391 lines
16 KiB
Markdown
391 lines
16 KiB
Markdown
---
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title: 基于插件的SkeletalMesh多Pass绘制方案
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date: 2022-11-04 10:25:07
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excerpt:
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tags:
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rating: ⭐
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---
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>本文仅供抛转引玉，为大家提供一个可行思路。因为本人目前仅仅是个Ue4业余爱好者，手头没有含有Lod的骨骼模型做测试，所以请勿在未测试的情况下直接把本插件用于生产。
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## 前言
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在阅读了 @白昼行姜暗夜摸王 的系列文章，我感觉通过改引擎的方式来实现模型外描边着实不太方便。在仔细阅读代码后，发现文章中修改代码的相关函数，不是虚函数就是包含在虚函数中。于是乎我就感觉可以通过插件的方式来实现多pass的绘制方案，便开始尝试。
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另外感谢@大钊 @YivanLee 在我尝试过程中给予的帮助。
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## 思路说明
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>在重写函数的过程中，因为引擎部分类是定义在cpp中，以及部分函数因为没有ENGINE_API或是Private导致无法无法使用。有一个lod更新的逻辑我实在没办法绕过，所以就删除了。所以这个插件对于有lod的模型可能会有问题，解决思路我会说。
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### 创建自定义SkeletalMeshComponent类
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1. 继承USkeletalMeshComponent,重写GetUsedMaterials与CreateSceneProxy函数。
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2. 添加用于多pass渲染的UMaterialInterface指针。（NeedSecondPass变量其实可以不用，因为既然你要使用这个类，那肯定要启用这个功能）
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```c++
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#pragma once
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#include "CoreMinimal.h"
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#include "Engine/Classes/Components/SkeletalMeshComponent.h"
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#include "StrokeSkeletalMeshComponent.generated.h"
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UCLASS(ClassGroup=(Rendering, Common), hidecategories=Object, editinlinenew, meta=(BlueprintSpawnableComponent))
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class UStrokeSkeletalMeshComponent : public USkeletalMeshComponent
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{
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GENERATED_UCLASS_BODY()
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//~ Begin UPrimitiveComponent Interface
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virtual void GetUsedMaterials(TArray<UMaterialInterface*>& OutMaterials, bool bGetDebugMaterials = false) const override;
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virtual FPrimitiveSceneProxy* CreateSceneProxy() override;
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//~ End UPrimitiveComponent Interface
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//virtual UMaterialInterface* GetMaterial(int32 MaterialIndex) const override;
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public:
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UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "MultiplePass")
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UMaterialInterface* SecondPassMaterial = nullptr;
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UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "MultiplePass")
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bool NeedSecondPass=false;
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};
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```
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3. 实现GetUsedMaterials与CreateSceneProxy函数，并包含相应头文件。
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### 头文件
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```c++
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#include "StrokeSkeletalMeshComponent.h"
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#include "StrokeSkeletalMeshSceneProxy.h"
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#include "Engine/Public/Rendering/SkeletalMeshRenderData.h"
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#include "Engine/Public/SkeletalRenderPublic.h"
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```
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### GetUsedMaterials
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自定义的SkeletalMeshComponent只运行OutMaterials.Add(SecondPassMaterial);会导致引擎找不到Material的ShaderMap。在尝试之处，我追踪了Skeletal的MeshDraw绘制流程，发现竟然是VertexFactory指针为空造成的。所以我判断应该是自定义的Component没有把Material进行注册造成的问题。
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之后我尝试了手动将MaterialInterface的指针添加到SkeletalMesh的Lod数组中的material。虽然解决了问题，但是遇到重复修改会导致组件栏里多出一堆材质asset显示，虽然之后通过判断slotname进行数组管理解决了问题，但是结果还是不完美。
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不过之后在继续查看了源代码后，我发现只要调用UpdateUVChannelData就可以解决问题。
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```c++
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void UStrokeSkeletalMeshComponent::GetUsedMaterials(TArray<UMaterialInterface*>& OutMaterials, bool bGetDebugMaterials /*= false*/) const
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{
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if (SkeletalMesh)
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{
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// The max number of materials used is the max of the materials on the skeletal mesh and the materials on the mesh component
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const int32 NumMaterials = FMath::Max(SkeletalMesh->Materials.Num(), OverrideMaterials.Num());
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for (int32 MatIdx = 0; MatIdx < NumMaterials; ++MatIdx)
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{
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// GetMaterial will determine the correct material to use for this index.
