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2020-08-11_13:53:42

UMaterialInstanceConstant

A new Material Instance is created with the following code, taken from the 2016 version of FAssetTypeActions_MaterialInterface::ExecuteNewMic. https://forums.unrealengine.com/development-discussion/c-gameplay-programming/98655-create-a-material-instance (2016)

UMaterialInterface* ParentMaterial = ...;

// Create an appropriate and unique name.
FString Name;
FString PackageName;
CreateUniqueAssetName(
    ParentMaterial->GetOutermost()->GetName(),
    DefaultSuffix, PackageName, Name);

UMaterialInstanceConstantFactoryNew* Factory =
    NewObject<UMaterialInstanceConstantFactoryNew>();
Factory->InitialParent = ParentMaterial;

FContentBrowserModule& ContentBrowserModule =
    FModuleManager::LoadModuleChecked<FContentBrowserModule>(
        "ContentBrowser");
ContentBrowserModule.Get().CreateNewAsset(
    Name, FPackageName::GetLongPackagePath(PackageName),
    UMaterialInstanceConstant::StaticClass(), Factory);

The list of parameters provided by the parent material is found by calling GetStaticParameterValues on the Material Instance.

The FBX importer does stuff with Materials. At least according to https://github.com/gildor2/UEViewer/issues/118 (2019). Check Engine/Source/Editor/UnrealEd/Private/Fbx/FbxMaterialImport.cpp. UnFbx::FFbxImporter::CreateUnrealMaterial.

Example code from the gildor2 issue:

// Let's assume 'Template' is UMaterial which will be instantiated.

UMaterial* Template = ...;
UMaterialInstanceConstantFactoryNew* MaterialFactory =
    NewObject<UMaterialInstanceConstantFactoryNew>();
MaterialFactory->InitialParent = Template;

FAssetToolsModule& AssetToolsModule =
    FModuleManager::Get().LoadModuleChecked<FAssetToolsModule>(
        "AssetTools");
UObject* Asset = AssetToolsModule.Get().CreateAsset(
    InstanceName, FPackageName::GetLongPackagePath(PackagePath),
    UMaterialInstanceConstant::StaticClass(), MaterialFactory);

// Now you'll have 'Asset' which could be casted to UMaterialInstanceConstant.

UMaterialInstanceConstant* mat = Cast<UMaterialInstanceConstant>(Asset);

// Then use UMaterialInstanceConstant's methods:
// * SetTextureParameterValueEditorOnly
// * SetVectorParameterValueEditorOnly
// * SetScalarParameterValueEditorOnly

// Then, when finished, call this on material instance:
mat->SetFlags(RF_Standalone);
mat->MarkPackageDirty();
mat->PostEditChange();

The two example implementations are very similar. One difference is that one uses the ContentBrowserModule while the other uses the AssetToolsModule. I don't know what the difference is, or if one has been deprecated in favour of the other.

Yet another version, this one from 2016. https://stackoverflow.com/questions/37960045/unreal-engine-4-c-change-staticmeshcomponent-of-astaticmeshactor The goal of this code is to change the material of some Actor.

//Find Actor and change Material
AStaticMeshActor* Actor = ...;

// Material Path.
FString matPath = 
    "Material'/Game/StarterContent/Materials/M_Metal_Gold.M_Metal_Gold'";
// Material Instance.
UMaterialInstanceConstant* material = 
    Cast<UMaterialInstanceConstant>(
        StaticLoadObject(
            UMaterialInstanceConstant::StaticClass(),
            nullptr,
            *matPath));

TArray<UStaticMeshComponent*> MaterialComps;
Actor->GetComponents(MaterialComps);
for (int32 Index = 0; Index != MaterialComps.Num(); ++Index)
{
    UStaticMeshComponent* targetComp = MaterialComps[Index];
    int32 mCnt = targetComp->GetNumMaterials();
    for (int i = 0; i < mCnt; i++)
    {
        targetComp->SetMaterial(0, material);
    }
}

This one uses StaticLoadObject to get the UMaterialInstanceConstant. So a new one is not created, we re-use one that already exists. Can StaticLoadObject be used outside of constructors? Can StaticLoadObject be used during Play? Think it's "yes" to both of these. The documentation doesn't forbid it, at least.

[[2020-05-10_11:01:04]] Materials
[[2021-05-06_08:51:54]] UMaterial
[[2020-08-11_11:13:52]] UMaterialInstance
[[2020-08-11_13:53:57]] UMaterialInstanceDynamic