"Accurate Velocities from Vertex Deformation" crashes in Lightmap Density viewmode

“Accurate Velocities from Vertex Deformation” crashes the engine whenever I turn on the Lightmap Density viewmode. The crash is instantaneous, and doesn’t seem to report anything in the logs or crash reporter when it happens. If I don’t use the Lightmap Density viewmode, the feature seems to work just fine. The bug happens in both the launcher binary build of 4.9.1 and the github version of it.

Hi Daniel,

Can you provide more information on what you’re setup is and how you’re able to reproduce this crash? Any steps for what you’re doing before the crash that causes this or a sample project that does this would help as well.

When the editor crashes, is there any Windows error windows that pop up as well? If so, this may be a crash within Windows. Follow the instructions here for the Windows Event Viewer to see there is an error log that may be useful.

Also, please attach your DxDiag here as well.

Thank you!


The setup is a relatively fresh install of Windows 10, and the crash occurs when using DX11 mode (haven’t tried it with DX12 as of yet). It also doesn’t only occur on my specific computer, a friend I’m working with is suffering from the same problem. The problem occurs on any project I open, from the Infiltrator demo all the way to the Blueprint example with the single tree, hallway, cameras, etc.

To reproduce the crash:

Start 4.9 in DX11 mode
Open a project
In the rendering settings for the project, enable “Accurate Velocies from Vertex Deformation”
Restart the editor
Open the project
Enable the Lightmap Density viewmode

In the event viewer, I found this which might help:

Faulting application name: UE4Editor.exe, version:, time stamp: 0x56094ebc
Faulting module name: KERNELBASE.dll, version: 10.0.10240.16384, time stamp: 0x559f38c3
Exception code: 0xc000041d
Fault offset: 0x000000000002a1c8
Faulting process id: 0x47d8
Faulting application start time: 0x01d0fbaf79008bbc
Faulting application path: E:\Program Files\Epic Games\4.9\Engine\Binaries\Win64\UE4Editor.exe
Faulting module path: C:\WINDOWS\system32\KERNELBASE.dll
Report Id: 06eb42dd-8386-4c0f-93e5-03f73e93fa2b
Faulting package full name:
Faulting package-relative application ID:

Aside from the report id, the other fields seem to be consistent between every crash.


Hi Daniel,

Apologies for the delay. I was able to reproduce this and have reported it with UE-22214. Once there is an update I’ll post back here to let you know. This is currently still occurring in our latest 4.10 Preview releases that we’ve released as well.