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UMaterialInterface* MaterialInterface = GetMaterial(MatIdx);
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OutMaterials.Add(MaterialInterface);
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}
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//这里是我添加的代码
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if (NeedSecondPass)
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{
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OutMaterials.Add(SecondPassMaterial);
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SkeletalMesh->UpdateUVChannelData(false);
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}
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}
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if (bGetDebugMaterials)
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{
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#if WITH_EDITOR
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//这段代码无法绕过，而且因为不太重要，就直接注释掉了
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//if (UPhysicsAsset* PhysicsAssetForDebug = GetPhysicsAsset())
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//{
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// PhysicsAssetForDebug->GetUsedMaterials(OutMaterials);
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//}
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#endif
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}
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}
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```
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### CreateSceneProxy
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CreateSceneProxy比较简单，只需要创建自己的自定义Proxy就可以了
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```c++
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FPrimitiveSceneProxy* UStrokeSkeletalMeshComponent::CreateSceneProxy()
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{
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ERHIFeatureLevel::Type SceneFeatureLevel = GetWorld()->FeatureLevel;
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//定义自定义Proxy类指针
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FStrokeSkeletalMeshSceneProxy* Result = nullptr;
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//FSkeletalMeshSceneProxy* Result = nullptr;
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FSkeletalMeshRenderData* SkelMeshRenderData = GetSkeletalMeshRenderData();
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// Only create a scene proxy for rendering if properly initialized
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if (SkelMeshRenderData &&
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SkelMeshRenderData->LODRenderData.IsValidIndex(PredictedLODLevel) &&
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!bHideSkin &&
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MeshObject)
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{
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// Only create a scene proxy if the bone count being used is supported, or if we don't have a skeleton (this is the case with destructibles)
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int32 MaxBonesPerChunk = SkelMeshRenderData->GetMaxBonesPerSection();
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int32 MaxSupportedNumBones = MeshObject->IsCPUSkinned() ? MAX_int32 : GetFeatureLevelMaxNumberOfBones(SceneFeatureLevel);
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if (MaxBonesPerChunk <= MaxSupportedNumBones)
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{
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//使用new创建指针对象
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Result = ::new FStrokeSkeletalMeshSceneProxy(this, SkelMeshRenderData);
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}
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}
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#if !(UE_BUILD_SHIPPING || UE_BUILD_TEST)
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SendRenderDebugPhysics(Result);
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#endif
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return Result;
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}
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```
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### 创建自定义SkeletalMeshSceneProxy类
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1. 继承FSkeletalMeshSceneProxy,重写GetDynamicMeshElements函数。
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2. 定义USkinnedMeshComponent指针，用于获取自定义SkeletalMeshComponent的变量。（之后使用需要使用强制转换）
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```c++
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#pragma once
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#include "Engine/Public/SkeletalMeshTypes.h"
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class FStrokeSkeletalMeshSceneProxy : public FSkeletalMeshSceneProxy
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{
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public:
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//在UStrokeSkeletalMeshComponent中调用这个构造函数初始化
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FStrokeSkeletalMeshSceneProxy(const USkinnedMeshComponent* Component, FSkeletalMeshRenderData* InSkelMeshRenderData);
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virtual void GetDynamicMeshElements(const TArray<const FSceneView*>& Views, const FSceneViewFamily& ViewFamily, uint32 VisibilityMap, FMeshElementCollector& Collector) const override;
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private:
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UPROPERTY()
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const USkinnedMeshComponent* ComponentPtr;
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};
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```
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```c++
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FStrokeSkeletalMeshSceneProxy::FStrokeSkeletalMeshSceneProxy(const USkinnedMeshComponent* Component, FSkeletalMeshRenderData* InSkelMeshRenderData):
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FSkeletalMeshSceneProxy(Component,InSkelMeshRenderData),ComponentPtr(Component)
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{}
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```
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3. 实现GetDynamicMeshElements函数，并包含头文件。
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### 头文件
