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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';
import "hammerjs";
/**
* Mousewheel and pinch zoom handler.
*/
export default class LdZoom {
readonly containerElement: HTMLDivElement;
readonly imageElement: HTMLImageElement;
readonly maxScaleFactor: number;
readonly scrollZoomSpeed: number;
scaleFactor: number = 0.0;
constructor(
containerElement: HTMLDivElement, imageElement: HTMLImageElement,
maxScaleFactor: number, scrollZoomSpeed: number
) {
this.containerElement = containerElement;
this.imageElement = imageElement;
this.maxScaleFactor = maxScaleFactor;
this.scrollZoomSpeed = scrollZoomSpeed;
}
/**
* 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();
const zoomDelta = -Math.sign(wheelEvent.deltaY) * this.scrollZoomSpeed;
this.zoom(wheelEvent.offsetX, wheelEvent.offsetY, zoomDelta);
});
const pinchListener = new Hammer(this.containerElement);
pinchListener.get('pinch').set({enable: true});
this.installPinchHandler(pinchListener);
}
private installPinchHandler(pinchListener: HammerManager) {
let lastScaleFactor = 0.0;
pinchListener.on('pinchstart', (pinchEvent: HammerInput) => {
lastScaleFactor = pinchEvent.scale;
});
pinchListener.on('pinchmove', (pinchEvent: HammerInput) => {
// FIXME: pinchEvent.center isn't always well-centered
const focusX = pinchEvent.center.x + this.containerElement.scrollLeft;
const focusY = pinchEvent.center.y + this.containerElement.scrollTop;
const zoomDelta = pinchEvent.scale - lastScaleFactor;
lastScaleFactor = pinchEvent.scale;
this.zoom(focusX, focusY, zoomDelta);
});
}
/**
* 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(focusX: number, focusY: number, zoomDelta: number) {
const ratioX = focusX / this.imageElement.clientWidth;
const ratioY = focusY / this.imageElement.clientHeight;
this.setImageScale(Math.min(this.scaleFactor + zoomDelta, this.maxScaleFactor));
this.containerElement.scrollLeft -= focusX - ratioX * this.imageElement.clientWidth;
this.containerElement.scrollTop -= focusY - 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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