viewer/LdZoom: add support for pinch-to-zoom

GitHub: closes #106

5 files changed, 46 insertions, 14 deletions

diff --git a/readme.md b/readme.md
index c3b8cb8..dc370a2 100644
--- a/readme.md
+++ b/readme.md
@@ -55,6 +55,7 @@ Builds of this software embed and make use of the following libraries:
   * buefy, licensed under the MIT License
   * core-js, licensed under the MIT License
   * resize-observer-polyfill, licensed under the MIT License
+  * hammerjs, licensed under the MIT License
   * v-lazy-image, licensed under the MIT License
   * vue, licensed under the MIT License
   * vue-class-component, licensed under the MIT License
diff --git a/viewer/package-lock.json b/viewer/package-lock.json
index 1e1fdda..d4a5fb0 100644
--- a/viewer/package-lock.json
+++ b/viewer/package-lock.json
@@ -1232,6 +1232,11 @@
         "@types/node": "*"
       }
     },
+    "@types/hammerjs": {
+      "version": "2.0.36",
+      "resolved": "https://registry.npmjs.org/@types/hammerjs/-/hammerjs-2.0.36.tgz",
+      "integrity": "sha512-7TUK/k2/QGpEAv/BCwSHlYu3NXZhQ9ZwBYpzr9tjlPIL2C5BeGhH3DmVavRx3ZNyELX5TLC91JTz/cen6AAtIQ=="
+    },
     "@types/json-schema": {
       "version": "7.0.4",
       "resolved": "https://registry.npmjs.org/@types/json-schema/-/json-schema-7.0.4.tgz",
@@ -6487,6 +6492,11 @@
         "pify": "^4.0.1"
       }
     },
+    "hammerjs": {
+      "version": "2.0.8",
+      "resolved": "https://registry.npmjs.org/hammerjs/-/hammerjs-2.0.8.tgz",
+      "integrity": "sha1-BO93hiz/K7edMPdpIJWTAiK/YPE="
+    },
     "handle-thing": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/handle-thing/-/handle-thing-2.0.1.tgz",
diff --git a/viewer/package.json b/viewer/package.json
index 8f7de83..bc63dfd 100644
--- a/viewer/package.json
+++ b/viewer/package.json
@@ -13,8 +13,10 @@
     "@fortawesome/fontawesome-svg-core": "^1.2.28",
     "@fortawesome/free-solid-svg-icons": "^5.13.0",
     "@fortawesome/vue-fontawesome": "^0.1.9",
+    "@types/hammerjs": "^2.0.36",
     "buefy": "^0.8.15",
     "core-js": "^3.6.4",
+    "hammerjs": "^2.0.8",
     "resize-observer-polyfill": "^1.5.1",
     "v-lazy-image": "^1.4.0",
     "vue": "^2.6.11",
diff --git a/viewer/src/services/ldzoom.ts b/viewer/src/services/ldzoom.ts
index 61b5dc6..27debb5 100644
--- a/viewer/src/services/ldzoom.ts
+++ b/viewer/src/services/ldzoom.ts
@@ -19,25 +19,26 @@
 
 // polyfill still required for IE and Safari, see https://caniuse.com/#feat=resizeobserver
 import ResizeObserver from 'resize-observer-polyfill';
+import "hammerjs";
 
 /**
- * Mousewheel picture zoom helper.
+ * Mousewheel and pinch zoom handler.
  */
 export default class LdZoom {
   readonly containerElement: HTMLDivElement;
   readonly imageElement: HTMLImageElement;
   readonly maxScaleFactor: number;
-  readonly zoomSpeed: number;
+  readonly scrollZoomSpeed: number;
   scaleFactor: number = 0.0;
 
   constructor(
     containerElement: HTMLDivElement, imageElement: HTMLImageElement,
-    maxScaleFactor: number, zoomSpeed: number
+    maxScaleFactor: number, scrollZoomSpeed: number
   ) {
     this.containerElement = containerElement;
     this.imageElement = imageElement;
     this.maxScaleFactor = maxScaleFactor;
-    this.zoomSpeed = zoomSpeed;
+    this.scrollZoomSpeed = scrollZoomSpeed;
   }
 
   /**
@@ -52,10 +53,30 @@ export default class LdZoom {
 
     this.containerElement.addEventListener('wheel', wheelEvent => {
       wheelEvent.preventDefault();
-      this.zoom(wheelEvent);
+      const zoomDelta = -Math.sign(wheelEvent.deltaY) * this.scrollZoomSpeed;
+      this.zoom(wheelEvent.offsetX, wheelEvent.offsetY, zoomDelta);
     });
 
-    // TODO: handle pinch-to-zoom.
+    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);
+    });
   }
 
   /**
@@ -69,15 +90,12 @@ export default class LdZoom {
     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;
+  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 -= wheelEvent.offsetX - ratioX * this.imageElement.clientWidth;
-    this.containerElement.scrollTop -= wheelEvent.offsetY - ratioY * this.imageElement.clientHeight;
+    this.containerElement.scrollLeft -= focusX - ratioX * this.imageElement.clientWidth;
+    this.containerElement.scrollTop -= focusY - ratioY * this.imageElement.clientHeight;
   }
 
   private setImageScale(newScaleFactor: number) {
diff --git a/viewer/src/views/MainLayout.vue b/viewer/src/views/MainLayout.vue
index 6e707e6..c09e99a 100644
--- a/viewer/src/views/MainLayout.vue
+++ b/viewer/src/views/MainLayout.vue
@@ -87,6 +87,7 @@ body,
 html {
   height: 100%;
   overflow: hidden;
+  touch-action: none;
   background-color: $content-bgcolor;
   --layout-top: #{$layout-top};
   --layout-left: #{$layout-left};