System selector

Use UMG only

Choose plain UMG when all are true:

• screen layering is simple;
• mouse/keyboard is primary or gamepad navigation is small;
• input prompts do not need automatic platform/device swapping;
• the team benefits more from a small dependency surface than CommonUI routing.

UMG remains the view layer even when CommonUI is added.

Add CommonUI

Choose CommonUI when one or more are load-bearing:

• multiple stacked screens or modal layers;
• controller-first focus and cardinal navigation;
• a universal back action;
• platform-specific button glyphs or runtime input-method switching;
• selective input routing between overlapping UI layers.

CommonUI is an extensive paradigm, not a general requirement. Epic specifically identifies complex multi-layered and cross-platform interfaces as its main use cases.

Choose the update model

Need	Preferred mechanism	Note
Small explicit screen	Delegates/events + widget setters	Stable and easy to trace
Reusable presentation model	Viewmodel + FieldNotify	MVVM is Beta in UE 5.8
One-time construction data	Expose-on-spawn/init function	Do not poll it
Per-frame visual motion	UMG animation/material/limited Tick	Profile and isolate

Do not use raw property/function bindings as the default; they poll and can have a large performance impact. Do not adopt Beta MVVM without documenting fallback and platform testing.

UE 5.8 input choice

UE 5.8 release notes describe unification of Enhanced Input and Common Input/UI, including removing duplicate data assets. Prefer Enhanced Input Actions and metadata for new 5.8 work. Treat older CommonUI action Data Tables as a legacy-compatible path, not the default new design.

Related Constitution principles

• GDC-L1-UX-0002: reveal complexity progressively.
• GDC-L1-UX-0003: make the interface communicate.
• GDC-L1-UX-0006: build accessibility in early.
• GDC-L1-ARCH-0003: decouple cross-system reactions through events.
• GDC-L1-ARCH-0006: distinguish authoritative from transient state.