Interactable Grab Object Implementation

Core Components:

• Assets/_MolcaSDK/_VR/Scripts/Scenario/Steps/GrabStep.cs — Step that validates grab completion
• Assets/_MolcaSDK/_VR/Scripts/Scenario/Steps/Auxiliary/StepObjectHighlightAuxiliary.cs — Highlights objects while step is active
• Assets/_MolcaSDK/_VR/Scripts/Scenario/Listener/StepDirectionBeltController.cs — Controls direction belt visual guidance

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When to use

Interactable Object — use this guide when implementing this interaction pattern in a VR training scenario.

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Role

This guide covers implementing a grabbable object in VR training scenarios with complete visual feedback:

• XRGrabInteractable — Core grab mechanics from XR Interaction Toolkit
• Object Highlight — Visual feedback via StepObjectHighlightAuxiliary (material overlay)
• Direction Belt — Animated guide via StepDirectionBeltController (reference-based targeting)
• GrabStep — Step completion validation and grab rules

Combined, these create a guided grab experience with clear visual feedback at each interaction stage. The auxiliaries handle visual feedback automatically through the step system—no custom scripting required for basic implementation.

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Setup Steps

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1. Create Grabbable Object with XRGrabInteractable

1. Create or select your grabbable object GameObject
2. Add XRGrabInteractable component (from XR Interaction Toolkit)
3. Configure in Inspector:
   • Select Mode: Single for one-hand grab
   • Movement Type: Instantaneous, Kinematic, or VelocityTracking (depending on physics)
   • Throw on Detach: Enable if object should move after release
   • Smooth Position/Rotation: Adjust for grabbing feel

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2. Add GrabStep for Completion Validation

1. Add GrabStep component to the grabbable object (same GameObject as XRGrabInteractable)
2. Configure in Inspector:
   • Grab Interactable: Auto-found or manually assign the XRGrabInteractable
   • Auto Find Interactable: Check to auto-discover on same object
   • Complete On Grab: Enable if step should complete immediately on grab
   • Require Hold Duration: Enable with minGrabDuration (in seconds) for timed grabs
   • Allow Any Interactor: Check to allow any hand, or assign Required Interactor (left/right)

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3. Add StepObjectHighlightAuxiliary for Visual Feedback

1. On the GrabStep component, expand Auxiliaries section
2. Click Add Auxiliary → VR/Object Highlight
3. Configure StepObjectHighlightAuxiliary:
   • Targets: Drag the grabbable object (or objects) to highlight
   • Highlight Material: Assign an emissive or outline material (acts as overlay or rim light)
   • Use Mat Swap Mode (new): Enable for material-swap-only approach (recommended for performance)
   • Deactivate Original Renderers: Check to hide original while highlight shows (copy mode only)
   • Copy Child Meshes: Check to include child objects in highlight (copy mode only)

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Highlight Modes

StepObjectHighlightAuxiliary supports two distinct approaches: Recommendation: Use Material Swap Mode (useMatSwapMode = true) for most grab interactions. Enable Copy Mode only if your highlight material requires the original geometry preserved (rare). Highlight Material Requirements:

• Copy Mode: Emissive shader with _EmissionIntensity or _Color control; outline shader (e.g., Quick Outline)
• Material Swap Mode: Rim light shader with pulse animation (e.g., mat_Highlight_Pulse); automatically copies texture properties from original (_BaseMap, _BumpMap, _Metallic, etc.)

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4. Add StepDirectionBeltController for Grab Guidance

1. On the GrabStep component, in Auxiliaries section
2. Click Add Auxiliary → VR/Scenario/Direction Belt Controller
3. Configure StepDirectionBeltController:
   • Direction Belt Ref: Assign the DirectionBelt’s ReferenceableComponent (scene must have one)
   • Target Ref: Assign the target grab point’s ReferenceableComponent
   • Use Target Position: Check to use fixed position instead of transform
   • Target Position: Set X/Y/Z coordinates if using position mode
   • Clear On End: Check to clear belt when step completes
   • Auto Complete On Target Set: Leave unchecked (GrabStep handles completion)

Important: Both directionBeltRef and targetRef require ReferenceableComponent:

