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/* ldgallery - A static generator which turns a collection of tagged
-- pictures into a searchable web gallery.
--
-- Copyright (C) 2020 Pacien TRAN-GIRARD
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU Affero General Public License as
-- published by the Free Software Foundation, either version 3 of the
-- License, or (at your option) any later version.
--
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-- GNU Affero General Public License for more details.
--
-- You should have received a copy of the GNU Affero General Public License
-- along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
// polyfill still required for IE and Safari, see https://caniuse.com/#feat=resizeobserver
import ResizeObserver from 'resize-observer-polyfill';
/**
* Mousewheel picture zoom helper.
*/
export default class LdZoom {
readonly containerElement: HTMLDivElement;
readonly imageElement: HTMLImageElement;
readonly maxScaleFactor: number;
readonly zoomSpeed: number;
scaleFactor: number = 0.0;
constructor(
containerElement: HTMLDivElement, imageElement: HTMLImageElement,
maxScaleFactor: number, zoomSpeed: number
) {
this.containerElement = containerElement;
this.imageElement = imageElement;
this.maxScaleFactor = maxScaleFactor;
this.zoomSpeed = zoomSpeed;
}
/**
* Register event listeners.
* The dimension of the image should be known before calling this method.
*/
public install() {
new ResizeObserver(() => {
this.setImageScale(this.scaleFactor);
this.recenterImageElement();
}).observe(this.containerElement);
this.containerElement.addEventListener('wheel', wheelEvent => {
wheelEvent.preventDefault();
this.zoom(wheelEvent);
});
// TODO: handle pinch-to-zoom.
}
/**
* Centers the image element inside its container if it fits, or stick to the top and left borders otherwise.
* It's depressingly hard to do in pure CSS…
*/
private recenterImageElement() {
const marginLeft = Math.max((this.containerElement.clientWidth - this.imageElement.clientWidth) / 2, 0);
const marginTop = Math.max((this.containerElement.clientHeight - this.imageElement.clientHeight) / 2, 0);
this.imageElement.style.marginLeft = `${marginLeft}px`;
this.imageElement.style.marginTop = `${marginTop}px`;
}
private zoom(wheelEvent: WheelEvent) {
const ratioX = wheelEvent.offsetX / this.imageElement.clientWidth;
const ratioY = wheelEvent.offsetY / this.imageElement.clientHeight;
const zoomDelta = -Math.sign(wheelEvent.deltaY) * this.zoomSpeed;
this.setImageScale(Math.min(this.scaleFactor + zoomDelta, this.maxScaleFactor));
this.containerElement.scrollLeft -= wheelEvent.offsetX - ratioX * this.imageElement.clientWidth;
this.containerElement.scrollTop -= wheelEvent.offsetY - ratioY * this.imageElement.clientHeight;
}
private setImageScale(newScaleFactor: number) {
const horizontalFillRatio = this.containerElement.clientWidth / this.imageElement.naturalWidth;
const verticalFillRatio = this.containerElement.clientHeight / this.imageElement.naturalHeight;
const minScaleFactor = Math.min(horizontalFillRatio, verticalFillRatio, 1.0);
this.scaleFactor = Math.max(newScaleFactor, minScaleFactor);
this.imageElement.width = this.scaleFactor * this.imageElement.naturalWidth;
this.imageElement.height = this.scaleFactor * this.imageElement.naturalHeight;
this.recenterImageElement();
}
}
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