Reduce Motion Settings

Relevant source files

The following files were used as context for generating this wiki page:

• Sources/SwiftDitherKit/DitherMotion.swift
• Sources/SwiftDitherKit/SwiftDitherKit.docc/InteractionAndAccessibility.md
• Sources/SwiftDitherKit/DitherRasterView.swift
• Tests/SwiftDitherKitTests/DitherMotionTests.swift
• Sources/SwiftDitherKit/DitherSparkles.swift
• Examples/MotionDemo/MotionDemo/MotionDemoView.swift

Reduce Motion Settings in SwiftDitherKit ensure that chart visualizations remain accessible and usable for users who prefer or require limited screen movement. The system detects the system-wide accessibilityReduceMotion setting to alter how transitions, effects, and idle animations are rendered.

When Reduce Motion is active, complex spatial animations—such as sliding leading reveals or radial scaling—are replaced by simple opacity fades. Additionally, high-frequency visual effects like blinking "sparkles" are stabilized to a steady state to prevent potential triggers or distractions.

System Architecture and Logic

The motion system is governed by a set of decision-making structures that evaluate the current state of the UI against system preferences. The DitherRasterMotionDecision engine determines whether to perform a full animation, a crossfade, or an immediate replacement based on changes in data, selection, or accessibility settings.

Motion Decision Logic

The system evaluates transitions between DitherRasterMotionState instances. If the reduceMotion flag changes between states, the system triggers a "settle" action to immediately align the view to the final state using a shortened duration.

Key Motion Components

Component	Description
DitherMotion	Static utility providing specialized Animation curves and duration constants.
DitherRasterMotionState	A Sendable struct capturing checksums, tokens, and the current reduceMotion preference.
DitherRasterMotionDecision	An enumeration defining transition types: none, replace, crossfade, replay, and settle.
DitherRasterTransitionProgress	Tracks the interpolation values (entrance and update) for GPU-accelerated reveals.

Sources: DitherMotion.swift:7-73, DitherRasterView.swift:15-25

Visual Adjustments in Reduced Motion

When reduceMotion is enabled, the visual output is modified across three primary areas: transitions, masking effects, and idle animations.

1. Transitions and Blurs

Standard transitions in SwiftDitherKit often involve a "transition blur." With Reduce Motion, this blur is completely removed (set to 0) to avoid processing-heavy or visually distracting smearing effects.

• Standard Updates: Use updateDuration (0.22s).
• Reduced Motion Updates: Use reducedMotionDuration (0.14s).
• Blur Calculation: reduceMotion ? 0 : clamped(progress) * transitionBlur.

Sources: DitherMotion.swift:10-37, DitherMotionTests.swift:16-27

2. Reveal and Scale Effects

Different chart types utilize specific reveal styles. Reduce Motion forces these styles to rely exclusively on opacity rather than spatial movement.

Reveal Style	Standard Behavior	Reduced Motion Behavior
leading	Horizontal wipe (Cartesian charts)	Opacity fade
angular	Clockwise wipe (Pie charts)	Opacity fade
radial	Scaling from 0.96 to 1.0 (Radar charts)	Opacity fade (No scaling)

Sources: DitherRasterView.swift:155-163, DitherRasterView.swift:293-315, DitherMotion.swift:30-32

3. Idle Sparkle Stabilization

Area and line charts typically display "sparkles" that twinkle based on a sine wave calculation. When motion is reduced, these sparkles stop blinking.

Implementation Details

The DitherAnimatedRaster view synchronizes these settings using the @Environment(\.accessibilityReduceMotion) property wrapper.

// Example of motion synchronization logic
@MainActor
private func synchronizeMotion(to next: DitherRasterMotionState) async {
  let decision = DitherRasterMotionDecision.decide(from: lastMotionState, to: next)
  lastMotionState = next

  switch decision {
  case .settle:
    previousFrame = nil
    progress.update = 1
    withAnimation(DitherMotion.reduced) {
      progress.entrance = 1
    }
  // ... other cases
  }
}

Sources: DitherRasterView.swift:85-115, MotionDemoView.swift:4-10

Summary of Reduced Motion Logic

The system ensures that an interrupted entrance or a mid-animation toggle of the Reduce Motion setting does not leave replacement content masked out. The settle() function is called to immediately force entrance and update progress to 1, ensuring visual consistency.

Sources: DitherMotion.swift:69-73, DitherMotionTests.swift:57-73, InteractionAndAccessibility.md:38-40