable=false.

• Version 2020.03.00 without compositor, launcher option 4x AA. Result: everything works as it should.
• Version 2020.03.00 without compositor, launcher option AA=off. Result: works as expected, no AA and bit uglier trees.

After this I made the following tests. Added command --compositor=Compositor/als :

1: Version 2020.03.00 compositor enabled, launcher option 4x AA. Result: no AA and trees in a black box
2: Version 2020.03.00 compositor enabled, launcher option AA=off. Result: works as expected, no AA and bit uglier trees.
3: Version 2020.03.00 compositor enabled, launcher option AA=off, commandline options --prop:/sim/rendering/multi-sample-buffers=true and --prop:/sim/rendering/multi-samples=4. Result: like test 1, no AA and trees in a box.

1. Version 2020.03.00 compositor enabled, launcher option 4x AA, commandline options --prop:/sim/rendering/multi-sample-buffers=true and --prop:/sim/rendering/multi-samples=4. Result: like test 1 and 3, no AA and trees in a box.

As a side note: I have also tested this with AMDGPU-PRO driver (AMD:s proprietary driver) and AA works as expected. So this seems to be an driver issue. Maybe something in how the driver is called by compositor vs. regular ALS pipeline?

Hopefully this helps.

Br
Lauri Uusitalo

[Fernando García Liñán]

Thanks a lot for the very insightful report! The Mesa drivers were being picky about doing MSAA with a depth buffer attached. This has been fixed on my fork and should reach upstream soon.

[Lauri Uusitalo]

Hi,

great that this was helpfull and that you were able to solve the issue.

br
Lauri