design-engineering

# design-engineering In a world where most software works well enough, feel is the differentiator. Most of what makes an interface feel right is detail the user never consciously notices - the aggregate of small correct choices. Build for that aggregate. ## Motion decision framework Answer these in order before writing any animation. ### 1. Should it animate at all? The deciding factor is frequency. The more often a user sees it, the less it should move. | How often the user sees it | Decision | |----------------------------|----------| | 100+ times/day (shortcuts, command palette) | No animation, ever | | Tens of times/day (hover, list nav) | Remove or drastically reduce | | Occasional (modals, drawers, toasts) | Standard animation | | Rare or first-time (onboarding, celebration) | Room for delight | Never animate a keyboard-initiated action. It repeats all day; animation makes it feel slow and disconnected from the keypress. ### 2. What is the purpose? Every animation needs an answer to "why does this move?" Valid ones: spatial consistency (enters and exits the same edge), state change, feedback (a press that confirms the interface heard you), or preventing a jarring appear/disappear. "It looks cool" is not a purpose for anything the user sees often. ### 3. What easing? - Entering or exiting -> `ease-out` (fast start, feels responsive). - Moving or morphing on screen -> `ease-in-out`. - Hover or color change -> `ease`. - Constant motion (marquee, progress) -> `li...