Clyune Component GalleryBackground Shift · How it works & code
The page is divided into segments, each with a specified background color.
Runtime logic
Visiting `/scroll-fx/bg-shift`, DemoHost lazy-loads `demos/kits/kit-scroll.js` (registry `mod: 'kit-scroll'`) and calls `mount(host, { variant: 'bg-shift' })`. mount resolves the variant to family `bg-shift`; `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.beginPath() — Starts a new path; ctx.arc() — Adds a circular arc (center, radius, start/end angle); ctx.fill() — Fills the current path; 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.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
Source code
frontend/src/demos/kits/kit-scroll.js: FAM.bg-shift (L356-L370)
Code walkthrough
L356-370: Calls the factory `scFam()` to produce the full definition (spec + doc + build) from the options below. L356-356: Title shown in the info and control panels: “Background Shift”. L356-356: Range/default of the count slider. L356-356: Extra demo-specific slider/toggle: Transition Width. L356-356: Range/default of the size slider. L356-356: Default main colour. L357-357: Help text of the count parameter. L357-357: Help text of the extra parameter. L357-357: Help text of the size parameter. L358-358: Preset buttons: name → parameter overrides (5). L359-359: Body of the “Notes” section. L360-360: Main formula of the “Formula” section. L360-360: Second formula line. L361-370: Per-frame draw function: draws with Canvas 2D `fillRect`, `beginPath`, `arc`, `fill`; math via `Math.min`, `Math.floor`, `Math.round`; returns readouts `mode`, `cell`, `pageH` to the info panel.
Principles
f = scrollY / Height, m = slow motion ((f-⌊f-0.5) / Transitional width +0.5 Background = color (⌊f⌋)+ (⌊f⌋+1) - color (⌊f⌋) m Background colour change: The page is Extensi EDUCATIONally divided into several 1-3 paragraphs ICPD and each Concerted paragraph specifies a background colour. Arabian resubmits Target The smaller the length of the transition Extensi EDUCATION, the longer the 1-3- ICPD Colour Stay Concerted, Switch faster. 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.