Clyune Component GalleryPath Following · How it works & code
Objects move along the path.
Runtime logic
Visiting `/svg/follow`, DemoHost lazy-loads `demos/kits/kit-svg.js` (registry `mod: 'kit-svg'`) and calls `mount(host, { variant: 'follow' })`. mount resolves the variant to family `follow`; `withControls` builds the control panel (6 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; hueOf — Hue of a colour (0–360°); clamp — Clamps a value to a range; fmt — Number formatting (fixed decimals); F — Formula block HTML; S.clear — Clears with the background colour (translucent = trails); S.onFrame — Registers a per-frame callback; its return value feeds the info panel; ctx.setLineDash() — Sets the dash pattern for strokes; ctx.stroke() — Strokes the current path; ctx.save() — Saves the drawing state (transform, styles, clip); ctx.translate() — Translates the coordinate system; ctx.rotate() — Rotates the coordinate system; ctx.beginPath() — Starts a new path; ctx.moveTo() — Moves the pen without drawing; ctx.lineTo() — Adds a straight line to a point; ctx.closePath() — Closes the current sub-path; ctx.fill() — Fills the current path; ctx.restore() — Restores the saved drawing state; ctx.arcTo() — Adds an arc using tangent lines; ctx.fillRect() — Fills a rectangle; ctx.rect() — Adds a rectangle to the path; ctx.clip() — Turns the current path into the clipping region
Source code
frontend/src/demos/kits/kit-svg.js: FAM.follow (L437-L451)
Code walkthrough
L437-451: Calls the factory `sFam()` to produce the full definition (spec + doc + build) from the options below. L437-437: Title shown in the info and control panels: “Path Following”. L437-437: Range/default of the count slider. L437-437: Extra demo-specific slider/toggle: Spacing. L437-437: Range/default of the size slider. L437-437: Default main colour. L438-438: Help text of the count parameter. L438-438: Help text of the extra parameter. L438-438: Help text of the size parameter. L439-439: Preset buttons: name → parameter overrides (5). L440-440: Body of the “Notes” section. L441-441: Main formula of the “Formula” section. L441-441: Second formula line. L442-451: Per-frame draw function: draws with Canvas 2D `setLineDash`, `stroke`, `save`, `translate`, `rotate`, `beginPath` …; math via `Math.min`, `Math.hypot`, `Math.round`; returns readouts `mode`, `cell` to the info panel.
Principles
Positioni = getPointAtLength · fract(0.12t − i · ) = atan2(dy, dx) (tangular direction) Path follows: 让元素沿着路径移动，并按路径的切线方向自动转向。原理是用 getPointAtLength(Progress · L) 取路径上的点，再用前后两点算出切线角度。多个物体用同一条路径、错开固定的「间隔」，就排成了一列队伍。 SVG It's "The Vector Chart in Text":<path d="M… L… C… A…"> 里 M Means moving to a point, L Draw straight lines, C Draw three Bézier curves, A Draw round a Elimination Translate. Here Canvas 的 Path2D Parsing the same path, then pressing time t 改变描边、形状、颜色等属性，效果与网页里的 SVG Animated same.