Staggered Cards · How it works & code
Staggered entry: a group of cards performs the same animation, but each card starts slightly later than the previous one (stagger gap).
Runtime logic
Visiting `/gsap/stagger`, DemoHost lazy-loads `demos/kits/kit-gsap.js` (registry `mod: 'kit-gsap'`) and calls `mount(host, { variant: 'stagger' })`. mount resolves the variant to family `stagger`; `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; 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.setLineDash() — Sets the dash pattern for strokes; ctx.stroke() — Strokes the current path; 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.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-gsap.js: FAM.stagger (L273-L287)
Code walkthrough
L273-287: Calls the factory `gFam()` to produce the full definition (spec + doc + build) from the options below. L273-273: Title shown in the info and control panels: “Staggered Cards”. L273-273: Range/default of the count slider. L273-273: Extra demo-specific slider/toggle: Stagger gap. L273-273: Range/default of the size slider. L273-273: Default main colour. L274-274: Help text of the count parameter. L274-274: Help text of the extra parameter. L274-274: Help text of the size parameter. L275-275: Preset buttons: name → parameter overrides (5). L276-276: Body of the “Notes” section. L277-277: Main formula of the “Formula” section. L277-277: Second formula line. L278-287: Per-frame draw function: draws with Canvas 2D `setLineDash`, `stroke`, `fill`; math via `Math.round`; returns readouts `mode`, `cell` to the info panel.
Principles
第 i Delay of a card = i · each,ease: power2.out gsap.from(".card", { y: 30, opacity: 0, duration: 0.6, stagger: { each: 0.08 } }) stagger 交错:给一组元素同一个动画,但让它们依次出发。每张卡片上的数字就是它的延迟时间(第几张 × 间隔)。卡片先从下方淡入,停一会儿,再按同样的顺序向上淡出。虚线框是卡片最终停放的位置。 There's no load here GSAP 库,而是用几十行代码复刻了它最核心的几个概念:补间(tween,从 A Smooth transition of value B Value, slow motion ease,Control the slow pace of transition, the time axis timeline,Sort multi-part patches in order) and staggered ( stagger,让一组元素依次出发)。每一帧都直接根据「当前时间」算出画面,所以拖动右侧滑条会立即看到变化。公式区给出了对应的 GSAP In writing, you can move directly to the real project.