ModContentRegistry: Filter item descriptor by resource form (#246)

In the `IsDescriptorFilteredOut()` function, add additional checks to
filter out item descriptors depending on their resource form. Without
this change, the `IncludeNonSolid` flag does absolutely nothing. Also
filter out any non-subclasses of `UFGItemDescriptor`, which shouldn't
have been registered in the item registry to begin with.

Signed-off-by: Angel Pons <th3fanbus@gmail.com>

Author: Th3Fanbus

Mods/SML/Source/SML/Private/Registry/ModContentRegistry.cpp

@@ -860,13 +860,39 @@ void UModContentRegistry::AutoRegisterRecipeReferences( TSubclassOf<UFGRecipe> R
 	}
 }
 
+static bool IsResourceFormFilteredOut(EResourceForm ResourceForm, EGetObtainableItemDescriptorsFlags Flags)
+{
+	using enum EGetObtainableItemDescriptorsFlags;
+	using enum EResourceForm;
+
+	switch (ResourceForm) {
+	case RF_INVALID:
+		return !EnumHasAnyFlags(Flags, EGetObtainableItemDescriptorsFlags(IncludeBuildings | IncludeCustomizations | IncludeVehicles | IncludeCreatures | IncludeSpecial));
+	case RF_SOLID:
+		return false;
+	case RF_LIQUID:
+	case RF_GAS:
+		return !EnumHasAnyFlags(Flags, EGetObtainableItemDescriptorsFlags(IncludeNonSolid));
+	case RF_HEAT: /* FIXME: Could be omitted, so that the default case handles it */
+		return true;
+	default:
+		return true;
+	}
+}
+
 bool UModContentRegistry::IsDescriptorFilteredOut( const UObject* ItemDescriptor, EGetObtainableItemDescriptorsFlags Flags )
 {
 	if (!ItemDescriptor) {
 		UE_LOG(LogContentRegistry, Warning, TEXT("IsDescriptorFilteredOut called with null ItemDescriptor, returning true (filtering out)"));
 		return true;
 	}
-	const auto descriptorClass = Cast<UClass>(ItemDescriptor);
+	const TSubclassOf<UFGItemDescriptor> descriptorClass = const_cast<UClass*>(Cast<UClass>(ItemDescriptor));
+	if (!descriptorClass) {
+		return true;
+	}
+	if (IsResourceFormFilteredOut(UFGItemDescriptor::GetForm(descriptorClass), Flags)) {
+		return true;
+	}
 
 	if (!EnumHasAnyFlags(Flags, EGetObtainableItemDescriptorsFlags::IncludeBuildings) && descriptorClass->IsChildOf<UFGBuildingDescriptor>()) {
 		return true;

Mods/SML/Source/SML/Public/Registry/ModContentRegistry.h

@@ -5,6 +5,7 @@
 #include "FGRecipe.h"
 #include "FGResourceSinkSubsystem.h"
 #include "Engine/DataTable.h"
+#include "Misc/EnumClassFlags.h"
 #include "ModContentRegistry.generated.h"
 
 DECLARE_LOG_CATEGORY_EXTERN(LogContentRegistry, Log, All);
@@ -140,6 +141,8 @@ enum class EGetObtainableItemDescriptorsFlags : uint8
 	Default = None,
 };
 
+ENUM_CLASS_FLAGS(EGetObtainableItemDescriptorsFlags);
+
 /**
  * Manages registration and lifetime of the modded content
  *