How to make UProceduralMeshComponent with bDoubleSidedGeometry=true?

MarioCanFly · July 23, 2021, 4:40am

I need to use UProceduralMeshComponent to create the mesh I want. But I need doubleSided collision.

pmc = CreateDefaultSubobject<UProceduralMeshComponent>("pmc");

//Omit the steps：create  Verties, Triangles, Normals, UV, VertexColors, Tangents

pmc->GetBodySetup()->bDoubleSidedGeometry = true;
pmc->CreateMeshSection(0, Verties, Triangles, Normals, UV, UV, UV, UV, VertexColors, Tangents, true);
pmc->SetMaterial(0, MeshMaterial);

This doesn’t work. Can someone please help me?

SiggiG · July 23, 2021, 6:59am

You can create flipped polygons, or if you just need it to render from both sides you can set a flag in your material.

I also have a (pretty old by now) examples for how to build geometry in code, which includes double sided geometry. This uses an alternative to ProceduralMeshComponent called the RuntimeMeshComponent:

github.com

SiggiG/ProceduralMeshDemos/blob/master/Plugins/ProceduralMeshes/Source/ProceduralMeshes/Private/SimpleCylinderActor.cpp

// Copyright Sigurdur Gunnarsson. All Rights Reserved. 
// Licensed under the MIT License. See LICENSE file in the project root for full license information. 
// Example cylinder mesh

#include "SimpleCylinderActor.h"
#include "Providers/RuntimeMeshProviderStatic.h"

ASimpleCylinderActor::ASimpleCylinderActor()
{
	PrimaryActorTick.bCanEverTick = false;
	StaticProvider = CreateDefaultSubobject<URuntimeMeshProviderStatic>(TEXT("RuntimeMeshProvider-Static"));
	StaticProvider->SetShouldSerializeMeshData(false);
}

void ASimpleCylinderActor::OnConstruction(const FTransform& Transform)
{
	Super::OnConstruction(Transform);
	GenerateMesh();
}

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MarioCanFly · July 24, 2021, 2:23am

It’s not difficult to create flipped polygons, but it will cost 2x triangles…
I already make the material double-sided.
I noticed that there is a parameter “Double Sided Geometry” in blueprint of collision box, which is effective. But the actor is made by c++ which cannot open its blueprint.
The document says that the UBodySetup contains the parameter “bDoubleSidedGeometry”, but I don’t know how to use it.