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49 lines
1.8 KiB
49 lines
1.8 KiB
import {dom, IDomArgs, Observable, styled} from 'grainjs';
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// Shadow css settings for member scroll top and bottom.
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const SHADOW_TOP = 'inset 0 4px 6px 0 var(--grist-theme-scroll-shadow, rgba(217,217,217,0.4))';
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const SHADOW_BTM = 'inset 0 -4px 6px 0 var(--grist-theme-scroll-shadow, rgba(217,217,217,0.4))';
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/**
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* Creates a scroll div used in the UserManager and moveDoc menus to display
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* shadows at the top and bottom of a list of scrollable items.
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*/
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export function shadowScroll(...args: IDomArgs<HTMLDivElement>) {
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// Observables to indicate the scroll position.
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const scrollTop = Observable.create(null, true);
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const scrollBtm = Observable.create(null, true);
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return cssScrollMenu(
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dom.autoDispose(scrollTop),
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dom.autoDispose(scrollBtm),
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// Update scroll positions on init and on scroll.
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(elem) => { setTimeout(() => scrollBtm.set(isAtScrollBtm(elem)), 0); },
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dom.on('scroll', (_, elem) => {
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scrollTop.set(isAtScrollTop(elem));
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scrollBtm.set(isAtScrollBtm(elem));
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}),
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// Add shadows on the top/bottom if the list is scrolled away from either.
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dom.style('box-shadow', (use) => {
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const shadows = [use(scrollTop) ? null : SHADOW_TOP, use(scrollBtm) ? null : SHADOW_BTM];
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return shadows.filter(css => css).join(', ');
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}),
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...args
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);
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}
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// Indicates that an element is currently scrolled such that the top of the element is visible.
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function isAtScrollTop(elem: Element): boolean {
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return elem.scrollTop === 0;
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}
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// Indicates that an element is currently scrolled such that the bottom of the element is visible.
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// It is expected that the elem arg has the offsetHeight property set.
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function isAtScrollBtm(elem: HTMLElement): boolean {
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return elem.scrollTop >= (elem.scrollHeight - elem.offsetHeight);
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}
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const cssScrollMenu = styled('div', `
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flex: 1 1 0;
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width: 100%;
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overflow-y: auto;
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`);
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