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diff --git a/viewer/src/services/ui/ldZoom.ts b/viewer/src/services/ui/ldZoom.ts
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+++ b/viewer/src/services/ui/ldZoom.ts
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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/>.
+*/
+
+import { PictureProperties, Resolution } from '@/@types/gallery';
+import { importHammer } from '@/plugins/asyncLib';
+import { CSSProperties, Ref } from 'vue';
+
+/**
+ * Mousewheel and pinch zoom handler.
+ */
+export const useLdZoom = (
+  imageStyle: Ref<CSSProperties>,
+  containerElement: HTMLDivElement,
+  imageElement: HTMLImageElement,
+  pictureProperties: PictureProperties,
+  maxScaleFactor = 10,
+  scrollZoomSpeed: number = 1 / 7,
+) => {
+  let scaleFactor = 0.0;
+
+  /**
+   * Register event listeners.
+   */
+  updateImageScale(scaleFactor);
+
+  new ResizeObserver(() => {
+    updateImageScale(scaleFactor);
+  }).observe(containerElement);
+
+  containerElement.addEventListener('wheel', wheelEvent => {
+    wheelEvent.preventDefault();
+    const newScaleFactor = scaleFactor - Math.sign(wheelEvent.deltaY) * (scrollZoomSpeed * scaleFactor);
+    zoom(wheelEvent.offsetX, wheelEvent.offsetY, newScaleFactor);
+  });
+
+  importHammer().then(() => {
+    const pinchListener = new Hammer(containerElement);
+    pinchListener.get('pinch').set({ enable: true });
+    installPinchHandler(pinchListener);
+  });
+
+  return { imageStyle };
+
+  // ---
+
+  function installPinchHandler(pinchListener: HammerManager) {
+    let startScaleFactor = 0.0;
+
+    pinchListener.on('pinchstart', () => {
+      startScaleFactor = scaleFactor;
+    });
+
+    pinchListener.on('pinchmove', (pinchEvent: HammerInput) => {
+      const focusX = pinchEvent.center.x + containerElement.scrollLeft;
+      const focusY = pinchEvent.center.y + containerElement.scrollTop;
+      const scaleFactor = pinchEvent.scale * startScaleFactor;
+      zoom(focusX, focusY, scaleFactor);
+    });
+  }
+
+  /**
+   * Returns the picture resolution as it should be displayed.
+   */
+  function getDisplayResolution(): Resolution {
+    return {
+      width: pictureProperties.resolution.width * scaleFactor,
+      height: pictureProperties.resolution.height * scaleFactor,
+    };
+  }
+
+  /**
+   * Applies scaling to the DOM image element.
+   * To call after internal intermediate computations because DOM properties aren't stable.
+   */
+  function resizeImageElement() {
+    const imageDim = getDisplayResolution();
+    imageElement.width = imageDim.width;
+    imageElement.height = imageDim.height;
+  }
+
+  /**
+   * 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…
+   */
+  function recenterImageElement() {
+    const imageDim = getDisplayResolution();
+    const marginLeft = Math.max((containerElement.clientWidth - imageDim.width) / 2, 0);
+    const marginTop = Math.max((containerElement.clientHeight - imageDim.height) / 2, 0);
+    imageStyle.value.marginLeft = `${marginLeft}px`;
+    imageStyle.value.marginTop = `${marginTop}px`;
+  }
+
+  function zoom(focusX: number, focusY: number, scaleFactor: number) {
+    const imageDim = getDisplayResolution();
+    const ratioX = focusX / imageDim.width;
+    const ratioY = focusY / imageDim.height;
+    updateImageScale(Math.min(scaleFactor, maxScaleFactor));
+
+    const newImageDim = getDisplayResolution();
+    containerElement.scrollLeft -= focusX - ratioX * newImageDim.width;
+    containerElement.scrollTop -= focusY - ratioY * newImageDim.height;
+  }
+
+  function updateImageScale(newScaleFactor: number) {
+    const horizontalFillRatio = containerElement.clientWidth / pictureProperties.resolution.width;
+    const verticalFillRatio = containerElement.clientHeight / pictureProperties.resolution.height;
+    const minScaleFactor = Math.min(horizontalFillRatio, verticalFillRatio, 1.0);
+    scaleFactor = Math.max(newScaleFactor, minScaleFactor);
+    resizeImageElement();
+    recenterImageElement();
+  }
+};