Stack cover

When to use

Use when the next shot is a new panel that should feel like a sheet laid over the last one. The sheet slides in from the side; the old shot moves a quarter as far, shrinks a little and dims, so the two sit at different depths. The detail that sells it is the shadow: it is cast by the sheet's leading edge and grows wider and darker as the overlap grows. Clip: stack-cover.mp4. Demo: demo/stack-cover.html.

The code

import { EASE, easeFn } from '../../core/motion/presets.js';
const W = innerWidth;
const opt = { duration: 1000, delay: 200, easing: EASE.land, fill: 'both' };
sheet.animate([{ translate: `${W}px 0` }, { translate: '0 0' }], opt);
old.animate([{ translate: '0 0', scale: 1 }, { translate: `${-W * 0.24}px 0`, scale: 0.96 }], opt);
dim.animate([{ opacity: 0 }, { opacity: 0.4 }], opt);                       // #14103a over the old shot
cast.animate([{ opacity: 0.25, scale: '0.35 1' }, { opacity: 1, scale: '1 1' }], opt);   // right:100% of the sheet, transform-origin: right
copy.animate([{ translate: '9vw 0' }, { translate: '0 0' }], { ...opt, duration: 1100 }); // lags the sheet
// blur only the sheet body (not the cast): stdDeviation = 0.25 x one frame's travel, x only, set in vawe.onFrame as in push-blur

Easing and timing

The clip runs 1.6 s. The look is chrome.

The clip uses one named ease from core/motion/presets.js. Each is a pair of After Effects handles: influence is how far along the segment the handle reaches, and speed is how fast the value moves at the key, as a multiple of the segment's average speed. Motion in the docs explains both.

Notes

The cast is a 34 vw wide gradient that falls off in 5 stops (0.34 to 0 alpha), not a box-shadow: a box-shadow cannot grow with progress. Keep it outside the blurred element or the blur turns it to bands. Make the sheet 4.4 percent wider than the frame and start it that far left, so its rounded leading corners are off screen once it lands. The old shot must move about a quarter as far: equal speeds read as a slide, not a stack. Let the copy lag the sheet by 9 vw so the sheet is a surface with things on it.

Looks (ground, type, radius, accent) live in demo/demo.css; this snippet keeps neutral tokens.

Sound

Sound: none; a soft cut stays soft.