Clyune Component GallerySticky · How it works & code
position:sticky for sidebar/section
Runtime logic
Visiting `/layout/sticky`, DemoHost lazy-loads `demos/kits/kit-layout.js` (registry `mod: 'kit-layout'`) and calls `mount(host, { variant: 'sticky' })`. mount resolves the variant to family `sticky`; `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.save() — Saves the drawing state (transform, styles, clip); ctx.beginPath() — Starts a new path; ctx.rect() — Adds a rectangle to the path; ctx.clip() — Turns the current path into the clipping region; ctx.fill() — Fills the current path; ctx.restore() — Restores the saved drawing state; ctx.fillText() — Draws filled text; ctx.moveTo() — Moves the pen without drawing; ctx.arcTo() — Adds an arc using tangent lines; ctx.closePath() — Closes the current sub-path; ctx.measureText() — Measures text width; ctx.stroke() — Strokes the current path
Source code
frontend/src/demos/kits/kit-layout.js: FAM.sticky (L289-L337), TITLES['sticky'] (L647-L647)
Code walkthrough
L291-291: Control definitions (colour/speed/size/count/extras): Sticky Bar Color, Sidebar Width, Number of Sections, sticky top, Top Bar Also Sticky. L292-292: Preset buttons: name → parameter overrides (6). L293-301: Info-panel content: live rows(v), formula, notes, params, steps. L302-336: Init function: sets up state and returns the per-frame callback: draws with Canvas 2D `save`, `beginPath`, `rect`, `clip`, `fill`, `restore`; math via `Math.round`, `Math.max`, `Math.sin`, `Math.min`; returns readouts `scroll`, `top`, `sw`, `cell`, `stuck`, `n` to the info panel. L647-647: This demo's entry in the `TITLES` table (title).
Principles
position: sticky; top: T Element scrolls in the normal document stream until the top of the view ≤ T, And then it's stuck Sticky failure when parent spills or no remaining space sticky 介于相对与固定之间：平常跟着页面滚，滚到阈值（如 top:8px）就吸在那儿，直到父容器底边把它带走。侧栏目录、表头常用。 This presentation simulates a scroll in the canvas. Sidebar is arriving top; the right chapter list continues to roll. Speed>0.