How does FVertexFactoryInput works?


I’m trying to create my vertex factory and currently I have a problem, that d3dDevice can’t create InputLayout. I have a very informative d3d error:


Ok, I need to specify layout somehow. I’m opening LocalVertexFactory.usf and see this:

struct FVertexFactoryInput
	float4	Position	: ATTRIBUTE0;
	half3	TangentX	: ATTRIBUTE1;
	// TangentZ.w contains sign of tangent basis determinant
	half4	TangentZ	: ATTRIBUTE2;
	half4	Color		: ATTRIBUTE3;

// + a lot of other attributes

Next, I’m opening FStaticMeshLODResources::InitVertexFactory:

Data.PositionComponent = FVertexStreamComponent(
			Data.TangentBasisComponents[0] = FVertexStreamComponent(
			Data.TangentBasisComponents[1] = FVertexStreamComponent(

And here my questions:

  1. Why Position attribute in *.usf have float4 type, and here - on params initialization it have VET_Float3 type? How does it work?
  2. In *.usf there’s a Color attribute, but in params initialization it absent. Why the code works?
  3. Who initialize other parameters?

Huge thanks to . He answered my questions and the answers are:

  1. Need to run with -d3ddebug in order to set debug flag to device. Now I have informative errors descriptions.
  2. float3 to float4 conversion is automatic for position elements, so thats why its defined as a float3 in code and float4 in the shader, And of course it’s legal to use VET_Float4 for initialization.
  3. this Data.PositionComponent = FVertexStreamComponent actually says which field in vertex structure points to which field in the stream. The actual binding of *.usf and code fields are done, for example, in FLocalVertexFactory::InitRHI - attribute index is plays main role.
  4. Similar way other attributes initialized in appropriate classes. In FInstancedStaticMeshVertexFactory::InitRHI, for example.