• Add ReferenceableComponent to DirectionBelt GameObject (auto-generates stable ID via OnValidate)
• Add ReferenceableComponent to target grab point GameObject
• The reference system resolves these async on step start

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How It Works

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StepObjectHighlightAuxiliary

File: Assets/_MolcaSDK/_VR/Scripts/Scenario/Steps/Auxiliary/StepObjectHighlightAuxiliary.cs Highlights target objects using one of two performance-optimized approaches:

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Copy Mode (Default)

1. On step start (OnStepBegin): Creates visual copy of target objects
2. Material application: Copies all renderers to highlight duplicates with highlight material applied
3. Original renderers: Optionally deactivates originals (if Deactivate Original Renderers enabled)
4. On step end: Destroys highlight copies and restores originals
5. Cleanup: VisualCopyUtility.RestoreRenderers() re-enables deactivated renderers

Key fields (Copy Mode):

• targets[] — Objects to highlight (can be multiple)
• highlightMaterial — Material overlay (emissive/outline shader)
• deactivateOriginalRenderers — Hide originals during highlight
• copyChildMeshes — Include child meshes in the visual copy

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Material Swap Mode (Recommended) ⭐

1. On step start (OnStepBegin): Swaps renderers directly to highlight material
2. Property copying: Automatically copies texture & material properties from original to highlight via MaterialPropertyBlock:
   • Textures: _BaseMap, _BumpMap, _MetallicGlossMap, _OcclusionMap, _DetailAlbedoMap, _DetailNormalMap, _EmissionMap
   • UV Scale/Offset: _BaseMap_ST, _BumpMap_ST, _MetallicGlossMap_ST
   • Colors: _BaseColor, _Color, _EmissionColor
   • Floats: _Metallic, _Smoothness, _OcclusionStrength, _BumpScale
3. PropertyBlock pooling: Uses MaterialPropertyBlockPool to reuse blocks (zero GC allocation after warmup)
4. On step end: Restores original materials and returns pooled blocks

Key fields (Material Swap Mode):

• targets[] — Objects to highlight (can be multiple)
• highlightMaterial — Rim light material with pulse animation (e.g., mat_Highlight_Pulse)
• useMatSwapMode — Enable this toggle to activate material swap mode

Performance Characteristics:

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StepDirectionBeltController

File: Assets/_MolcaSDK/_VR/Scripts/Scenario/Listener/StepDirectionBeltController.cs Controls a DirectionBelt component to guide grab approach:

1. On step start (OnStepBegin): Resolves DirectionBelt and target references
2. Sets target: Via DirectionBelt.SetTarget(transform) or SetTargetPosition(vector3)
3. Belt animation: DirectionBelt handles visual animation (arrows, rotation, etc.)
4. On step end: Clears target if Clear On End enabled

Key fields:

• directionBeltRef — Reference to DirectionBelt ReferenceableComponent
• targetRef — Reference to grab point ReferenceableComponent
• useTargetPosition — Use fixed position instead of transform
• targetPosition — X/Y/Z position (if using position mode)
• clearOnEnd — Clear belt when step completes
• autoCompleteOnTargetSet — Auto-complete step (usually disabled)

DirectionBelt Requirements:

• Must have ReferenceableComponent for reference system
• Handles its own animations and visuals
• Scene must have DirectionBelt active (or fallback auto-find applies)

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MaterialPropertyBlockPool (Material Swap Mode Support)

File: Packages/com.molca.core/Runtime/Utilities/MaterialPropertyBlockPool.cs When Material Swap Mode is enabled, StepObjectHighlightAuxiliary uses a lightweight object pool to reuse MaterialPropertyBlock instances across highlight operations. This eliminates GC allocation overhead during frequent highlighting. Pool Behavior:

• Get() — Returns cached block or creates new (up to 100 max)
• Return() — Puts block back in pool for reuse
• Warmup() — Pre-allocates 10 blocks during initialization
• GetStats() — Returns pool diagnostics (active, pooled, total)
• Clear() — Empties pool on shutdown

Expected Performance Improvement:

• Initial (no warmup): ~100 bytes allocation per highlight
• After warmup: ~0 bytes allocation (blocks reused)
• Net improvement: ~90% GC reduction in highlight-heavy scenes

Initialization (Optional, recommended): The pool automatically warms up via MaterialPoolInitializer subsystem during app bootstrap. No additional configuration needed.

