Clyune Component GalleryPointer Trail · How it works & code
Chain interpolation pointer trail ribbon.
Runtime logic
Visiting `/canvas/trail`, DemoHost lazy-loads `demos/kits/kit-canvas.js` (registry `mod: 'kit-canvas'`) and calls `mount(host, { variant: 'trail' })`. mount resolves the variant to family `trail`; `withControls` builds the control panel (10 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. 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; rgba — Builds an rgba() colour string; hueOf — Hue of a colour (0–360°); clamp — Clamps a value to a range; TAU — Constant 2π; fmt — Number formatting (fixed decimals); F — Formula block HTML; 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.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.createRadialGradient() — Creates a radial gradient; 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.trail (L275-L311)
Code walkthrough
L277-277: Control definitions (colour/speed/size/count/extras): Trail Color, Trail Thickness, Node Count n, Follow Coefficient k, Rainbow Gradient. L278-278: Preset buttons: name → parameter overrides (10). L279-287: Info-panel content: live rows(v), formula, notes, params, steps. L288-310: Init function: sets up state and returns the per-frame callback: draws with Canvas 2D `beginPath`, `moveTo`, `lineTo`, `stroke`, `createRadialGradient`, `arc` …; math via `Math.round`, `Math.pow`, `Math.max`, `Math.log`, `Math.hypot`; returns readouts `n`, `k`, `half`, `vh`, `lag`, `rb` to the info panel.
Principles
Each frame: pᵢ ← pᵢ + k·(pᵢ₋₁ − pᵢ), p₀ Follow Pointer Left gap per frame ×(1 − k)，Half-life = ln 0.5 / ln(1 − k) 帧 Line width wᵢ = 12 × Thickness × (1 − i / n) Drag End by n Composition of nodes. I don't think so 0 A pointer, no 1 That's the best 0 ……Each node only walks through the remaining distance k Double, that's it Linear Plugin (Line Plugin) lerp) 。 Because every section is“Slow down”, The whole line is like a towed ribbon. k (b) It's not a good idea k The bigger the pointer, the closer. Threads become thinner from the beginning to the end, forming the hidden tail.