FStaticPrimitiveDrawInterface::DrawMesh draws only 2 polygons

Development Programming & Scripting
1

I am trying to draw 4 polygons(4 triangles). For this point I am using a component implemented from PrimitiveComponent and own SceneProxy.
So:

FHexagonSceneProxy::FHexagonSceneProxy(const UHexagonHUDComponent* InComponent)
	: FPrimitiveSceneProxy(InComponent)
{
	auto  NonConstInComponent = const_cast<UHexagonHUDComponent*>(InComponent);
	thickness = NonConstInComponent->GetThickness();
	radius = NonConstInComponent->GetRadius();
	b_only_outline = NonConstInComponent->IsOutLineOnly();
	std::tie(main_color, outline_color) = NonConstInComponent->GetColor();
	MaterialInterface = NonConstInComponent->GetMaterial(0);
	if (NonConstInComponent->IsXRay()) {
//		Doesn't work
//		depth = SDPG_Foreground;
		bOccluded = true;
	}
	if (!b_only_outline) {
		const float delta_rad = 1.047198f;
		VertexBuffer.Vertices.SetNumUninitialized(6);
		IndexBuffer.Indices16.SetNumUninitialized(12);
		//Initialize Vertices
		{
			float angle_one = 0;
			for (int i = 0; i < 6; i++) {
				FVector start_pos = FVector::ZeroVector;
				//Calculate first point of the line
				start_pos.X += cosf(angle_one) * radius;
				start_pos.Y += sinf(angle_one) * radius;
				angle_one += delta_rad;
				VertexBuffer.Vertices[i].Position = start_pos;
				VertexBuffer.Vertices[i].TangentX = FVector(0);
				VertexBuffer.Vertices[i].TangentZ = FVector(0);
				VertexBuffer.Vertices[i].TextureCoordinate = FVector2D(start_pos.X, start_pos.Y);
			}
		}
		//Initialize Index Buffer
		{
			IndexBuffer.Indices16[0] = 0;
			IndexBuffer.Indices16[1] = 1;
			IndexBuffer.Indices16[2] = 2;

			IndexBuffer.Indices16[3] = 5;
			IndexBuffer.Indices16[4] = 4;
			IndexBuffer.Indices16[5] = 3;

			IndexBuffer.Indices16[6] = 5;
			IndexBuffer.Indices16[7] = 0;
			IndexBuffer.Indices16[8] = 3;

			IndexBuffer.Indices16[9] = 2;
			IndexBuffer.Indices16[10] = 0;
			IndexBuffer.Indices16[11] = 3;
		}
		InitResources();
	}
}

void FHexagonSceneProxy::MakeMeshBatch(FMeshBatch& Mesh) const
{

	FMaterialRenderProxy * MaterialProxy = MaterialInterface->GetRenderProxy(IsSelected());//MaterialInstance->GetRenderProxy(IsSelected());

 	FMeshBatchElement& BatchElement = Mesh.Elements[0];
	BatchElement.IndexBuffer = &IndexBuffer;
	Mesh.bWireframe = false;
	Mesh.VertexFactory = &VertexFactory;
	Mesh.MaterialRenderProxy = MaterialProxy;
	Mesh.CastShadow = true;
	BatchElement.PrimitiveUniformBuffer = CreatePrimitiveUniformBufferImmediate(GetLocalToWorld(), GetBounds(), GetLocalBounds(), true, UseEditorDepthTest());
	BatchElement.FirstIndex = 0;
	const int IndexCount = FMath::Max(IndexBuffer.Indices16.Num(), IndexBuffer.Indices32.Num());
	BatchElement.NumPrimitives = IndexCount / 3;
	BatchElement.MinVertexIndex = 0;
	BatchElement.MaxVertexIndex = VertexBuffer.Vertices.Num() - 1;
	Mesh.ReverseCulling = IsLocalToWorldDeterminantNegative();
	Mesh.Type = PT_TriangleList;
	Mesh.DepthPriorityGroup = SDPG_World;
}

void FHexagonSceneProxy::DrawStaticElements(class FStaticPrimitiveDrawInterface* PDI)
{
	const float ScreenSize = 1.0f;

	FMeshBatch MeshBatch;
	MakeMeshBatch(MeshBatch);
	PDI->DrawMesh(MeshBatch, ScreenSize);
}

However I have 6 Vertices and 12 Indexies at the game I see only 2 polygons. I have to skip much code to make it more readable. What can be the reason of it?

2

Did you check the value of Indexcount?
And simple question, did you turn around you drawing, if the triangles are not draw both side, it might be there but invisible from one point of view.

3

I found the solution
The index buffer must look like this

		    IndexBuffer.Indices16[0] = 2;
			IndexBuffer.Indices16[1] = 1;
			IndexBuffer.Indices16[2] = 0;

			IndexBuffer.Indices16[3] = 3;
			IndexBuffer.Indices16[4] = 2;
			IndexBuffer.Indices16[5] = 0;

			IndexBuffer.Indices16[6] = 5;
			IndexBuffer.Indices16[7] = 3;
			IndexBuffer.Indices16[8] = 0;

			IndexBuffer.Indices16[9] = 5;
			IndexBuffer.Indices16[10] = 4;
            IndexBuffer.Indices16[11] = 3;

As I understand, the first index of the triangle must be the biggest one, second smaller, third the smallest one.

4

ok, I think it is more the positions of the points and not really the index that count. The triangle must be created in clockwise order to see it from your point of view. Like in basic opengl:
https://www.khronos.org/opengl/wiki/Face_Culling