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```c++
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#include "StrokeSkeletalMeshSceneProxy.h"
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#include "Engine/Public/SkeletalMeshTypes.h"
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#include "Engine/Public/TessellationRendering.h"
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#include "Engine/Public/SkeletalRenderPublic.h"
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```
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### GetDynamicMeshElements
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```c++
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void FStrokeSkeletalMeshSceneProxy::GetDynamicMeshElements(const TArray<const FSceneView*>& Views, const FSceneViewFamily& ViewFamily, uint32 VisibilityMap, FMeshElementCollector& Collector) const
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{
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QUICK_SCOPE_CYCLE_COUNTER(STAT_FStrokeSkeletalMeshSceneProxy_GetMeshElements);
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if (!MeshObject)
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{
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return;
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}
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MeshObject->PreGDMECallback(ViewFamily.Scene->GetGPUSkinCache(), ViewFamily.FrameNumber);
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//这句代码无法绕过，所以只能注释掉了
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/*
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
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{
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if (VisibilityMap & (1 << ViewIndex))
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{
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const FSceneView* View = Views[ViewIndex];
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MeshObject->UpdateMinDesiredLODLevel(View, GetBounds(), ViewFamily.FrameNumber);
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}
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}
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*/
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const FEngineShowFlags& EngineShowFlags = ViewFamily.EngineShowFlags;
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const int32 LODIndex = MeshObject->GetLOD();
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check(LODIndex < SkeletalMeshRenderData->LODRenderData.Num());
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const FSkeletalMeshLODRenderData& LODData = SkeletalMeshRenderData->LODRenderData[LODIndex];
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if (LODSections.Num() > 0)
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{
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const FLODSectionElements& LODSection = LODSections[LODIndex];
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check(LODSection.SectionElements.Num() == LODData.RenderSections.Num());
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for (FSkeletalMeshSectionIter Iter(LODIndex, *MeshObject, LODData, LODSection); Iter; ++Iter)
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{
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const FSkelMeshRenderSection& Section = Iter.GetSection();
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const int32 SectionIndex = Iter.GetSectionElementIndex();
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const FSectionElementInfo& SectionElementInfo = Iter.GetSectionElementInfo();
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bool bSectionSelected = false;
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#if WITH_EDITORONLY_DATA
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// TODO: This is not threadsafe! A render command should be used to propagate SelectedEditorSection to the scene proxy.
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if (MeshObject->SelectedEditorMaterial != INDEX_NONE)
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{
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bSectionSelected = (MeshObject->SelectedEditorMaterial == SectionElementInfo.UseMaterialIndex);
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}
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else
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{
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bSectionSelected = (MeshObject->SelectedEditorSection == SectionIndex);
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}
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#endif
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//下面函数的代码
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// If hidden skip the draw
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check(MeshObject->LODInfo.IsValidIndex(LODIndex));
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bool bHide= MeshObject->LODInfo[LODIndex].HiddenMaterials.IsValidIndex(SectionElementInfo.UseMaterialIndex) && MeshObject->LODInfo[LODIndex].HiddenMaterials[SectionElementInfo.UseMaterialIndex];
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if (bHide || Section.bDisabled)
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{
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continue;
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}
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//这个函数因为没有导出，但是比较简单所以上面就直接把代码复制出来了
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/* error LNK2019
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if (MeshObject->IsMaterialHidden(LODIndex, SectionElementInfo.UseMaterialIndex) || Section.bDisabled)
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{
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continue;
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}
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*/
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const UStrokeSkeletalMeshComponent* StrokeSkeletalMeshComponent = dynamic_cast<const UStrokeSkeletalMeshComponent *>(ComponentPtr);
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if (SectionElementInfo.Material== StrokeSkeletalMeshComponent->SecondPassMaterial)
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{
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continue;
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}
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GetDynamicElementsSection(Views, ViewFamily, VisibilityMap, LODData, LODIndex, SectionIndex, bSectionSelected, SectionElementInfo, true, Collector);
