Dynamically create mesh from points in space

[shue_it]

Hello there

I would like to create a Mesh from several points (world coordinates if possible), by clicking on the ground to draw a shape for instance.

I did some researches beforehand, and roughly found two ways I can explore :

• Using Procedural Mesh (Procedural Mesh Component), where I need to give vertices, triangles and so on. A similar post would be this : Dynamical mesh in blueprint from array of vertex-coordinates of the polygon perimeter in the space? . But it may not be the way to do it anymore ( Reddit - Mesh generation in Unreal Engine ) ?
• Using the plugin GeometryScript, but it’s experimental and its documentation is still scarce. It seems to be really powerful when seeing this like this or more impressive in this article, but I’m struggling to use it. I somewhat managed to add vertices to a mesh, and of course nothing is visible in game so things are still missing, but I don’t know what (creating normals ? UVs ?)
  Here is the code I wrote

	const TSharedPtr<TArray<FVector>> sharedVertices = MakeShared<TArray<FVector>>(vertices); 
	FGeometryScriptVectorList verticesList = FGeometryScriptVectorList { sharedVertices }; 

	const TSharedPtr<TArray<int>> indexes = MakeShared<TArray<int>>();
	FGeometryScriptIndexList indexesList = FGeometryScriptIndexList { EGeometryScriptIndexType::Vertex ,indexes };
	
	UDynamicMesh* myDynMesh = this->DynamicMeshComponent->GetDynamicMesh()->Reset();
	UGeometryScriptLibrary_MeshBasicEditFunctions::AddVerticesToMesh(myDynMesh, std::move(verticesList), indexesList);

Any advice ?
Thank you ^^

[shue_it]

I dig on the source code of this Demo GitHub - gradientspace/UE5RuntimeToolsFrameworkDemo: Sample project/code that uses the UE5 InteractiveToolsFramework to provide a small modeling app at Runtime and managed to cook something.

Starting with a TArray<FVector> of your vertices, append them to a FPolygon2d. The coordinates of the vertices are local to the Polygon.

FPolygon2d OuterPolygon;
for (FVector& Vertex : Vertices)
{
	OuterPolygon.AppendVertex(TVector2(Vertex));
}

Then, ensure that your vertices order is counter-clockwise (otherwise your mesh will be reversed)

if(OuterPolygon.IsClockwise())
{
	OuterPolygon.Reverse();
}

NB : If you’re sure about the correct order of your vertices, you don’t need those 2 steps. But you will still need your vertices as FVector2D (and not FVector).

Then, use AppendSimpleExtrudePolygon function and tada. No need to compute triangles.

// Just in case, resetting all data for the Dynamic Mesh
UDynamicMesh* MyDynMesh = this->DynamicMeshComponent->GetDynamicMesh()->Reset();

UGeometryScriptLibrary_MeshPrimitiveFunctions::AppendSimpleExtrudePolygon(MyDynMesh,
	FGeometryScriptPrimitiveOptions(),
	FTransform(),
	OuterPolygon.GetVertices(), //Vertices2D,
	100, // Height
	5);  // HeightSteps, dunno what it does

Also, you can add this line, otherwise the normals are weird (but I can’t explain why)

UGeometryScriptLibrary_MeshNormalsFunctions::ComputeSplitNormals(MyDynMesh, FGeometryScriptSplitNormalsOptions(), FGeometryScriptCalculateNormalsOptions());

Note that it uses some experimental functions and AppendSimpleExtrudePolygon seems to not be available in any namespace ? Hence, I needed to do an import with relative path like that (UE 5.0.3)
#include "../Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshPrimitiveFunctions.h"
(same thing for ComputeSplitNormals)

This may not be a clean way to do it, but for now it’s the only way I managed to find with my (restricted) knowledge.