Clyune Component GalleryPinned Sections · How it works & code
Section titles follow the scroll of content normally. When a section reaches the top of the viewport, it sticks there. The title remains in place until the entire section has scrolled past, then it is pushed away by the next section.
Runtime logic
Visiting `/scroll-fx/pin`, DemoHost lazy-loads `demos/kits/kit-scroll.js` (registry `mod: 'kit-scroll'`) and calls `mount(host, { variant: 'pin' })`. mount resolves the variant to family `pin`; `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.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.fillRect() — Fills a rectangle; 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.pin (L210-L226)
Code walkthrough
L210-226: Calls the factory `scFam()` to produce the full definition (spec + doc + build) from the options below. L210-210: Title shown in the info and control panels: “Pinned Sections”. L210-210: Range/default of the count slider. L210-210: Extra demo-specific slider/toggle: Pinned Duration. L210-210: Range/default of the size slider. L210-210: Default main colour. L211-211: Help text of the count parameter. L211-211: Help text of the extra parameter. L211-211: Help text of the size parameter. L212-212: Preset buttons: name → parameter overrides (5). L213-213: Body of the “Notes” section. L214-214: Main formula of the “Formula” section. L214-214: Second formula line. L215-226: Per-frame draw function: draws with Canvas 2D `fill`; math via `Math.min`, `Math.max`; returns readouts `mode`, `cell`, `pageH` to the info panel.
Principles
Title y = min (max (top of chapter - scrollY, 0), bottom of chapter - scrollY - top of title) Chapter High = Visual High · (1 + pin duration) Chapter pinned down (position: sticky): The title of the chapter is normally rolled along with the contents, and once it touches the top of the view, it is " sticky" at the top; the title is not pushed away until the contents of this chapter have been rolled out. Sticky is restricted to its parent element (this chapter). 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.