viewer/LdPicture: implement mousewheel zoom

GitHub: closes #153

2 files changed, 123 insertions, 30 deletions

diff --git a/viewer/src/components/LdPicture.vue b/viewer/src/components/LdPicture.vue
index 3170c81..622165d 100644
--- a/viewer/src/components/LdPicture.vue
+++ b/viewer/src/components/LdPicture.vue
@@ -19,31 +19,37 @@
 
 <template>
   <div
+    ref="containerElement"
     v-dragscroll
-    class="scrollbar"
-    :class="{'fit-to-screen': !$uiStore.fullscreen, 'original-size': $uiStore.fullscreen}"
+    class="scrollbar ld-picture-container"
     @click.capture="e => dragScrollClickFix.onClickCapture(e)"
-    @click="$uiStore.toggleFullscreen()"
+    @dblclick="$uiStore.toggleFullscreen()"
+    @dragstart.prevent
     @dragscrollstart="dragScrollClickFix.onDragScrollStart()"
     @dragscrollend="dragScrollClickFix.onDragScrollEnd()"
   >
     <v-lazy-image
+      ref="imageElement"
       :src="pictureSrc(picture.properties.resource)"
+      class="ld-picture-element"
       :class="{'slow-loading': Boolean(slowLoadingStyle)}"
       :style="slowLoadingStyle"
-      @load="clearSlowLoading"
+      @load="lazyImageLoaded"
     />
     <b-loading :active="loader" :is-full-page="false" class="ld-picture-loader" />
   </div>
 </template>
 
 <script lang="ts">
-import { Component, Vue, Prop } from "vue-property-decorator";
+import { Component, Vue, Prop, Ref } from "vue-property-decorator";
+import LdZoom from "@/services/ldzoom";
 import DragScrollClickFix from "@/services/dragscrollclickfix";
 
 @Component
 export default class LdPicture extends Vue {
   @Prop({ required: true }) readonly picture!: Gallery.Picture;
+  @Ref() readonly containerElement!: HTMLDivElement;
+  @Ref() readonly imageElement!: any; // FIXME: no typedef for v-lazy-image
 
   readonly SLOW_LOADING_TIMEOUT_MS: number = 1500;
   readonly dragScrollClickFix = new DragScrollClickFix();
@@ -60,6 +66,11 @@ export default class LdPicture extends Vue {
     this.clearSlowLoading();
   }
 
+  lazyImageLoaded() {
+    this.clearSlowLoading();
+    new LdZoom(this.containerElement, this.imageElement.$el, 10, 1 / 5).install();
+  }
+
   clearSlowLoading() {
     if (this.timer) clearTimeout(this.timer);
     this.timer = null;
@@ -85,13 +96,17 @@ export default class LdPicture extends Vue {
 <style lang="scss">
 @import "~@/assets/scss/theme.scss";
 
-.ld-picture-loader {
-  position: relative;
-  & .loading-background {
-    background: none !important;
-  }
+.ld-picture-container {
+  height: 100%;
+}
+
+.ld-picture-element {
+  max-width: unset;
+  max-height: unset;
+  cursor: grab;
 }
-img.slow-loading {
+
+.slow-loading {
   background-repeat: no-repeat;
   background-position: center;
   background-size: contain;
@@ -99,25 +114,11 @@ img.slow-loading {
   background-blend-mode: soft-light;
   opacity: 1 !important;
 }
-.fit-to-screen {
-  display: flex;
-  justify-content: space-around;
-  height: 100%;
-  & > img {
-    object-fit: contain;
-    cursor: zoom-in;
-  }
-}
-.original-size {
-  display: block;
-  text-align: center;
-  cursor: grab;
-  height: 100%;
-  & > img {
-    max-width: unset;
-    max-height: unset;
-    object-fit: none;
-    cursor: zoom-out;
+
+.ld-picture-loader {
+  position: relative;
+  & .loading-background {
+    background: none !important;
   }
 }
 </style>
diff --git a/viewer/src/services/ldzoom.ts b/viewer/src/services/ldzoom.ts
new file mode 100644
index 0000000..f001805
--- /dev/null
+++ b/viewer/src/services/ldzoom.ts
@@ -0,0 +1,92 @@
+/* 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;
+
+  constructor(
+    containerElement: HTMLDivElement, imageElement: HTMLImageElement,
+    maxScaleFactor: number, zoomSpeed: number
+  ) {
+    this.containerElement = containerElement;
+    this.imageElement = imageElement;
+    this.maxScaleFactor = maxScaleFactor;
+    this.zoomSpeed = zoomSpeed;
+    this.scaleFactor = imageElement.clientWidth / imageElement.naturalWidth;
+  }
+
+  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.
+
+    this.recenterImageElement();
+  }
+
+  /**
+   * 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();
+  }
+}