Clyune Component GalleryScroll Path Drawing · How it works & code
A serpentine SVG path spans across the entire page.
Runtime logic
Visiting `/scroll-fx/path-draw`, DemoHost lazy-loads `demos/kits/kit-scroll.js` (registry `mod: 'kit-scroll'`) and calls `mount(host, { variant: 'path-draw' })`. mount resolves the variant to family `path-draw`; `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°); TAU — Constant 2π; fmt — Number formatting (fixed decimals); F — Formula block HTML; S.clear — Clears with the background colour (translucent = trails); S.isAutoDemo — Whether auto demo is on; S.onFrame — Registers a per-frame callback; its return value feeds the info panel; ctx.save() — Saves the drawing state (transform, styles, clip); ctx.translate() — Translates the coordinate system; ctx.stroke() — Strokes the current path; ctx.beginPath() — Starts a new path; ctx.arc() — Adds a circular arc (center, radius, start/end angle); ctx.fill() — Fills the current path; ctx.restore() — Restores the saved drawing state; ctx.moveTo() — Moves the pen without drawing; ctx.arcTo() — Adds an arc using tangent lines; ctx.closePath() — Closes the current sub-path; ctx.setLineDash() — Sets the dash pattern for strokes; 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-scroll.js: FAM.path-draw (L316-L334)
Code walkthrough
L316-334: Calls the factory `scFam()` to produce the full definition (spec + doc + build) from the options below. L316-316: Title shown in the info and control panels: “Scroll Path Drawing”. L316-316: Range/default of the count slider. L316-316: Extra demo-specific slider/toggle: Glow. L316-316: Range/default of the size slider. L316-316: Default main colour. L317-317: Help text of the count parameter. L317-317: Help text of the extra parameter. L317-317: Help text of the size parameter. L318-318: Preset buttons: name → parameter overrides (4). L319-319: Body of the “Notes” section. L320-320: Main formula of the “Formula” section. L320-320: Second formula line. L321-334: Per-frame draw function: draws with Canvas 2D `save`, `translate`, `stroke`, `beginPath`, `arc`, `fill` …; math via `Math.hypot`, `Math.round`; returns readouts `mode`, `cell`, `pageH` to the info panel.
Principles
Target Line = scrollY + 0.6 · Eyes high Visible length = length of path above target line Path rolling: A snake-shaped SVG path runs through the entire page. When you scroll, the calculation page is located at 60% of the height of the viewer, drawing the path from the starting point to the line (stroke-dashoffset), just as the line follows the reader down the line; the passing nodes are lit. Image simulates a scrollable web page: scrollY 表示页面已经向上滚过了多少像素，这里它自动来回滚动（右侧细条就是滚动条）。元素在屏幕上的位置 = Page Location − scrollY；The degree to which the elements enter the vision is usually used scroll Event or event IntersectionObserver Let's figure this out 0~1 The progress is driven by animations such as transparency, offset, scaling, etc.