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//进行第二个pass绘制
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//关键点在于修改FSectionElementInfo中的Material，并且再次调用绘制函数GetDynamicElementsSection
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if (StrokeSkeletalMeshComponent->NeedSecondPass) {
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FSectionElementInfo Info = FSectionElementInfo(SectionElementInfo);
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if (StrokeSkeletalMeshComponent->SecondPassMaterial == nullptr) {
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continue;
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}
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Info.Material = StrokeSkeletalMeshComponent->SecondPassMaterial;
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GetDynamicElementsSection(Views, ViewFamily, VisibilityMap, LODData, LODIndex, SectionIndex, bSectionSelected, Info, true, Collector);
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}
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}
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}
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#if !(UE_BUILD_SHIPPING || UE_BUILD_TEST)
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
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{
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if (VisibilityMap & (1 << ViewIndex))
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{
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if (PhysicsAssetForDebug)
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{
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DebugDrawPhysicsAsset(ViewIndex, Collector, ViewFamily.EngineShowFlags);
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}
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if (EngineShowFlags.MassProperties && DebugMassData.Num() > 0)
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{
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FPrimitiveDrawInterface* PDI = Collector.GetPDI(ViewIndex);
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if (MeshObject->GetComponentSpaceTransforms())
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{
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const TArray<FTransform>& ComponentSpaceTransforms = *MeshObject->GetComponentSpaceTransforms();
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for (const FDebugMassData& DebugMass : DebugMassData)
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{
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if (ComponentSpaceTransforms.IsValidIndex(DebugMass.BoneIndex))
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{
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const FTransform BoneToWorld = ComponentSpaceTransforms[DebugMass.BoneIndex] * FTransform(GetLocalToWorld());
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DebugMass.DrawDebugMass(PDI, BoneToWorld);
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}
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}
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}
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}
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if (ViewFamily.EngineShowFlags.SkeletalMeshes)
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{
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RenderBounds(Collector.GetPDI(ViewIndex), ViewFamily.EngineShowFlags, GetBounds(), IsSelected());
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}
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if (ViewFamily.EngineShowFlags.Bones)
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{
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DebugDrawSkeleton(ViewIndex, Collector, ViewFamily.EngineShowFlags);
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}
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}
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}
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#endif
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}
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```
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>UpdateMinDesiredLODLevel函数处的代码被我注释掉了，大致的解决方法为：调用父类的GetDynamicMeshElements函数，再运行一次GetDynamicElementsSection绘制自己的pass。
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下面的代码我没测试过，仅为说明意思，很多地方是父类运行过的逻辑，可以删除。
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```c++
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QUICK_SCOPE_CYCLE_COUNTER(STAT_FStrokeSkeletalMeshSceneProxy_GetMeshElements);
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//运行父类函数
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FStrokeSkeletalMeshSceneProxy::GetDynamicMeshElements(Views,ViewFamily,VisibilityMap,Collector);
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const FEngineShowFlags& EngineShowFlags = ViewFamily.EngineShowFlags;
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const int32 LODIndex = MeshObject->GetLOD();
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check(LODIndex < SkeletalMeshRenderData->LODRenderData.Num());
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const FSkeletalMeshLODRenderData& LODData = SkeletalMeshRenderData->LODRenderData[LODIndex];
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if (LODSections.Num() > 0)
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{
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const FLODSectionElements& LODSection = LODSections[LODIndex];
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check(LODSection.SectionElements.Num() == LODData.RenderSections.Num());
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for (FSkeletalMeshSectionIter Iter(LODIndex, *MeshObject, LODData, LODSection); Iter; ++Iter)
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{
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const FSkelMeshRenderSection& Section = Iter.GetSection();
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const int32 SectionIndex = Iter.GetSectionElementIndex();
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const FSectionElementInfo& SectionElementInfo = Iter.GetSectionElementInfo();
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bool bSectionSelected = false;
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#if WITH_EDITORONLY_DATA
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// TODO: This is not threadsafe! A render command should be used to propagate SelectedEditorSection to the scene proxy.
