ue-slate

name	ue-slate
description	Domain knowledge for UE Slate — the C++ UI DSL, style registration system, widget ownership model, and common footguns. Use when an agent reads, reviews, or documents Slate code.
axis	domain

UE Slate Domain Knowledge

Slate is Unreal Engine's C++ immediate-mode-style UI framework. It uses a fluent declarative syntax for widget construction and a name-keyed style registration system for theming.

Widget Construction

Widgets are built with SNew(SMyWidget) (returns TSharedRef<SMyWidget>) or SAssignNew(Ptr, SMyWidget) (also assigns to an external TSharedPtr). Arguments are declared in the widget class via macros:

• SLATE_ARGUMENT(Type, Name) — value-only, stored directly
• SLATE_ATTRIBUTE(Type, Name) — TAttribute<Type>, accepts value or delegate/lambda
• SLATE_EVENT(DelegateType, Name) — delegate binding
• SLATE_STYLE_ARGUMENT(StyleType, Name) — const StyleType*, raw pointer to a style struct from a registered style set

Compound widgets own a single ChildSlot populated via operator[]. Panel widgets (SVerticalBox, SHorizontalBox, etc.) use AddSlot() / operator+.

Style System

Registration

FSlateStyleSet implements ISlateStyle. A module registers its styles at startup:

1. Construct: FSlateStyleSet StyleSet(FName("MyStyleName"))
2. Set content root: SetContentRoot(...) — base path for brush macros (IMAGE_BRUSH, BOX_BRUSH, etc.)
3. Populate: Set(FName, ...) overloads for brushes, fonts, colors, margins, floats, sounds, and FSlateWidgetStyle subclasses
4. Register: FSlateStyleRegistry::RegisterSlateStyle(StyleSet)
5. Unregister in ShutdownModule() — the style set must outlive all widgets referencing it

Lookup

ISlateStyle provides typed getters keyed by FName:

• GetBrush / GetOptionalBrush — GetBrush logs a warning and returns a pink placeholder on miss; GetOptionalBrush returns a default silently
• GetFontStyle, GetColor, GetSlateColor, GetMargin, GetFloat, GetSound
• GetWidgetStyle<T>(Name) / HasWidgetStyle<T>(Name) — templated on FSlateWidgetStyle subclasses

All getters accept an optional Specifier string that is appended to the name, enabling style variants (e.g. "Button.Primary", "Button.Danger").

Parent style fallback (SetParentStyleName) resolves at query time via FSlateStyleRegistry. If the parent isn't registered yet, fallback silently returns nothing.

Global Access

• FSlateStyleRegistry::FindSlateStyle(FName) — returns const ISlateStyle* or nullptr
• FAppStyle::Get() — the application-wide default style set

Widget Ownership

• TSharedRef<SWidget> / TSharedPtr<SWidget> are the ownership primitives. A widget held only in a parent slot is destroyed with the parent.
• An external TSharedPtr kept after parent destruction points to a widget that may have been removed from the tree — it won't null out automatically. Use SAssignNew deliberately when you need to retain a handle.
• SLATE_STYLE_ARGUMENT stores a raw const* to the style struct. The pointed-to memory must be owned by a live registered style set for the widget's entire lifetime.

Footguns

• Name typos are silent runtime failures. Style lookups are string-keyed with no compile-time validation. A mistyped name returns a pink placeholder brush or zero-value default with only a log warning.
• Registration ordering matters. Styles must be registered before any widget that references them is constructed. Module startup order is the typical failure point.
• Brush ownership is caller-new. Set(FName, new IMAGE_BRUSH(...)) stores the raw pointer. If the style set is destroyed while widgets still reference the brush, the next paint frame crashes.
• FVector2D is deprecated for brush size arguments. Use FVector2f.