Concept: The Chord System
A chord requires modifier keys (Shift / Ctrl / Alt) on an action. Enforcement lives in UInputTriggerCrimsonDynamicChord, an UInputTrigger that sits in an IMC mapping's Triggers array. Because it is per mapping, the same action can carry different chords in different IMCs, and 1 / Shift+1 / Ctrl+1 can be three distinct bindings on one key.
Exact-match semantics
The trigger passes only when the held modifiers exactly equal the requirement. A chord requiring Shift fails if Ctrl is also down; a chord requiring no modifiers fails while any modifier is held. This exactness is what prevents a bare 1 from firing underneath Shift+1.
UpdateState returns Triggered immediately for gamepad input - chords are a keyboard/mouse concern. A chorded keyboard mapping therefore never suppresses the same action on a controller.Reading modifier state
Each registered modifier (FCrimsonInputModifierDefinition in UCrimsonInputSettings::ModifierDefinitions) counts as held when its ModifierAction is active - read via GetActionValue, so it respects the player's own key mappings - or, when the action has no live mapping, when one of its FallbackKeys is down (AnalogThreshold decides when a gamepad trigger counts as held). Give each modifier an action so a player who remaps the modifier key still chords correctly.
Inline vs rebindable
| Inline | Rebindable | |
|---|---|---|
MappingName | empty (None) | set to a UCrimsonPlayerMappableKeySettings.Name |
| Source of the chord | DefaultChord on the trigger | player override in UCrimsonInputUserSettings, else DefaultChord |
| Player can change it | no | yes (persisted, SaveGame) |
| Who adds the trigger | you, on the IMC mapping | auto-injected by AddMappingContextWithChordTriggers (or you, for a default) |
Overrides always win over the inline DefaultChord for a rebindable mapping, so a designer default is just the starting value a player can change.
How injection works (originals stay untouched)
UCrimsonInputHelpers::CreateIMCWithChordTriggers returns a transient copy of your IMC. It walks the mappings; for any whose action uses UCrimsonPlayerMappableKeySettings and lacks a chord trigger, it adds one (with MappingName set and an empty DefaultChord). Your asset is never modified, and results are cached per source IMC. AddMappingContextWithChordTriggers is the convenience wrapper that patches then applies. This is why you must add the patched copy in place of the original - never both at once.
RequiredModifiers - Input.Modifier.* gameplay tags resolved through the modifier registry, so they follow a rebind - plus RequiredModifierKeys, raw FKey entries for projects that registered no modifiers. Both are SaveGame. The struct (Input/CrimsonChordRequirement.h) is read and written through ICrimsonInputBindingProvider (Input/ICrimsonInputBindingProvider.h), which your UEnhancedInputUserSettings subclass implements, so a settings screen edits chords through one interface. It also formats its own label via GetDisplayName(FKey, bLongDisplayName) and GetModifierPrefix().