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if (MeshObject->SelectedEditorMaterial != INDEX_NONE)
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{
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bSectionSelected = (MeshObject->SelectedEditorMaterial == SectionElementInfo.UseMaterialIndex);
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}
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else
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{
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bSectionSelected = (MeshObject->SelectedEditorSection == SectionIndex);
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}
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#endif
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//下面函数的代码
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// If hidden skip the draw
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check(MeshObject->LODInfo.IsValidIndex(LODIndex));
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bool bHide= MeshObject->LODInfo[LODIndex].HiddenMaterials.IsValidIndex(SectionElementInfo.UseMaterialIndex) && MeshObject->LODInfo[LODIndex].HiddenMaterials[SectionElementInfo.UseMaterialIndex];
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if (bHide || Section.bDisabled)
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{
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continue;
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}
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const UStrokeSkeletalMeshComponent* StrokeSkeletalMeshComponent = dynamic_cast<const UStrokeSkeletalMeshComponent *>(ComponentPtr);
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if (SectionElementInfo.Material== StrokeSkeletalMeshComponent->SecondPassMaterial)
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{
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continue;
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}
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//进行第二个pass绘制
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//关键点在于修改FSectionElementInfo中的Material，并且再次调用绘制函数GetDynamicElementsSection
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if (StrokeSkeletalMeshComponent->NeedSecondPass) {
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FSectionElementInfo Info = FSectionElementInfo(SectionElementInfo);
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if (StrokeSkeletalMeshComponent->SecondPassMaterial == nullptr) {
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continue;
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}
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Info.Material = StrokeSkeletalMeshComponent->SecondPassMaterial;
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GetDynamicElementsSection(Views, ViewFamily, VisibilityMap, LODData, LODIndex, SectionIndex, bSectionSelected, Info, true, Collector);
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}
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}
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}
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```
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4. 解决FSkeletalMeshSectionIter未定义的报错问题。(原因在开头说了)
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在Engine\Source\Runtime\Engine\Private\SkeletalMesh.cpp中找到FSkeletalMeshSectionIter类，并将所有代码复制到你定义的SkeletalMeshSceneProxy所在的cpp文件中。
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完成以上步骤你就得到一个2个pass的SkeletalMeshComponent。
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## 关于绘制轮廓的问题
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@白昼行姜暗夜摸王 的文章采用了使用了绘制背面的方法来得到轮廓，但是很可惜，因为以下原因，我无法在不修改源码的情况下实现这个方法：
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1. SkeletalMeshSceneProxy的MeshBatch设置逻辑在绘制函数中。
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2. 因为绘制函数有很多核心函数因为没倒出或是private，所以无法重写。
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3. 判断剔除的IsLocalToWorldDeterminantNegative()函数不是虚函数。
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4. bIsLocalToWorldDeterminantNegative是父类的private变量，无法修改。
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当然可以使用一些c++黑科技来突破（3、4），不过我暂时没有那种技术。
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## 曲线救国方法
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绘制背面本质上还是一种深度偏移，所以我们可以采用深度偏移的方法来解决。
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材质我没有仔细调，所以在离模型较远的地方会显得有点“脏”，只需要在Mask与深度偏移添加模型距离的判断来，进行参数调整就完美。
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## 插件地址及使用方法
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### 插件地址
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https://github.com/blueroseslol/BRPlugins
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### 使用方法
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1. 创建一个Actor蓝图。
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2. 创建你定义的SkeletalMeshComponent。
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3. 赋予轮廓材质，并勾选NeedSecondPass。
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## 延伸思考
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我觉得可以通过在自定义的Component类中定义一个TArray<MaterialInterface*>，用于存储各个Pass的材质，之后再自己定义的SceneProxy中进行for循环绘制，不就实现类似unity的多pass材质系统了。
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至少StaticMesh因为MeshBatch的设置过程，并没有在绘制函数中，所以我们可以任意修改MeshBatch设置，而可以完美实现上述猜想。下一篇文章我将介绍StaticMesh的实现方法。 |