Clyune Component GalleryLightning · How it works & code
Lightning generated by midpoint offset fractal.
Runtime logic
Visiting `/canvas/lightning`, DemoHost lazy-loads `demos/kits/kit-canvas.js` (registry `mod: 'kit-canvas'`) and calls `mount(host, { variant: 'lightning' })`. mount resolves the variant to family `lightning`; `withControls` builds the control panel (3 presets + sliders). `createCanvasStage` creates the `<canvas>` (HiDPI ≤ 2×, ResizeObserver) and the info panel. The family’s `build(S)` initialises state and returns the per-frame callback. Every `requestAnimationFrame`: read controls, advance a speed-scaled clock (dt ≤ 50 ms), run the frame callback; returned readouts go to the info panel. Pointer down/drag/move updates the interaction (drag handles, hover readouts); when untouched and auto-demo is on, the pointer follows a Lissajous path. Changing parameters: colour/speed/size apply live; structural ones remount; leaving the page cancels rAF, removes listeners and frees resources.
Environment
Canvas 2D: 2D canvas drawing; requestAnimationFrame: Display-synced animation loop; ResizeObserver: Canvas follows container size; Pointer Events: Unified mouse/touch/pen events; devicePixelRatio: Crisp HiDPI rendering (capped at 2×) · react 18.3.1, react-router-dom 6.30.6, vite 5.4.21
Dependencies
react 18.3.1
Imported APIs
withControls — Wraps the demo in the shared control panel (presets, sliders, reset); hot-updates or remounts on change; paramsFromSpec — Turns the spec (colour/speed/size/count/extras) into control-panel parameter definitions; createCanvasStage — Shared Canvas 2D stage: canvas + info panel, HiDPI, one rAF loop, pointer state, idle auto-pointer; rng — Seeded deterministic PRNG (same seed, same result); hexRgb — Colour string → [r, g, b]; rgba — Builds an rgba() colour string; clamp — Clamps a value to a range; TAU — Constant 2π; fmt — Number formatting (fixed decimals); F — Formula block HTML; S.onDown — Pointer down; S.clear — Clears with the background colour (translucent = trails); S.get — Reads current control values; S.onFrame — Registers a per-frame callback; its return value feeds the info panel; ctx.fillRect() — Fills a rectangle; ctx.beginPath() — Starts a new path; ctx.moveTo() — Moves the pen without drawing; ctx.lineTo() — Adds a straight line to a point; ctx.stroke() — Strokes the current path; ctx.arc() — Adds a circular arc (center, radius, start/end angle); ctx.fill() — Fills the current path
Source code
frontend/src/demos/kits/kit-canvas.js: FAM.lightning (L881-L931)
Code walkthrough
L883-883: Control definitions (colour/speed/size/count/extras): Lightning Color, Main Stem Thickness, Subdivision Layers n, Roughness r, Fork Probability, Strike Interval s. L884-884: Preset buttons: name → parameter overrides (3). L885-893: Info-panel content: live rows(v), formula, notes, params, steps. L894-930: Init function: sets up state and returns the per-frame callback: registers pointer handlers `S.onDown`; draws with Canvas 2D `fillRect`, `beginPath`, `moveTo`, `lineTo`, `stroke`, `arc` …; math via `Math.hypot`, `Math.atan2`, `Math.cos`, `Math.sin`, `Math.round`, `Math.max` …; returns readouts `n`, `seg`, `d0`, `br`, `L`, `r`, `hits` … to the info panel.
Principles
Take Line Segment Points M, Offset Vertically δ ~ U(−d, d) Disaggregated level d d d · r(r = roughness) n Backwards 2ⁿ segment;fork: by probability p One more from the midpoint 闪电从云层（顶部）劈向指针。算法很简单：连一条直线，把中点往旁边随机推一点，变成两段；再对每一段重复……It's called Middle Point Transfer 。 Per layer offset by roughness r So the broad contours bend, the detail shakes, and they form Fractal . The fork ends with a certain probability of growing a more detailed secondary route at the midpoint. Each flash generates a new shape, then a rapid index decline.