Case study: migrating Epic's Action RPG (4.27 to 5.8)

Action RPG is Epic's free C++ sample game built on the Gameplay Ability System. It is a good test: C++ modules, Gameplay Abilities, many Cascade effects, mobile settings and a loading screen module. This page follows a complete unattended migration from 4.27 to 5.8 with UEAPM and shows the real numbers from its report.

1. Get the sample

1. In the Epic Games Launcher, open Unreal Engine > Samples and download Action RPG for engine 4.27.
2. Create a project from it (for example ActionRPGSampleUE427).
3. Make a copy of the project folder. Leave out Binaries, Intermediate, Saved and DerivedDataCache. All the following steps work on the copy.

2. File steps from a 5.8 project

The project cannot open in 5.8 yet: its C++ does not compile. Run the project and cpp steps from any 5.8 project that has UEAPM, pointed at the copy:

powershell -File Tools\migrate_headless.ps1 -Project D:\Host\UeapmHost.uproject `
    -Target D:\Work\ActionRPG58\ActionRPGSampleUE427.uproject -Steps project,cpp

Result of this pass (Saved/UEAPM/History/ keeps it):

Step	Changes	Open items
project	27	1 (Manual)
cpp	8	0

• Project: engine association 4.27 to 5.8; WindowsNoEditor / MacNoEditor renamed; 11 plugin entries removed (PhysX-, VR-, Magic Leap- and LPV-related plugins among others); 13 Android and iOS settings updated for 5.8. One Manual item: the removed SlateRemote plugin.
• C++: 46 source files scanned, 7 fixes plus regenerated project files:
  • build settings V2 to V7 with the 5.8 include order, in both targets;
  • an AbilitySystemLog.h include added;
  • two ability-task checks updated for the component's weak pointer;
  • an EventData.Target access updated for object pointers;
  • GetReferencerName added to the loading screen's FGCObject.

3. Build

Run the build command printed in the report's C++ Notes:

& "C:\Program Files\Epic Games\UE_5.8\Engine\Build\BatchFiles\Build.bat" ActionRPGEditor Win64 Development `
    -Project="D:\Work\ActionRPG58\ActionRPGSampleUE427.uproject" -WaitMutex

The project builds on 5.8 with no further source changes.

4. Install UEAPM into the project

Copy the plugin to ActionRPGSampleUE427/Plugins/UnrealEngineAbsoluteProjectMigrator/ and build again.

5. Run the migration

Open the project and run the default steps from Window > Absolute Project Migrator, or unattended:

powershell -File Tools\migrate_headless.ps1 -Project D:\Work\ActionRPG58\ActionRPGSampleUE427.uproject -Editor

Summary table of this run:

Step	Status	Changes	Left (error/manual)	Warnings	Time (s)
Project and config	ran	3	0	0	0.0
Assets resave	ran	873	0	0	14.1
Blueprints	ran	0	1	0	8.6
Enhanced Input (opt-in)	not selected	0	0	0	0.0
Cascade to Niagara	ran	75	0	11	78.5
C++ source	ran	1	0	0	10.7
Rendering and mobile	ran	6	0	0	0.1
Physics (PhysX to Chaos)	ran	10	0	0	0.0

In numbers:

• 873 packages resaved in the 5.8 format, no load errors.
• 26 Cascade systems converted to Niagara, and 49 references replaced: 33 anim notifies, 9 emitters placed in maps, 4 Blueprint components and 3 spawn nodes.
• 11 warnings for references it could not replace (9 custom Trail notifies, 1 SpawnEmitterAttached call on BP_WeaponSpider, 1 Level Sequence). They keep playing Cascade, which still works in 5.8.
• 19 config changes in this pass: 3 packaging denylist keys, 6 rendering settings (including the mobile values that keep Lumen and Virtual Shadow Maps off) and 10 PhysX-era physics settings removed.
• The SlateRemote item of the first pass was resolved by the rerun of the project step: that run found nothing left to do (reruns are idempotent).
• 179 Blueprints compiled, 1 with errors: the only open item.

6. Read the report

The single open item in Left to do:

Severity	Category	Location	Fix (short)
Error	Compile error	GA_GoblinRange01	UE5 Gameplay Abilities require a cooldown Gameplay Effect to grant tags. Either set CooldownGameplayEffectClass to None or give the effect a Grant Tags component with a Cooldown.* tag.

Following the report, open GA_GoblinRange01 and set CooldownGameplayEffectClass to None. Compile and save.

Verified result

• The C++ project builds with Build.bat on 5.8.
• 179 Blueprints compile with 0 errors after the manual fix.
• All 4 maps load.
• Play In Editor from the main menu into the level works: the intro plays, the player character spawns, moves and activates melee attacks, and the converted Niagara effects play.
• Total unattended migration time: about 4 to 6 minutes on the test machine (both migration passes and the builds).