Clyune Component GalleryDropdown · How it works & code
Dropdown/Select。
Runtime logic
Visiting `/ui/drop`, DemoHost lazy-loads `demos/kits/kit-ui.js` (registry `mod: 'kit-ui'`) and calls `mount(host, { variant: 'drop' })`. mount resolves the variant to family `drop`; `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; 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.stroke() — Strokes the current path; ctx.save() — Saves the drawing state (transform, styles, clip); ctx.translate() — Translates the coordinate system; ctx.scale() — Scales the coordinate system; ctx.restore() — Restores the saved drawing state; 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.fillRect() — Fills a rectangle
Source code
frontend/src/demos/kits/kit-ui.js: FAM.drop (L267-L284)
Code walkthrough
L267-284: Calls the factory `uiFam()` to produce the full definition (spec + doc + build) from the options below. L267-267: Title shown in the info and control panels: “Dropdown”. L267-267: Range/default of the size slider: Option Height. L267-267: Range/default of the count slider: Option Count. L268-268: List of extra controls: With Search. L268-268: Preset buttons: name → parameter overrides (4). L269-269: Body of the “Notes” section. L269-269: Main formula of the “Formula” section. L269-269: Second formula line. L270-284: Per-frame draw function: draws with Canvas 2D `fill`, `stroke`, `save`, `translate`, `scale`, `restore`; math via `Math.min`, `Math.floor`; returns readouts `mode`, `cell` to the info panel.
Principles
menu: scaleY(0.9→1) + opacity Highlight row = pointer line Drop-down selection: Click the post-menu to expand from below the trigger (scaling + faded), suspend the high item and tick the current value.