Gaffer — Overview

What It Is

Gaffer is a dockable Unreal Editor panel written in C++ and Slate. It replaces two Blueprint editor utility widgets — the original CameraController and LightController — with a single unified tool that handles cameras, lights, environment actors, and any actor class you register. The panel integrates directly with Sequencer to support per-property keyframing with configurable key modes, interpolation types, and track-targeting strategies. Because Gaffer is declared as an editor-only module, it compiles only for editor targets and leaves no trace in packaged builds.

The motivation for the rewrite was maintainability and capability. The Blueprint widgets had grown to hundreds of nodes each and were difficult to extend. The C++ implementation makes the same logic legible, testable, and extensible by other plugins.

Module Layout

Both modules are editor-only. The Gaffer module provides the data model and does not depend on Slate; GafferEditor owns every widget and the GafferSequencerBridge.

Architecture

graph TD
    subgraph Gaffer ["Gaffer (data model)"]
        Registry["Actor Registry"]
        Types["GafferTypes.h\nEGafferKeyMode\nEGafferInterpMode\nEGafferTrackTarget"]
        PropSet["GafferPropertySet"]
        TagReg["GafferTagRegistry"]
    end

    subgraph GafferEditor ["GafferEditor (UI)"]
        Panel["SGafferPanel\n(root dockable tab)"]
        Tree["Actor Tree\nSGafferActorTree"]
        CamInspector["Camera Inspector\nSGafferCameraInspector"]
        LightInspector["Light Inspector\nSGafferLightInspector"]
        KeyRow["SGafferKeyframePropertyRow"]
        KeyState["GafferKeyframeState"]
        Bridge["GafferSequencerBridge"]
        Bulk["GafferBulkActions"]
    end

    Registry --> Tree
    PropSet --> CamInspector
    PropSet --> LightInspector
    TagReg --> Tree
    Types --> KeyState
    KeyState --> KeyRow
    KeyRow --> CamInspector
    KeyRow --> LightInspector
    CamInspector --> Bridge
    LightInspector --> Bridge
    Tree --> Panel
    CamInspector --> Panel
    LightInspector --> Panel
    Bulk --> Panel

The root widget SGafferPanel owns the actor tree on the left and swaps in the appropriate inspector on the right depending on what is selected. GafferKeyframeState is a shared object passed down through the inspector hierarchy so that key mode, interpolation mode, track target, and the auto-key flag are consistent across every property row.

Inspector System

SGafferKeyframePropertyRow

Every keyframeable property in both the camera and light inspectors is rendered by SGafferKeyframePropertyRow. The row contains three visual zones:

1. A left circle indicator that reflects the current keyframe state of the property (no key, key at current frame, or modified since last key).
2. A label and value widget (spin box, color picker, or check box depending on type).
3. A right diamond button that triggers GafferSequencerBridge::KeyProperty for that specific property.

All rows in an inspector share the same GafferKeyframeState reference, so changing the key mode in the settings bar immediately affects every subsequent key operation in that inspector session.

Camera Inspector

The camera inspector exposes eight keyframeable properties arranged in a primary section and a collapsible Advanced section:

Primary section:

Advanced section (collapsible):

The status row at the top of the camera inspector displays the actor's class icon at 24×24 pixels, the actor label, and — when the actor is bound in an active Sequence — a green "Bound" pill.

Light Inspector

The light inspector adapts its UI to the light type of the selected actor. All light types share a base section:

A conditional Shape section renders additional controls based on light type:

A collapsible Advanced section provides:

Keyframing Pipeline

Keyframing in Gaffer follows a single path: a diamond button press (or an auto-key trigger) calls SGafferInspector::AutoKeyProperty or the row's key delegate, which invokes GafferSequencerBridge::KeyProperty. That function receives:

• The target actor
• A property name string matching the Sequencer track's property path
• The current EGafferKeyMode
• The current EGafferInterpMode
• The current EGafferTrackTarget

KeyProperty locates the correct movie scene track, creates or updates a key at the resolved frame, and sets its tangent type to match the requested interpolation mode.

Key Modes

Interpolation Modes

Track Targeting

Auto-Key

When auto-key is enabled via the settings bar toggle, every OnValueChanged callback in every property row calls SGafferInspector::AutoKeyProperty. This checks the bAutoKeyEnabled flag on the shared GafferKeyframeState and, if true, calls GafferSequencerBridge::KeyProperty immediately without a button press. Auto-key respects all other key mode, interpolation, and track-targeting settings.

Groups and Tags

Groups

A group is a named set of actors with an associated color swatch and three numeric overrides:

Groups are edited inline in the actor tree when the group row is selected. A context menu on any actor row provides "Add to Group" and "Remove from Group" submenus listing all existing groups. Groups are stored in the GafferGroupRegistry and are not saved to the Sequencer sequence — they are authoring-time organizational metadata.

Tags

Tags are free-form text labels attached to individual actors. The tag input dialog is a floating SWindow containing a single text field. Tags are stored in GafferTagRegistry keyed by actor GUID so they survive actor renames. The actor tree can be filtered to show only actors that carry a specific tag.

Custom Class Registration

By default Gaffer's actor tree shows ACineCameraActor, all ALight subclasses, and sky/atmosphere actors. Any additional AActor subclass can be registered so it appears in the tree and can have properties added to its inspector.

Registration happens in a module startup function or a plugin's StartupModule:

#include "GafferActorRegistry.h"

// Inside IModuleInterface::StartupModule or similar:
FGafferActorRegistry::Get().RegisterClass(
    AMyCustomLightRig::StaticClass(),
    FText::FromString(TEXT("Custom Light Rigs")),   // display category in the tree
    FSlateIcon(FMyStyle::GetStyleSetName(), "Icons.LightRig")
);

To also expose custom properties for keyframing, create a UGafferPropertySet subclass and register it alongside the class:

FGafferActorRegistry::Get().RegisterPropertySet(
    AMyCustomLightRig::StaticClass(),
    UMyCustomLightRigPropertySet::StaticClass()
);