/ue-materials-rendering

name: ue-materials-rendering
description: "Use when the user is working with material, shader, MID, dynamic material, material instance, post-process, render target, parameter collection, decal, Nanite, Lumen, or rendering in Unreal Engine. See references/material-parameter-reference.md for parameter patterns and references/post-process-settings.md for post-process settings. For particle rendering, see ue-niagara-effects."
metadata:
  version: 1.0.0

UE Materials and Rendering

You are an expert in Unreal Engine's material and rendering systems. You provide accurate C++ patterns for dynamic materials, parameter collections, post-process, render targets, decals, and UE5 rendering features (Nanite, Lumen, Virtual Shadow Maps).

---

Step 1: Read Project Context

Read `.agents/ue-project-context.md` before giving advice. From it, extract:

• **Engine version** — UE5.0–5.4 APIs differ (e.g., `SetNaniteOverride` added in 5.x; `CopyScalarAndVectorParameters` signature changed in 5.7)
• **Target platforms** — Mobile requires forward rendering; many post-process features are desktop-only
• **Rendering settings** — Nanite/Lumen enabled status affects which material features are safe
• **Module names** — needed for correct `#include` paths and `Build.cs` dependencies

If the context file is missing, ask for engine version and target platforms before proceeding.

---

Step 2: Clarify the Rendering Need

Ask which area the user needs:

1. **Dynamic Material Instances (MID)** — runtime parameter changes on mesh components 2. **Material Parameter Collections** — global parameters shared across all materials 3. **Post-Process** — bloom, exposure, color grading, DOF, AO via volumes or components 4. **Render Targets** — scene capture, minimap, security camera, canvas drawing 5. **Decals** — deferred decals spawned at runtime, fade, sort order 6. **Rendering Pipeline / UE5 Features** — Nanite, Lumen, Virtual Shadow Maps, custom depth/stencil

Multiple areas can be combined.

---

Core Patterns

1. Dynamic Material Instances (MID)

Creation

**Pattern A — from UMaterialInterface (standalone, not tied to a component slot):**

// Header
UPROPERTY()
TObjectPtr<UMaterialInstanceDynamic> MyMID;

// Implementation — call once (BeginPlay or equivalent), cache the result
UMaterialInterface* BaseMat = LoadObject<UMaterialInterface>(
    nullptr, TEXT("/Game/Materials/M_MyBase.M_MyBase"));

MyMID = UMaterialInstanceDynamic::Create(BaseMat, this);

**Pattern B — via component slot (preferred for meshes):**

// UMeshComponent::CreateDynamicMaterialInstance creates a MID for the given
// element index and assigns it to the slot automatically.
// Signature: CreateDynamicMaterialInstance(int32 ElementIndex,
//                UMaterialInterface* SourceMaterial = nullptr,
//                FName OptionalName = NAME_None)

UMaterialInstanceDynamic* MID = MeshComponent->CreateDynamicMaterialInstance(
    0,            // element index
    nullptr,      // nullptr = use the slot's current material as parent
    TEXT("MyMID") // optional debug name
);

Source: `MaterialInstanceDynamic.h`, `PrimitiveComponent.h`. Build.cs: `"Engine"`.

Setting Parameters

MyMID->SetScalarParameterValue(TEXT("Opacity"), 0.5f);
MyMID->SetVectorParameterValue(TEXT("BaseColor"), FLinearColor(1.f, 0.2f, 0.1f, 1.f));
MyMID->SetVectorParameterValue(TEXT("Offset"), FLinearColor(0.f, 0.f, 100.f, 0.f)); // XYZ via FLinearColor
MyMID->SetTextureParameterValue(TEXT("DamageMask"), MyTexture);
MyMID->SetTextureParameterValue(TEXT("SecurityFeed"), RenderTargetAsset); // RT as texture

Full setter signatures from `MaterialInstanceDynamic.h`:

void SetScalarParameterValue(FName ParameterName, float Value);
void SetVectorParameterValue(FName ParameterName, FLinearColor Value);  // Pass FLinearColor; no implicit conversion from FVector
void SetTextureParameterValue(FName ParameterName, UTexture* Value);

High-Frequency Updates — Index-Based API

When setting dozens of parameters per frame (rare but valid), use index caching:

// In BeginPlay or initialization — call once per parameter name:
int32 OpacityIndex = -1;
MyMID->InitializeScalarParameterAndGetIndex(TEXT("Opacity"), 1.0f, OpacityIndex);

// In Tick — use index, no name lookup:
if (OpacityIndex >= 0)
{
    MyMID->SetScalarParameterByIndex(OpacityIndex, NewOpacity);
}

Index is invalidated if the parent material changes. Do not share indices across different MID instances.

MID Lifecycle and GC

MIDs are `UObject`s — they are garbage collected when unreferenced. To keep a MID alive:

// In your class header — must be UPROPERTY to prevent GC
UPROPERTY()
TObjectPtr<UMaterialInstanceDynamic> CachedMID;

Never store MIDs in raw pointers or local variables across frames.

Additional MID Operations

// Lerp between two instances' scalar/vector params
MyMID->K2_InterpolateMaterialInstanceParams(InstanceA, InstanceB, Alpha);

// Assign Nanite-compatible override material (UE5)
MyMID->SetNaniteOverride(NaniteCompatibleMaterial);

---

2. Material Parameter Collections

`UMaterialParameterCollection` is an asset holding scalar and vector parameters accessible from any material via `CollectionParameter` expression. One GPU buffer update propagates to all referencing materials. Source: `MaterialParameterCollection.h`, `MaterialParameterCollectionInstance.h`.

Setting Parameters at Runtime

// MyCollection is a UPROPERTY(EditAnywhere) pointing to the MPC asset.
UPROPERTY(EditAnywhere, Category="Rendering")
TObjectPtr<UMaterialParameterCollection> GlobalRenderingCollection;

// At runtime — get the per-world instance and set values:
void AMyActor::UpdateGlobalWeather(float RainIntensity, FLinearColor FogColor)
{
    UMaterialParameterCollectionInstance* Instance =
        GetWorld()->GetParameterCollectionInstance(GlobalRenderingCollection);

    if (Instance)
    {
        Instance