In this post we’re going to see how we can paint vertices during runtime. This post was created with Unreal Engine 4.20 so if you’re using another version you may need to update the code to match Epic’s API for the engine you’re using. It’s worth mentioning that the following code runs in packaged builds as well.
Download the source code from my GitHub repoAdding the required Dependencies
Before typing any code go into <MyProject>.Build.cs file and add the RenderCore dependency:
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PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "RenderCore" }); |
Creating the required Materials
In order for our code to work, we need to assign the following material in the static meshes we want to paint. As you may have noticed it’s the same material we’ve used in the “Creating Procedural Meshes” post:
Painting vertices at runtime
To paint all the vertices at runtime, I have created a Blueprint function library with the following public function:
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UFUNCTION(BlueprintCallable, Category = VertexPainting) static void PaintSMVertices(UStaticMeshComponent* SMComp); |
Here is the code that we need to execute in order to paint the vertices of the mesh:
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void UVertexPaintingFunctionLibrary::PaintSMVertices(UStaticMeshComponent* SMComp) { if (!SMComp) return; //Get the static mesh that we're going to paint UStaticMesh* SM = SMComp->GetStaticMesh(); if (SM) { //Get the vertex buffer from the 1st lod //FPositionVertexBuffer* PositionVertexBuffer = &SM->RenderData->LODResources[0].VertexBuffers.PositionVertexBuffer; //Make sure that we have at least 1 LOD SMComp->SetLODDataCount(1, SMComp->LODData.Num()); FStaticMeshComponentLODInfo* LODInfo = &SMComp->LODData[0]; //We're going to modify the 1st LOD only //Empty the painted vertices and assign a new color vertex buffer which will contain the new colors for each vertex LODInfo->PaintedVertices.Empty(); LODInfo->OverrideVertexColors = new FColorVertexBuffer(); //We're going to use the LODResources to get the total number of vertices that the provided mesh has FStaticMeshLODResources& LodResources = SM->RenderData->LODResources[0]; //Creating a color array TArray<FColor> RandomColorArray; //Since we know beforehand the number of elements we might as well reserve the memory now RandomColorArray.Reserve(LodResources.GetNumVertices() - 1); for (int32 i = 0; i < LodResources.GetNumVertices(); i++) { //Generate a random color for the current vertex RandomColorArray.Add(FColor::MakeRandomColor()); } //Initialize the new vertex colros with the array we created above LODInfo->OverrideVertexColors->InitFromColorArray(RandomColorArray); //Initialize resource and mark render state of object as dirty in order for the engine to re-render it BeginInitResource(LODInfo->OverrideVertexColors); SMComp->MarkRenderStateDirty(); } } |
Just for demonstration purposes, I created a Blueprint with a static mesh that has the the M_VertexColors material I created above and inside the Tick function I connected the Static Mesh component with the PaintSMVertices and here’s the end result:
love it
This is pretty amazing.
One question: I realized, that when you move, scale or rotate the pivot of the object (in the editor), the Vertex Color is overwritten (I guess by the default Color).
Is there any way to overwrite the color peramently?
Great Work, thanks, Mirko
Thanks for posting this – I followed along with most of It (not being a C++ coder). When I build and compile it – in Visual Studio – there’s no problems, and the blueprint project builds/compiles as well. However, as soon as I try to run it (in the editor) it crashes straight out of UE4. I’m using UE4.26.1, and I was wondering if you knew whether they had changed any of the code base that would have stopped this from working (and what the problem might be). I updated the build.cs file with the dependency, and built and used the vertex based material. I’d really like to get this working, as it should be very close to what I want to do (I want to have a Line of sight -dependent material (that I will use the vertex color as a mask for).