Clyune Component GalleryTOC Highlight · How it works & code
The table of contents next to long documents automatically highlights the current section as you scroll.
Runtime logic
Visiting `/scroll-fx/toc`, DemoHost lazy-loads `demos/kits/kit-scroll.js` (registry `mod: 'kit-scroll'`) and calls `mount(host, { variant: 'toc' })`. mount resolves the variant to family `toc`; `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; 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.fillRect() — Fills a rectangle; ctx.fill() — Fills the current path; ctx.fillText() — Draws filled text; ctx.beginPath() — Starts a new path; ctx.moveTo() — Moves the pen without drawing; ctx.arcTo() — Adds an arc using tangent lines; ctx.closePath() — Closes the current sub-path; ctx.stroke() — Strokes the current path; ctx.save() — Saves the drawing state (transform, styles, clip); ctx.rect() — Adds a rectangle to the path; ctx.clip() — Turns the current path into the clipping region; ctx.translate() — Translates the coordinate system; ctx.restore() — Restores the saved drawing state
Source code
frontend/src/demos/kits/kit-scroll.js: FAM.toc (L407-L421)
Code walkthrough
L407-421: Calls the factory `scFam()` to produce the full definition (spec + doc + build) from the options below. L407-407: Title shown in the info and control panels: “TOC Highlight”. L407-407: Range/default of the count slider. L407-407: Extra demo-specific slider/toggle: Capsule Highlight. L407-407: Range/default of the size slider. L407-407: Default main colour. L408-408: Help text of the count parameter. L408-408: Help text of the extra parameter. L408-408: Help text of the size parameter. L409-409: Preset buttons: name → parameter overrides (4). L410-410: Body of the “Notes” section. L411-411: Main formula of the “Formula” section. L411-411: Second formula line. L412-421: Per-frame draw function: draws with Canvas 2D `fillRect`, `fill`; math via `Math.min`, `Math.floor`, `Math.round`, `Math.max`; returns readouts `mode`, `cell`, `pageH` to the info panel.
Principles
f = (scrollY + 0.3 · High-visibility) / Chapter High Highlighted position = directory entry (f) (decimal part smooth plug) Directory Highlight: A directory next to a long document will automatically highlight the current chapter as you read it. The way to do this is to find the last chapter of the "top has crossed 30% of the viewer" and highlight it in the directory; the position of the high-lighted block is marked with a continuous decimal plug-in, so it slides smoothly down to the next item, rather than skipping. When you narrow the screen, the directory becomes a top row label. 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.