[TIL]25-01-03

까먹지 않으려고 적어놓음..!

void UMeshProcessor::OffsetUVs(UStaticMesh* StaticMesh, int32 TargetMaterialID, float UVRangeOffset, int32 UVChannel)
{
    if (!StaticMesh || !StaticMesh->GetRenderData())
    {
        UE_LOG(LogTemp, Warning, TEXT("Invalid Static Mesh or no Render Data available"));
        return;
    }

    FStaticMeshRenderData* RenderData = StaticMesh->GetRenderData();
    FStaticMeshLODResources& LODResources = RenderData->LODResources[0];

    const FStaticMeshSectionArray& Sections = LODResources.Sections;

    // Material ID 검증
    if (TargetMaterialID <= 0 || TargetMaterialID > Sections.Num())
    {
        UE_LOG(LogTemp, Warning, TEXT("Invalid Material ID"));
        UE_LOG(LogTemp, Warning, TEXT("MaterialID: %d"), TargetMaterialID);
        UE_LOG(LogTemp, Warning, TEXT("Sections.Num(): %d"), Sections.Num());
        return;
    }

    // Target Material ID에 해당하는 섹션 선택
    const FStaticMeshSection& TargetSection = Sections[TargetMaterialID - 1];
    FStaticMeshVertexBuffers& VertexBuffers = LODResources.VertexBuffers;

    // UV Offset 계산
    float MaterialOffsetX = (TargetMaterialID - 1) * UVRangeOffset;
    UE_LOG(LogTemp, Log, TEXT("MaterialOffsetX for MaterialID %d: %f"), TargetMaterialID, MaterialOffsetX);

    // 중복 정점 추적
    TSet<uint32> ModifiedVertices;

    // 특정 Material ID에 속하는 Vertex만 UV 이동
    for (uint32 TriangleIndex = 0; TriangleIndex < TargetSection.NumTriangles; ++TriangleIndex)
    {
        uint32 BaseIndex = TargetSection.FirstIndex + TriangleIndex * 3;

        uint32 Index0 = LODResources.IndexBuffer.GetIndex(BaseIndex);
        uint32 Index1 = LODResources.IndexBuffer.GetIndex(BaseIndex + 1);
        uint32 Index2 = LODResources.IndexBuffer.GetIndex(BaseIndex + 2);

        // Index 0
        if (!ModifiedVertices.Contains(Index0))
        {
            FVector2f UV0 = VertexBuffers.StaticMeshVertexBuffer.GetVertexUV(Index0, UVChannel);
            UV0.X += MaterialOffsetX; // Apply offset
            VertexBuffers.StaticMeshVertexBuffer.SetVertexUV(Index0, UVChannel, UV0);
            ModifiedVertices.Add(Index0);
        }

        // Index 1
        if (!ModifiedVertices.Contains(Index1))
        {
            FVector2f UV1 = VertexBuffers.StaticMeshVertexBuffer.GetVertexUV(Index1, UVChannel);
            UV1.X += MaterialOffsetX; // Apply offset
            VertexBuffers.StaticMeshVertexBuffer.SetVertexUV(Index1, UVChannel, UV1);
            ModifiedVertices.Add(Index1);
        }

        // Index 2
        if (!ModifiedVertices.Contains(Index2))
        {
            FVector2f UV2 = VertexBuffers.StaticMeshVertexBuffer.GetVertexUV(Index2, UVChannel);
            UV2.X += MaterialOffsetX; // Apply offset
            VertexBuffers.StaticMeshVertexBuffer.SetVertexUV(Index2, UVChannel, UV2);
            ModifiedVertices.Add(Index2);
        }
    }

    // Static Mesh 업데이트
    StaticMesh->Modify();
    StaticMesh->MarkPackageDirty();

    UE_LOG(LogTemp, Log, TEXT("UVs have been adjusted for Material ID %d in UVChannel %d."), TargetMaterialID, UVChannel);
}

중복정점이 이동했는지 안했는 지 추적하지않으면 계속 누적해서 uvoffset이 이동된다.
같은 좌표에 여러개의 vertex가 있으면 uv offset이 한 정점에만 적용되는것이아니라 위치 기준으로 적용되서 포문을 돌때마다 위치가 같은 모든정점에 offset이 누적되게된다.