(原) Unreal创建自定义MeshCompoent

@author:白袍小道

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前言：

绘制相关类

MeshCompoent	模型组件
FVertexBuffer	顶点缓冲区封装
FIndexBuffer	顶点索引缓冲区封装
FRHIResourceCreateInfo	资源创建描述，分装了底层（DX,OPENGL)的资源（如缓冲区）的描述
FMemory	C++内存操作封装
RHIUnlockIndexBuffer	？？？？？？？？
FPrimitiveSceneProxy	为渲染线程映射 UPrimitiveComponent 状态。划分为子类以支持不同类型的基元（骨架、刚体、BSP 等）实现某些非常重要的函数.
FSceneView	单个视图到一个 FScene 的引擎代表。通过对 FSceneRenderer::Render 的不同调用的不同视图来渲染（多编辑器视口）通过对 FSceneRenderer::Render 的同一调用中的多个视图来渲染（分屏游戏）。为每个帧构建新视图
FSceneViewFamily	一组视图进入一个场景，该场景有不同的视图转换和所有者角色，所以有个管理（维护）
FMeshElementCollector
FDynamicMeshBuilder

绘制规则

Constructor ： 从给定的顶点工厂(vertex factory)和材质着色器列表(material shader map)找出适当的着色器，并存储他们的引用。

其中材质着色器可以看GlobalShader的管理部分【值得参考类比和学习】。
CreateBoundShaderState ： 为绘制规则(Drawing Policy)创建绑定到RHI的着色器状态。
Matches/Compare ： 提供了排序该drawing policy和渲染列表（draw lists）中其他drawing policy的函数，Matches 必须比较 DrawShared 依赖的所有因素。
DrawShared ： 设置在从 Matches 返回 True 的绘制规则之间一致的 RHI 状态。例如，大多数绘制规则会为材质和顶点工厂排序，因此着色器参数只依赖可以设置的材质，并且可以绑定特定于该顶点工厂的顶点缓冲区。应尽可能在此处设置状态，而非在 SetMeshRenderState 设置，因为 DrawShared 在静态渲染路径中调用较少。
SetMeshRenderState ： 设置特定于此网格体的 RHI 状态，或 DrawShared 中未设置的状态。这比 DrawShared 调用的次数多得多，因此此处性能非常重要。
DrawMesh ： 实际发出 RHI 绘制调用

参考源码及其说明

DZCPP_CustomMeshComponent_01.h

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "CoreMinimal.h"
#include "Components/MeshComponent.h"
#include <VertexFactory.h>
#include "ContentExamples.h"
#include "DynamicMeshBuilder.h"
#include "DZCPP_CustomMeshComponent_01.generated.h"

/**
*
*/
UCLASS(ClassGroup=Experimental,meta = (BlueprintSpawnableComponent))
class CONTENTEXAMPLES_API UDZCPP_CustomMeshComponent_01 : public UMeshComponent
{
GENERATED_BODY()
public:
virtual FPrimitiveSceneProxy * CreateSceneProxy() override;
TArray<int32> Indices;
TArray<FVector> Vertices;

UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Materials)
UMaterial * TheMaterial;

UDZCPP_CustomMeshComponent_01();
};

DZCPP_CustomMeshComponent_01.cpp

// Fill out your copyright notice in the Description page of Project Settings.
#include "DZCPP_CustomMeshComponent_01.h"
class FMyVertexBuffer : public FVertexBuffer
{
public:
TArray<FVector> Vertices;
virtual void InitRHI() override
{
FRHIResourceCreateInfo CreateInfo;
VertexBufferRHI = RHICreateVertexBuffer(Vertices.Num()
* sizeof(FVector), BUF_Static, CreateInfo);
void* VertexBufferData =
RHILockVertexBuffer(VertexBufferRHI, 0, Vertices.Num()
* sizeof(FVector), RLM_WriteOnly);
FMemory::Memcpy(VertexBufferData, Vertices.GetData(),
Vertices.Num() * sizeof(FVector));
RHIUnlockVertexBuffer(VertexBufferRHI);
}
};
class FMyIndexBuffer : public FIndexBuffer
{
public:
TArray<int32> Indices;
virtual void InitRHI() override
{
FRHIResourceCreateInfo CreateInfo;
IndexBufferRHI = RHICreateIndexBuffer(sizeof(int32),
Indices.Num() * sizeof(int32), BUF_Static, CreateInfo);
void* Buffer = RHILockIndexBuffer(IndexBufferRHI, 0,
Indices.Num() * sizeof(int32), RLM_WriteOnly);
FMemory::Memcpy(Buffer, Indices.GetData(),
Indices.Num() * sizeof(int32));
RHIUnlockIndexBuffer(IndexBufferRHI);
}
};

class FMySceneProxy : public FPrimitiveSceneProxy
{
private:
TArray<FDynamicMeshVertex> Vertices;
TArray<int32> Indices;
FMyVertexBuffer VertexBuffer;
FMyIndexBuffer IndexBuffer;
public:
UPROPERTY()
UMaterial* TheMaterial;
FMySceneProxy(UDZCPP_CustomMeshComponent_01* Component) :FPrimitiveSceneProxy(Component), Indices(Component->Indices), TheMaterial(Component->TheMaterial)
{
// VertexBuffer = FMyVertexBuffer();
// IndexBuffer = FMyIndexBuffer();
// for (FVector Vertex : Component->Vertices)
// {
// Vertices.Add(FDynamicMeshVertex(Component
// ->GetComponentLocation() + Vertex));
// }
}
//FPrimitiveViewRelevance GetViewRelevance(const FSceneView* View)
//{
// FPrimitiveViewRelevance Result;
// Result.bDynamicRelevance = true;
// Result.bDrawRelevance = true;
// Result.bNormalTranslucencyRelevance = true;
// return Result;
//}

//void GetDynamicMeshElements(const TArray<const
// FSceneView*>& Views, const FSceneViewFamily& ViewFamily,
// uint32 VisibilityMap, FMeshElementCollector& Collector)
//{
// for (int32 ViewIndex = 0; ViewIndex < Views.Num();
// ViewIndex++)
// {
// FDynamicMeshBuilder MeshBuilder;
// if (Vertices.Num() == 0)
// {
// return;
// }
// MeshBuilder.AddVertices(Vertices);
// MeshBuilder.AddTriangles(Indices);
// }
//}

//void FMySceneProxy::OnActorPositionChanged()
//{
// VertexBuffer.ReleaseResource();
// IndexBuffer.ReleaseResource();
//}

//uint32 FMySceneProxy::GetMemoryFootprint(void)
//{
// return sizeof(*this);
//}
virtual ~FMySceneProxy() {};
};

FPrimitiveSceneProxy* UDZCPP_CustomMeshComponent_01::CreateSceneProxy()
{
FPrimitiveSceneProxy* proxy = nullptr;
//fmysceneproxy * childproxy = new fmysceneproxy(this);
//proxy = childproxy;
return proxy;
}

UDZCPP_CustomMeshComponent_01::UDZCPP_CustomMeshComponent_01()
{
/*static ConstructorHelpers::FObjectFinder<UMaterial>Material(TEXT("Material'/Engine/BasicShapes/BasicShapeMaterial'"));
if (Material.Object != NULL)
{
TheMaterial = (UMaterial*)Material.Object;
}
Vertices.Add(FVector(10, 0, 0));
Vertices.Add(FVector(0, 10, 0));
Vertices.Add(FVector(0, 0, 10));
Indices.Add(0);
Indices.Add(1);
Indices.Add(2);*/
}