Compile error in DeferredDecal.usf

Development Programming & Scripting
1

This being an experimental feature, I don’t know if Epic intends on preserving it. However, it seems that volumetric decals are currently unmaintained: DeferredDecal.usf fails to compile due to FGBufferData Data variable not being fully initialized.

Replacing line:
https://github.com/EpicGames/UnrealEngine/blob/dff3c48be101bb9f84633a733ef79c91c38d9542/Engine/Shaders/DeferredDecal.usf#L369
with FGBufferData Data = (FGBufferData)0; solves the compile error, and the SDF does show up. However, I don’t think it is being lit correctly.

Here’s a basic sample material setup that causes the error with a DeferredDecal → Volumetric Distance Function material. Errors show up when you try to save the material.

Begin Object Class=MaterialGraphNode Name="MaterialGraphNode_0"
   Begin Object Class=EdGraphPin Name="EdGraphPin_4414"
   End Object
   Begin Object Class=MaterialExpressionLightVector Name="MaterialExpressionLightVector_8"
   End Object
   Begin Object Name="EdGraphPin_4414"
      PinName="Output"
      PinFriendlyName=" "
      Direction=EGPD_Output
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_1.EdGraphPin_4416'
   End Object
   Begin Object Name="MaterialExpressionLightVector_8"
      MaterialExpressionEditorX=-608
      MaterialExpressionEditorY=16
      MaterialExpressionGuid=3CFA132449C302EB3BDD0986BFF1DC89
      Material=PreviewMaterial'/Engine/Transient.NewMaterial'
   End Object
   MaterialExpression=MaterialExpressionLightVector'MaterialExpressionLightVector_8'
   Pins(0)=EdGraphPin'EdGraphPin_4414'
   NodePosX=-608
   NodePosY=16
   NodeGuid=EBF746234BAD67BFF8B046BEC87854B3
End Object
Begin Object Class=MaterialGraphNode Name="MaterialGraphNode_1"
   Begin Object Class=EdGraphPin Name="EdGraphPin_4419"
   End Object
   Begin Object Class=EdGraphPin Name="EdGraphPin_4418"
   End Object
   Begin Object Class=EdGraphPin Name="EdGraphPin_4417"
   End Object
   Begin Object Class=EdGraphPin Name="EdGraphPin_4416"
   End Object
   Begin Object Class=MaterialExpressionMaterialFunctionCall Name="MaterialExpressionMaterialFunctionCall_8"
   End Object
   Begin Object Name="EdGraphPin_4419"
      PinName="Result"
      Direction=EGPD_Output
   End Object
   Begin Object Name="EdGraphPin_4418"
      PinName="Radius"
      PinType=(PinCategory="required")
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_3.EdGraphPin_4426'
   End Object
   Begin Object Name="EdGraphPin_4417"
      PinName="Center"
      PinType=(PinCategory="required")
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_2.EdGraphPin_4424'
   End Object
   Begin Object Name="EdGraphPin_4416"
      PinName="UVs"
      PinType=(PinCategory="required")
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_0.EdGraphPin_4414'
   End Object
   Begin Object Name="MaterialExpressionMaterialFunctionCall_8"
      MaterialFunction=MaterialFunction'/Engine/Functions/DistanceFields/Shapes/DistanceField_Sphere.DistanceField_Sphere'
      FunctionInputs(0)=(ExpressionInputId=F8B8E4294601B71325484D8C3615068D,Input=(Expression=MaterialExpressionLightVector'MaterialGraphNode_0.MaterialExpressionLightVector_8',InputName="Coordinates"))
      FunctionInputs(1)=(ExpressionInputId=33A0DD1E4F75D65C1606A0881D5D0838,Input=(Expression=MaterialExpressionConstant3Vector'MaterialGraphNode_2.MaterialExpressionConstant3Vector_14',InputName="Center"))
      FunctionInputs(2)=(ExpressionInputId=F6097B644DE4EB2586DB51AF6933D082,Input=(Expression=MaterialExpressionConstant'MaterialGraphNode_3.MaterialExpressionConstant_8',InputName="Radius"))
      FunctionOutputs(0)=(ExpressionOutputId=E2B2DD6546CAA7F2657C82B21793D079,Output=(OutputName="Result"))
      MaterialExpressionEditorX=-432
      MaterialExpressionEditorY=80
      MaterialExpressionGuid=0BD2F3E34C1057F55CE757A3CAD62479
      Material=PreviewMaterial'/Engine/Transient.NewMaterial'
      Outputs(0)=(OutputName="Result")
   End Object
   MaterialExpression=MaterialExpressionMaterialFunctionCall'MaterialExpressionMaterialFunctionCall_8'
   Pins(0)=EdGraphPin'EdGraphPin_4416'
   Pins(1)=EdGraphPin'EdGraphPin_4417'
   Pins(2)=EdGraphPin'EdGraphPin_4418'
   Pins(3)=EdGraphPin'EdGraphPin_4419'
   NodePosX=-432
   NodePosY=80
   NodeGuid=55823A3340059E27C8AEECA82D554210
End Object
Begin Object Class=MaterialGraphNode Name="MaterialGraphNode_2"
   Begin Object Class=EdGraphPin Name="EdGraphPin_4424"
   End Object
   Begin Object Class=MaterialExpressionConstant3Vector Name="MaterialExpressionConstant3Vector_14"
   End Object
   Begin Object Name="EdGraphPin_4424"
      PinName="Output"
      PinFriendlyName=" "
      Direction=EGPD_Output
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_1.EdGraphPin_4417'
   End Object
   Begin Object Name="MaterialExpressionConstant3Vector_14"
      Constant=(R=0.500000,G=0.500000,B=0.500000,A=0.000000)
      MaterialExpressionEditorX=-624
      MaterialExpressionEditorY=96
      MaterialExpressionGuid=EB3B5BEC43713416E20DE0B6FE8E2789
      Material=PreviewMaterial'/Engine/Transient.NewMaterial'
   End Object
   MaterialExpression=MaterialExpressionConstant3Vector'MaterialExpressionConstant3Vector_14'
   Pins(0)=EdGraphPin'EdGraphPin_4424'
   NodePosX=-624
   NodePosY=96
   NodeGuid=8EE838FC41E539C5D22F01AE776C6F2B
End Object
Begin Object Class=MaterialGraphNode Name="MaterialGraphNode_3"
   Begin Object Class=EdGraphPin Name="EdGraphPin_4426"
   End Object
   Begin Object Class=MaterialExpressionConstant Name="MaterialExpressionConstant_8"
   End Object
   Begin Object Name="EdGraphPin_4426"
      PinName="Output"
      PinFriendlyName=" "
      Direction=EGPD_Output
      LinkedTo(0)=EdGraphPin'MaterialGraphNode_1.EdGraphPin_4418'
   End Object
   Begin Object Name="MaterialExpressionConstant_8"
      R=0.500000
      MaterialExpressionEditorX=-544
      MaterialExpressionEditorY=240
      MaterialExpressionGuid=8949044C42289414BA01CC938309A037
      Material=PreviewMaterial'/Engine/Transient.NewMaterial'
   End Object
   MaterialExpression=MaterialExpressionConstant'MaterialExpressionConstant_8'
   Pins(0)=EdGraphPin'EdGraphPin_4426'
   NodePosX=-544
   NodePosY=240
   NodeGuid=77D141D547A1196BE019E08146379436
End Object
2

