Clyune Component GalleryContrast · How it works & code
The distance from each channel to the centre is multiplied by a multiple, with middle ash (0.5).
Runtime logic
Visiting `/filters/contrast`, DemoHost lazy-loads `demos/kits/kit-filters.js` (registry `mod: 'kit-filters'`) and calls `mount(host, { variant: 'contrast' })`. mount resolves the variant to family `contrast`; `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.onFrame — Registers a per-frame callback; its return value feeds the info panel; 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.fill() — Fills the current path; ctx.stroke() — Strokes the current path; ctx.createLinearGradient() — Creates a linear gradient; ctx.fillRect() — Fills a rectangle; ctx.arc() — Adds a circular arc (center, radius, start/end angle); ctx.lineTo() — Adds a straight line to a point; ctx.save() — Saves the drawing state (transform, styles, clip); ctx.clip() — Turns the current path into the clipping region; ctx.drawImage() — Draws an image or offscreen canvas
Source code
frontend/src/demos/kits/kit-filters.js: FAM.contrast (L231-L234)
Code walkthrough
L231-234: Calls the factory `colorFam()` to produce the full definition (spec + doc + build) from the options below. L231-231: Title shown in the info and control panels: “Contrast”. L231-231: Label of the on-stage input pill. L231-231: Minimum. L231-231: Maximum. L231-231: Step. L231-231: Default value. L231-231: Default main colour. L231-231: Equivalent CSS (for reference). L232-232: Help text of the extra parameter. L233-233: Preset buttons: name → parameter overrides (5). L234-234: Body of the “Notes” section. L234-234: Main formula of the “Formula” section. L234-234: Second formula line.
Principles
v → (v − 0.5) · a + 0.5 The channel value of v is 0...1 Contrast(): with middle ash (0.5), multiply the distance from each channel to the centre by a multiple. A multiple greater than 1 lighter, It's darker, it's hard; it's less than 1 when all the colors converge to grey, it's gray. 为了在所有浏览器里效果一致，这里没有直接调用 CSS 的 filter，而是把一张会动的风景「照片」先画到一块小画布上，再按 W3C 规范里每个滤镜的公式逐个像素计算颜色，最后放大显示。中间那条竖线左边是原图、右边是滤镜后的结果，竖线会跟着指针移动；把指针放在图上，信息面板会显示这一点滤镜前后的颜色。