Clyune Component GalleryGrayscale · How it works & code
Convert colors to grayscale with equal brightness
Runtime logic
Visiting `/filters/grayscale`, DemoHost lazy-loads `demos/kits/kit-filters.js` (registry `mod: 'kit-filters'`) and calls `mount(host, { variant: 'grayscale' })`. mount resolves the variant to family `grayscale`; `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.grayscale (L247-L250)
Code walkthrough
L247-250: Calls the factory `colorFam()` to produce the full definition (spec + doc + build) from the options below. L247-247: Title shown in the info and control panels: “Grayscale”. L247-247: Label of the on-stage input pill. L247-247: Minimum. L247-247: Maximum. L247-247: Step. L247-247: Default value. L247-247: Default main colour. L247-247: Equivalent CSS (for reference). L248-248: Help text of the extra parameter. L249-249: Preset buttons: name → parameter overrides (5). L250-250: Body of the “Notes” section. L250-250: Main formula of the “Formula” section. L250-250: Second formula line.
Principles
Gray = 0.2126R + 0.7152G + 0.0722B Result = Original Color + a · (Gray − Original Color) Greyscale Grayscale(): replace the colour with the same grey. Eyes are the most sensitive to green, The least sensitive to blue, so green weights are the largest in the calculation of brightness (0.7152), and blue is the smallest (0.0722). a Insert values between original and grey maps. 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。