Description

If you import a static mesh with no setup lightmap and uncheck the option for Generate lightmap UV so that only the UV Channel 0 is present. When you use the Merge Actor tool with a single one of these actors or multiple of this actor with only a single UV the merged asset will save with no geometry leaving it corrupted.

There is a test asset attached and an image of the merged mesh from the static mesh editor.

Steps to Reproduce

1. Import a Static Mesh without a setup Lightmap UV (uncheck from the import option for generate lightmap UV)
2. Drag the actor into the world and make multiple if needed.
3. Open the Merge Actor tool and select these meshes.
4. Leave default settings and click Merge.
5. Open the merged Actor
6. Click on the UV, Normals, Tangents, or any button that is tied directly to the mesh from the toolbar.

Results: This is a corrupted mesh that is generated with no data.

Callstack

MachineId:7D8A1A304BE9658328C158A3D14CC774
EpicAccountId:fb379e8f24784ff699eadd8655f07aef

Assertion failed: (Index >= 0) & (Index < ArrayNum) [Link Removed] [Line: 634]
Array index out of bounds: 0 from an array of size 0

UE4Editor_Core!FDebug::AssertFailed() [d:\builds\ue4_main\engine\source\runtime\core\private\misc\assertionmacros.cpp:332]
UE4Editor_Engine!DrawUVs() [d:\builds\ue4_main\engine\source\runtime\engine\private\primitivedrawingutils.cpp:1689]
UE4Editor_StaticMeshEditor!FStaticMeshEditorViewportClient::DrawUVsForMesh() [d:\builds\ue4_main\engine\source\editor\staticmesheditor\private\staticmesheditorviewportclient.cpp:837]
UE4Editor_StaticMeshEditor!FStaticMeshEditorViewportClient::DrawCanvas() [d:\builds\ue4_main\engine\source\editor\staticmesheditor\private\staticmesheditorviewportclient.cpp:825]
UE4Editor_UnrealEd!FEditorViewportClient::Draw() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorviewportclient.cpp:3361]
UE4Editor_Engine!FViewport::Draw() [d:\builds\ue4_main\engine\source\runtime\engine\private\unrealclient.cpp:1163]
UE4Editor_UnrealEd!UEditorEngine::UpdateSingleViewportClient() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorengine.cpp:1788]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\builds\ue4_main\engine\source\editor\unrealed\private\editorengine.cpp:1564]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\builds\ue4_main\engine\source\editor\unrealed\private\unrealedengine.cpp:371]
UE4Editor!FEngineLoop::Tick() [d:\builds\ue4_main\engine\source\runtime\launch\private\launchengineloop.cpp:2855]
UE4Editor!GuardedMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\launch.cpp:152]
UE4Editor!GuardedMainWrapper() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() [d:\builds\ue4_main\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264]
kernel32
ntdll

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Fixed
ComponentGameplay
Affects Versions4.134.144.15
Target Fix4.15
Fix Commit3198141
Main Commit3198987
CreatedNov 11, 2016
ResolvedNov 15, 2016
UpdatedApr 27, 2018