Toggle the sky — click it or focus and press Space.

{night ? "night · moon risen" : "day · sun up"}

); } ``` ## Accessibility & performance Honors `prefers-reduced-motion` with a designed static frame or fade (never a blank box) and passes `className` through. ## Source (`meridian.tsx`) ```tsx "use client"; import { animate, motion, useMotionValue, useTransform } from "motion/react"; import * as React from "react"; import { useReducedMotion } from "@/hooks/use-reduced-motion"; import { cn } from "@/lib/utils"; export interface MeridianPalette { /** Top sky gradient stop. */ skyTop: string; /** Bottom sky gradient stop. */ skyBottom: string; /** Celestial body core color (sun in day, moon in night). */ body: string; } export interface MeridianProps extends Omit, "onChange"> { /** Controlled night state — `true` is night/dark. */ checked?: boolean; /** Initial night state when uncontrolled. @default false */ defaultChecked?: boolean; /** Fires on every toggle with the next night state. */ onChange?: (checked: boolean) => void; /** Size multiplier applied to the whole diorama. @default 1 */ scale?: number; /** * Seconds the arc + scene transition takes (spring visual duration). * @default 0.6 */ duration?: number; /** Stars that ignite, staggered, once the moon seats. @default 7 */ starCount?: number; /** Clouds that drift in the day sky. @default 3 */ cloudCount?: number; /** Day palette overrides — warm sun on blue sky. */ dayColors?: Partial; /** Night palette overrides — cool moon on indigo sky. */ nightColors?: Partial; /** Accessible label for the switch. @default "Toggle dark mode" */ label?: string; } const DAY_DEFAULT: MeridianPalette = { skyTop: "#3aa0e8", skyBottom: "#a6d9f6", body: "#ffd24d", }; const NIGHT_DEFAULT: MeridianPalette = { skyTop: "#111033", skyBottom: "#2b2a5e", body: "#e7ecfb", }; /** Warm sunset band that peaks at mid-track as the two palettes cross. */ const DUSK_TOP = "#f0955a"; const DUSK_BOTTOM = "#6d5a9c"; /** Deterministic PRNG so scatter is identical on server and client. */ function mulberry32(seed: number): () => number { let a = seed >>> 0; return () => { a |= 0; a = (a + 0x6d2b79f5) | 0; let t = Math.imul(a ^ (a >>> 15), 1 | a); t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t; return ((t ^ (t >>> 14)) >>> 0) / 4294967296; }; } interface Star { left: number; top: number; size: number; cross: boolean; twinkleDur: number; twinkleDelay: number; } interface Cloud { top: number; left: number; w: number; driftDur: number; driftDelay: number; } /** * Meridian — a day/night theme switch built as a miniature diorama. The track * is a sky and the thumb is the celestial body: toggling sends the sun setting * and the moon rising along a shallow meridian arc that dips at mid-track while * the sky crossfades day-blue → dusk → night-indigo. Clouds drift out ahead of * the moon; stars ignite in a staggered scatter once it seats. A real * `role="switch"` with keyboard toggle; the arc runs on transform only. * Reduced motion collapses to an instant scene swap — no arc, no twinkle. */ export function Meridian({ checked, defaultChecked = false, onChange, scale = 1, duration = 0.6, starCount = 7, cloudCount = 3, dayColors, nightColors, label = "Toggle dark mode", className, style, disabled, ...rest }: MeridianProps) { const reducedMotion = useReducedMotion(); const isControlled = checked !== undefined; const [internal, setInternal] = React.useState(defaultChecked); const on = isControlled ? checked : internal; const day = { ...DAY_DEFAULT, ...dayColors }; const night = { ...NIGHT_DEFAULT, ...nightColors }; // Geometry (px), all driven off the size multiplier. const S = scale; const W = 92 * S; const H = 40 * S; const PAD = 4 * S; const THUMB = H - PAD * 2; const TRAVEL = W - THUMB - PAD * 2; const DIP = reducedMotion ? 0 : H * 0.16; // Single spring drives the whole scene; every layer derives from it, so the // arc, crossfade, and body swap stay locked in phase. const progress = useMotionValue(on ? 1 : 0); React.useEffect(() => { // Reduced motion: snap instantly to the target (visualDuration:0 on a spring // still resolves over several frames — it must be an immediate set, so the // scene swaps with no arc/dusk/star-ignition, per the a11y contract). if (reducedMotion) { progress.set(on ? 1 : 0); return; } const controls = animate(progress, on ? 1 : 0, { type: "spring", visualDuration: duration, bounce: 0.28, }); return controls.stop; }, [on, reducedMotion, duration, progress]); const x = useTransform(progress, [0, 1], [0, TRAVEL]); const yArc = useTransform(progress, [0, 0.5, 1], [0, DIP, 0]); const dayOpacity = useTransform(progress, [0, 1], [1, 0]); const nightOpacity = useTransform(progress, [0, 1], [0, 1]); const duskOpacity = useTransform(progress, [0, 0.5, 1], [0, 0.85, 0]); const sunOpacity = useTransform(progress, [0, 0.55], [1, 0]); const moonOpacity = useTransform(progress, [0.45, 1], [0, 1]); const glowDay = useTransform(progress, [0, 1], [0.55, 0]); const glowNight = useTransform(progress, [0, 1], [0, 0.5]); const stars = React.useMemo(() => { const rnd = mulberry32(0x51a2 + starCount); return Array.from({ length: Math.max(0, starCount) }, () => { const rx = rnd(); const ry = rnd(); return { left: 8 + rx * 82, top: 12 + ry * 52, size: (1.4 + rnd() * 1.8) * S, cross: rnd() > 0.62, twinkleDur: 1.8 + rnd() * 2.2, twinkleDelay: rnd() * 1.5, }; }); }, [starCount, S]); const clouds = React.useMemo(() => { const rnd = mulberry32(0xc10d + cloudCount); return Array.from({ length: Math.max(0, cloudCount) }, () => ({ top: 22 + rnd() * 34, left: 30 + rnd() * 42, w: (14 + rnd() * 12) * S, driftDur: 7 + rnd() * 5, driftDelay: rnd() * 3, })); }, [cloudCount, S]); const seatDelay = reducedMotion ? 0 : duration * 0.62; const starStagger = reducedMotion ? 0 : duration * 0.14; const toggle = React.useCallback(() => { if (disabled) return; const next = !on; if (!isControlled) setInternal(next); onChange?.(next); }, [disabled, on, isControlled, onChange]); return ( ); } ```