UI performance

Measure first

Profile a representative screen on target hardware with Unreal Insights and Slate Insights. Record CPU time, paint/layout invalidations, widget count, construction hitches, draw elements, and memory. Apply one optimization, then re-profile.

Highest-value actions

1. Replace raw property bindings and widget Tick with events/delegates/FieldNotify.
2. Remove unused children; hidden children are still loaded and constructed.
3. Split huge screens into always-ready, preload, and asynchronously loaded sections.
4. Use ListView/TileView/TreeView for large collections. They virtualize entries and create only enough entry widgets for the visible region.
5. Reuse/pool dynamic widgets when churn is measured; clear all item state on reuse.
6. Reduce nested Canvas Panels and rich text where simpler containers/text suffice.
7. Avoid overlapping layers that create unnecessary Slate layer/draw cost.

Invalidation selector

• Global Invalidation: evaluate for broad mostly-static UI; measure project-wide behavior.
• Invalidation Box: cache a mostly-static subtree whose geometry/paint rarely changes.
• Volatile widget: isolate a widget that changes every frame inside an invalidated tree.
• Retainer Panel: flatten a subtree to a texture, optionally reducing render frequency or applying an effect; costs render-target memory and can add latency/artifacts.

Do not wrap constantly changing trees in invalidation and repeatedly destroy the cache benefit. Do not use a Retainer Panel as a generic speed button.

Construction strategy

Screen type	Strategy
Always-visible HUD	create once; push small updates
Frequent critical menu	preload or keep pooled/hidden if memory permits
Rare expensive menu	async load and release when dismissed
Long inventory	virtualized list; item objects separate from entries
Transient notifications	queue + bounded pool

Regression checks

• Open/close the screen 50 times: widget and delegate counts must stabilize.
• Scroll thousands of items: entry count should track visible rows, not item count.
• Change one field: confirm the entire tree is not invalidated unnecessarily.
• Profile editor and packaged target build; trust the representative target result.