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Expected Results & Interaction Flow

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Idle State

Step is not active. Object appears in its base state (no highlight, no direction belt). The trainee sees a normal scene object with no visual cues.

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Step Activated (Initial)

When GrabStep becomes active (e.g., sequence step begins):

• Object Highlight overlay appears immediately on target object (bright or glowing based on highlight material)
• Direction Belt becomes visible, showing animated guidance toward grab point
• Visual feedback signals “this object is interactive”

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Approaching (Hand Near)

As trainee hand approaches within grab range:

• Direction Belt continues guiding toward target (arrows, rings, or belt rotation)
• Object Highlight remains visible and locked (confirming grab point)
• Visual feedback is consistent and strong

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Grabbable (In Range & Ready)

Hand is within grab range and all GrabStep conditions are met:

• Both Object Highlight and Direction Belt remain active
• Highlight material shows full intensity
• Visual feedback indicates “you can grab now”

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Grabbing (Grip Active)

Trainee presses grip trigger/button:

• Object Highlight remains locked in active state
• Direction Belt may pulse or animate (design-dependent)
• Grab is active; if hold duration required, feedback stays until timer done

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Step Complete

Grab completion conditions met (grab + hold time satisfied):

• Object Highlight fades out (if original renderers deactivated, they restore)
• Direction Belt clears (if Clear On End enabled)
• Step fires OnStepEnd event
• Visual feedback returns to idle

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Implementation (Inspector Only)

For basic grab with visual feedback, no code required. Configure entirely in Inspector:

1. XRGrabInteractable — Grab mechanics
2. GrabStep — Completion validation
3. StepObjectHighlightAuxiliary — Visual feedback (material overlay)
4. StepDirectionBeltController — Grab guidance (belt animation)

All auxiliaries are StepAuxiliary subclasses that fire automatically on step lifecycle events.

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Troubleshooting

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Material Swap Mode Setup Guide

When using Material Swap Mode for optimal performance:

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Step 1: Create or Assign Highlight Material

Use a rim light material with pulse animation:

• Recommended: Assets/_MolcaSDK/_VR/3D/Materials/mat_Highlight_Pulse.mat
• Shader: InteractablePulse.shadergraph (URP Lit base with rim light + pulse nodes)
• Properties:
  • _EnablePulse — Toggle pulse on/off
  • _PulseSpeed — Breathing rate (default: 2.0)
  • _RimColor — Glow color (default: cyan)

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Step 2: Configure StepObjectHighlightAuxiliary

1. Enable Use Mat Swap Mode toggle
2. Leave Deactivate Original Renderers unchecked (not needed for swap mode)
3. Leave Copy Child Meshes unchecked (swap mode handles all renderers automatically)
4. Assign your highlight material to Highlight Material field

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Step 3: Verify Texture Property Copying

Material Swap Mode automatically copies these from original to highlight:

• ✅ Base texture (_BaseMap / _MainTexture)
• ✅ Normal map (_BumpMap / _NormalMap)
• ✅ Metallic/Gloss map (_MetallicGlossMap)
• ✅ UV scale/offset (_BaseMap_ST, etc.)
• ✅ Roughness, metallic, smoothness values
• ✅ Custom colors (_BaseColor, _EmissionColor)

No manual property assignment needed—highlighting preserves original material appearance.

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Related

• GrabStep — Completion rules, hold duration, and position validation
• StepObjectHighlightAuxiliary — Material overlay highlight feedback (copy & swap modes)
• InteractablePulse Shader — Rim light with pulse animation
• MaterialPropertyBlockPool — Object pool for material properties (GC optimization)
• StepDirectionBeltController — Direction belt animation and targeting
• VR step auxiliaries — Overview of all StepAuxiliary types (haptics, scoring, mode events)
• Step scoring auxiliary — Grab timing and accuracy scoring
• VR player manager — Disable locomotion during precision grabs

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Visual Examples

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Scene Setup

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Interaction Flow Animation