Community Tutorial: Local Height Fog in Unreal 5

General Tutorial & Course Discussions
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We can now create Local Height Fog in our scene without the need of an Exponential Height Fog Actor. In this tutorial we will go through this new feature which has been introduced in Unreal 5.3. This is very easy to setup and a nice addition to the large arsenal of features within the engine.

https://dev.epicgames.com/community/learning/tutorials/6B6K/unreal-engine-local-height-fog-in-unreal-5

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Hi,
We found this component will crash the editor when you place it in a complex scene; it seems it causes a memory leak or something, you can reproduce it, place enough local height fog in your scene(45 or more) until it crashes, hope unreal can fix that in next update.

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0xffffffffffffffff

UnrealEditor_RHI
UnrealEditor_RHI
UnrealEditor_RHI
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_RenderCore
UnrealEditor_Core
UnrealEditor_Core
kernel32
ntdll

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Hmm, interesting. If the Local height fog has some issue hopefully they will fix it eventually. You can mention it as a bug report with the details.

For your requirement, if you need that much coverage of volumetric fog in your scene, I would suggest you can use the volume fog material with particles or meshes and scatter them as needed. It will also help to art direct the fog.

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Thank you for your reply :grinning:, in our case, we use one local height fog in the scene, but still, the crashes are almost random, so I found a way to trigger it. thank your suggestion and I will try it!

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Hi, does the local height fog get affected by point lights?
If i try to move a point light near the local height fog it doesn’t seem to get affected, it only works with directional light.
I am pretty new at this so i might be missing something.

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I have found this as well. Having several of the local heightfog actors in the scene increases the frequency of the crashes

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yes it only gets affected by directional light at the moment and not with point lights or spotlights.

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Having multiple of local height fog actors does seem to crash the scene specially when motion blur is on. Can you check with motion blur value 0 in post process volume and see if it is crashing or not.

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Our colleague fixed that issue. It’s a type conversion error in its code that caused the crash. I’m not a programmer, so I can’t tell you how to fix that:(
They reported this bug and hopefully this will be resolved soon.

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10

Oh great, thanks for sharing the update.

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For those that don’t want to wait, I’m guessing this is the issue -

Out.LocalHeightFogCenterPos = (FVector*)GraphBuilder.Alloc(sizeof(FVector3f) * Out.LocalHeightFogInstanceCount, 16);

FVector uses doubles and FVector3f uses floats. I’ve not tried this myself yet but am going to give it a go.

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Same issue using 5.3.2 with Lumen.

Once I place 1-2 local height fogs in the scene the editor eventually crashes with the same error.

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I can confirm this was the issue and also that Epic seem to have fixed it in 5.4.0

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It is crashing the engine for me as well. Just around 4-5 of local height fog actors and it crashes. The error given is memory failure - 0xc0000005. That’s on UE 5.3.2.

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Exactly the same for me in 5.3.2.
120fps then instant crash with the same error message.
The more local height fogs, the most frequent crashes are.

I’m glad to hear that it was fixed in 5.4 !

Unfortunately I’m using some assets that don’t translate well to 5.4 so I must stay on the 5.3.

Did anyone find a solution ?