1、通过MeshDescription在运行时构建StaticMesh并设置碰撞、修改材质

1、MyActor.h

//MyActor.h
#pragma once
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "MyActor.generated.h"
UCLASS()
class CONTROLLER_API AMyActor : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	AMyActor();
	UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Polygon")
	TObjectPtr PolygonComponent;
	FPolygonGroupID GroupId;
	UPROPERTY(EditAnywhere, Category = "Polygon")
	TArray Coodinates;
	TObjectPtr Polygon;
	UPROPERTY(EditAnywhere, Category = "Polygon")
	UMaterialInterface* Material;
protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;
	virtual void OnConstruction(const FTransform& Transform) override;
public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;
	TObjectPtr BuildPolygon(TArray InPositions);
};

2、MyActor.cpp

//MyActor.cpp
#include "MyActor.h"
#include "StaticMeshAttributes.h"
#include "CompGeom/PolygonTriangulation.h"
#include 
#include 
// Sets default values
AMyActor::AMyActor()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;
	PolygonComponent = CreateDefaultSubobject(TEXT("PolygonComponent"), false);
	SetRootComponent(PolygonComponent);
}
// Called when the game starts or when spawned
void AMyActor::BeginPlay()
{
	Super::BeginPlay();
	if(Coodinates.Num())
	{
		Material = LoadObject(this, TEXT("/Engine/BasicShapes/BasicShapeMaterial.BasicShapeMaterial"));
		PolygonComponent->SetStaticMesh(BuildPolygon(Coodinates));
		PolygonComponent->SetMaterial(0,Material);
		//PolygonComponent->SetForcedLodModel(1);
	}
}
void AMyActor::OnConstruction(const FTransform& Transform)
{
	if (!IsTemplate()) {
		if (Coodinates.Num())
		{
			//加载虚幻引擎自带的材质
			Material = LoadObject(this, TEXT("/Engine/BasicShapes/BasicShapeMaterial.BasicShapeMaterial"));
			//将生成的StaticMesh挂载到StaticMeshComponent上
			BuildPolygon(Coodinates);
			PolygonComponent->SetStaticMesh(Polygon);
			//在StaticMeshComponent上设置材质，坑1：StaticMesh也有一个SetMaterial方法，但是它是仅在编辑器状态下可用的，调用了这个方法打包时会报错，打包就失败了，而StaticMeshComponent的SetMaterial方法没有这个问题，且材质能够成功应用到StaticMesh上
			PolygonComponent->SetMaterial(0, Material);
		}
	}
}
// Called every frame
void AMyActor::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);
}
FBox2D computeMinRectangle(TArray InPositions)
{
	FBox2D result;
	uint8 num = InPositions.Num();
	if (num  currentPoint.X ? maxX : currentPoint.X;
		maxY = maxY > currentPoint.Y ? maxY : currentPoint.Y;
		minX = minX GetStaticMaterials().Add(FStaticMaterial());
	FMeshDescription meshDesc;
	FStaticMeshAttributes attributes(meshDesc);
	//注册默认的静态模型属性
	attributes.Register();
	//FMeshDescriptionBuilder用于设置顶点、法线、UV坐标等信息
	FMeshDescriptionBuilder meshDescBuilder;
	meshDescBuilder.SetMeshDescription(&meshDesc);
	//允许使用多边形组
	meshDescBuilder.EnablePolyGroups();
	//设置UV坐标的级数为1
	meshDescBuilder.SetNumUVLayers(1);
	TArray vertexIDs;
	const int count = InPositions.Num();
	vertexIDs.SetNum(count);
	TArray Positions2D;
	for (int32 i = 0; i BuildFromMeshDescriptions(meshDescPtrs, mdParams);
	
	//坑3：如果要给StaticMeshComponent绑定鼠标的click、hover等时间的话，需要调用下面这段代码以启用复杂碰撞，因为click等事件也是基于射线检测进行判断的，但是它检测的是复杂碰撞(TraceComplex参数值为true)，因此如果不调用下面这段代码，click等事件是不会生效的。注意：这里不要创建BodySetup,在前面的BuildFromMeshDescriptions方法的函数实现里面已经为StaticMesh创建了一个BodySetup，并为其赋予了一些值。
		if (UBodySetup* bodySetup = Polygon->GetBodySetup())
	{
		bodySetup->DefaultInstance.SetCollisionProfileName(UCollisionProfile::BlockAll_ProfileName);
		bodySetup->CollisionTraceFlag = CTF_UseSimpleAsComplex;
		bodySetup->bGenerateMirroredCollision = false;
	}
	return Polygon;
}

3、总结

1）运行时修改StaticMesh的材质要调用StaticMeshComponent的SetMaterial方法而不是StaticMesh的SetMaterial方法，因为StaticMesh的SetMaterial方法仅在编辑器状态下可用，会导致你打包失败；

2）想要在运行时修改StaticMesh的材质，首先要确保StaticMesh有材质插槽，为StaticMesh增加材质插槽的方法如上，一定不能使用StaticMesh的AddMaterial方法，运行时状态下无效；

3）想要给StaticMesh绑定click、hover等事件，需要为其启用复杂碰撞，代码如上，但是不使用那段代码也有碰撞，只是click、hover等事件不生效。