Hey num3ric-

Can you provide what the exact compile error is that you’re receiving? Can you also explain the setup you’re using? I used the setup you provided and plugged the DistanceField_Sphere node into base color, however I’m not sure what you are doing from here. Please be as descriptive in your reproduction steps as possible.

3

Here’s a screen capture of the exact material setup and errors (which show up when you save it):

https://dl.dropboxusercontent.com/u/29102565/ue4/volumetricdecalerror.png

Then I’m applying this material to a deferred decal actor in the scene.

4

This is based on this reference fyi: Experimentation: Volumetric Decals - Rendering - Unreal Engine Forums

5

You need to create an Add node and add the Light Vector with a Vector3 node. Then plug the output of your Add node into Coordinates (V3) input. Let me know if this resolves the issue or if you need further assistance.

Cheers,

6

Adding the LightVector with any Vector3? That does not solve the issue no. The uninitialized data error in DeferredDecal.usf remains.

Only with the code fix I mentioned above are signed distance fields rendered.

7

Please take this code fix you have provided and submit a pull request to have this code changed. Reports like this where users have the code that fixes an issue can be submitted via a Pull Request on GitHub. This makes it easier on us as when getting a fix in place as it skips the entire bug reporting process and the necessity for engineers to get a fix.

Let me know if you have further questions or need additional assistance.

Cheers,