dtsong/motion-design

Motion Design

Purpose

Design the motion language for a feature or system, including transition specs, micro-interaction definitions, choreography principles, and reduced-motion alternatives.

Scope Constraints

Reads existing animation code, CSS transitions, and motion specifications for analysis. Does not modify source files or execute animations. Does not generate production animation code directly.

Inputs

• Feature or component requiring motion design
• Existing animation patterns in the project (if any)
• Performance constraints (target FPS, device capabilities)
• Accessibility requirements (prefers-reduced-motion support)

Input Sanitization

No user-provided values are used in commands or file paths. All inputs are treated as read-only analysis targets.

Procedure

Progress Checklist

• [ ] Step 1: Identify motion opportunities
• [ ] Step 2: Define motion principles
• [ ] Step 3: Spec each animation
• [ ] Step 4: Design choreography
• [ ] Step 5: Reduced-motion alternatives
• [ ] Step 6: Performance considerations

Step 1: Identify Motion Opportunities

Catalog where motion adds meaning:

• State transitions: Loading to loaded, collapsed to expanded, hidden to visible
• Navigation transitions: Screen push/pop, modal present/dismiss, tab switch
• Feedback responses: Button press, form submission, error shake, success check
• Attention guidance: New item appears, notification badge, scroll-to-target
• Data changes: List reorder, item add/remove, value count-up

Step 2: Define Motion Principles

Establish the motion language for this project:

• Duration scale: Micro (100ms), short (200ms), medium (300ms), long (500ms)
• Easing curves: Enter (ease-out), exit (ease-in), standard (ease-in-out)
• Stagger: Delay between sequential items (50-100ms per item, max 5 items)
• Distance: How far elements travel relative to their size

Step 3: Spec Each Animation

For each motion opportunity, define:

• Property: What changes (opacity, transform, height, color)
• Duration: How long (from the duration scale)
• Easing: Which curve (from the easing set)
• Delay: When it starts relative to the trigger
• Direction: Where it moves from/to

Step 4: Design Choreography

For multi-element transitions:

• Entrance order: What appears first, second, third
• Stagger timing: Delay between each element
• Shared elements: Elements that morph between states
• Exit choreography: Reverse of entrance, or distinct exit pattern

Step 5: Reduced-Motion Alternatives

For every animation, define the prefers-reduced-motion alternative:

• Instant transitions: Replace motion with opacity crossfade
• Remove parallax: Static positioning instead
• Simplify choreography: Single fade-in instead of staggered entrance
• Keep functional animation: Loading spinners stay (they communicate state)

Step 6: Performance Considerations

Verify motion feasibility:

• Composite-only properties: Prefer transform and opacity (GPU-accelerated)
• Avoid layout thrash: Don't animate width, height, top, left
• will-change hints: Add for elements that will animate
• 60fps budget: Each frame must complete in <16.6ms

Compaction resilience: If context was lost during a long session, re-read the Inputs section to reconstruct what feature is being designed, check the Progress Checklist for completed steps, then resume from the earliest incomplete step.

Output Format

# Motion Design Specification

## Motion Principles
| Property | Value | Usage |
|----------|-------|-------|
| Duration (micro) | 100ms | Hover, focus |
| Duration (short) | 200ms | Expand, collapse |
| Duration (medium) | 300ms | Page transitions |
| Ease (enter) | cubic-bezier(0, 0, 0.2, 1) | Elements appearing |
| Ease (exit) | cubic-bezier(0.4, 0, 1, 1) | Elements leaving |
| Stagger | 50ms | List items |

## Animation Specs

### [Component/Interaction Name]
**Trigger:** [User action or state change]
**Property:** [What changes]
**From → To:** [Start value → End value]
**Duration:** [From scale]
**Easing:** [From set]
**Reduced motion:** [Alternative]

## Choreography
### [Transition Name]
1. [Element] fades in at 0ms (200ms, ease-out)
2. [Element] slides up at 50ms (200ms, ease-out)
3. [Element] fades in at 100ms (200ms, ease-out)

## Reduced Motion Summary
| Animation | Full Motion | Reduced Motion |
|-----------|------------|----------------|
| Page enter | Slide + fade | Instant fade |
| List stagger | Staggered slide-up | Single fade |
| Loading | Spinner | Spinner (kept) |

Handoff

• Hand off to visual-audit if motion design reveals visual hierarchy issues needing interface-level critique.
• Hand off to design-system-architecture if animation tokens (durations, easings) need integration into the design token system.

Quality Checks

• [ ] Every animation has a purpose (communicates state change, guides attention, or provides feedback)
• [ ] Duration and easing values come from the defined scale, not arbitrary values
• [ ] Every animation has a prefers-reduced-motion alternative
• [ ] Animations use composite-only properties (transform, opacity) where possible
• [ ] Stagger timing doesn't exceed 5 items (cap the stagger, fade the rest)
• [ ] No animation exceeds 500ms (users perceive delays >400ms as laggy)

Evolution Notes

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