From 221e69612fd8707ee47c2c9cda5af5f102e85c7d Mon Sep 17 00:00:00 2001
From: neverland <chenjiahan@buaa.edu.cn>
Date: Sat, 6 Oct 2018 16:26:39 +0800
Subject: [PATCH] [improvement] ImagePreview: support finger zooming (#1895)

---
 packages/image-preview/ImagePreview.vue | 149 ++++++++++++++++++++++--
 packages/image-preview/demo/index.vue   |   2 +-
 2 files changed, 142 insertions(+), 9 deletions(-)

diff --git a/packages/image-preview/ImagePreview.vue b/packages/image-preview/ImagePreview.vue
index cd4cdc207..9d6848f08 100644
--- a/packages/image-preview/ImagePreview.vue
+++ b/packages/image-preview/ImagePreview.vue
@@ -2,9 +2,9 @@
   <div
     v-if="value"
     :class="b()"
-    @touchstart="onTouchStart"
-    @touchend="onTouchEnd"
-    @touchcancel="onTouchEnd"
+    @touchstart="onWrapperTouchStart"
+    @touchend="onWrapperTouchEnd"
+    @touchcancel="onWrapperTouchEnd"
   >
     <div v-if="showIndex" :class="b('index')">{{ active + 1 }}/{{ count }}</div>
     <swipe
@@ -14,7 +14,15 @@
       @change="onChange"
     >
       <swipe-item v-for="(item, index) in images" :key="index">
-        <img :class="b('image')" :src="item" >
+        <img
+          :class="b('image')"
+          :src="item"
+          :style="index === active ? imageStyle : null"
+          @touchstart="onTouchStart"
+          @touchmove="onTouchMove"
+          @touchend="onTouchEnd"
+          @touchcancel="onTouchEnd"
+        >
       </swipe-item>
     </swipe>
   </div>
@@ -23,13 +31,18 @@
 <script>
 import create from '../utils/create';
 import Popup from '../mixins/popup';
+import Touch from '../mixins/touch';
 import Swipe from '../swipe';
 import SwipeItem from '../swipe-item';
+import { range } from '../utils';
+
+const MAX_ZOOM = 3;
+const MIN_ZOOM = 1 / 3;
 
 export default create({
   name: 'image-preview',
 
-  mixins: [Popup],
+  mixins: [Popup, Touch],
 
   components: {
     Swipe,
@@ -65,6 +78,11 @@ export default create({
 
   data() {
     return {
+      scale: 1,
+      moveX: 0,
+      moveY: 0,
+      moving: false,
+      zooming: false,
       active: this.startPosition
     };
   },
@@ -72,6 +90,20 @@ export default create({
   computed: {
     count() {
       return this.images.length;
+    },
+
+    imageStyle() {
+      const { scale } = this;
+      const style = {
+        transition: this.zooming || this.moving ? '' : '.3s all'
+      };
+
+      if (scale !== 1) {
+        style.transform = `scale3d(${scale}, ${scale}, 1) translate(${this
+          .moveX / scale}px, ${this.moveY / scale}px)`;
+      }
+
+      return style;
     }
   },
 
@@ -82,24 +114,125 @@ export default create({
   },
 
   methods: {
-    onTouchStart() {
+    onWrapperTouchStart() {
       this.touchStartTime = new Date();
     },
 
-    onTouchEnd(event) {
+    onWrapperTouchEnd(event) {
       event.preventDefault();
 
       const deltaTime = new Date() - this.touchStartTime;
       const { offsetX, offsetY } = this.$refs.swipe;
 
       // prevent long tap to close component
-      if (deltaTime < 500 && offsetX < 10 && offsetY < 10) {
+      if (deltaTime < 300 && offsetX < 10 && offsetY < 10) {
         this.$emit('input', false);
+        this.resetScale();
+      }
+    },
+
+    getDistance(touches) {
+      return Math.sqrt(
+        Math.abs(
+          (touches[0].clientX - touches[1].clientX) *
+            (touches[0].clientY - touches[1].clientY)
+        )
+      );
+    },
+
+    startMove(event) {
+      const image = event.currentTarget;
+      const rect = image.getBoundingClientRect();
+      const winWidth = window.innerWidth;
+      const winHeight = window.innerHeight;
+
+      this.touchStart(event);
+      this.moving = true;
+      this.startMoveX = this.moveX;
+      this.startMoveY = this.moveY;
+      this.maxMoveX = Math.max(0, (rect.width - winWidth) / 2);
+      this.maxMoveY = Math.max(0, (rect.height - winHeight) / 2);
+    },
+
+    startZoom(event) {
+      this.moving = false;
+      this.zooming = true;
+      this.startScale = this.scale;
+      this.startDistance = this.getDistance(event.touches);
+    },
+
+    onTouchStart(event) {
+      const { touches } = event;
+      const { offsetX } = this.$refs.swipe;
+      if (touches.length === 1 && this.scale !== 1) {
+        this.startMove(event);
+      } else if (touches.length === 2 && !offsetX) {
+        this.startZoom(event);
+      }
+    },
+
+    onTouchMove(event) {
+      const { touches } = event;
+      if (this.moving || this.zooming) {
+        event.preventDefault();
+        event.stopPropagation();
+      }
+
+      if (this.moving) {
+        this.touchMove(event);
+        const moveX = this.deltaX + this.startMoveX;
+        const moveY = this.deltaY + this.startMoveY;
+        this.moveX = range(moveX, -this.maxMoveX, this.maxMoveX);
+        this.moveY = range(moveY, -this.maxMoveY, this.maxMoveY);
+      }
+
+      if (this.zooming && touches.length === 2) {
+        const distance = this.getDistance(touches);
+        const scale = (this.startScale * distance) / this.startDistance;
+        this.scale = range(scale, MIN_ZOOM, MAX_ZOOM);
+      }
+    },
+
+    onTouchEnd(event) {
+      if (this.moving || this.zooming) {
+        let stopPropagation = true;
+
+        if (
+          this.moving &&
+          this.startMoveX === this.moveX &&
+          this.startMoveY === this.moveY
+        ) {
+          stopPropagation = false;
+        }
+
+        if (!event.touches.length) {
+          this.moving = false;
+          this.zooming = false;
+          this.startMoveX = 0;
+          this.startMoveY = 0;
+          this.startScale = 1;
+
+          if (this.scale < 1) {
+            this.resetScale();
+          }
+        }
+
+        if (stopPropagation) {
+          event.preventDefault();
+          event.stopPropagation();
+        }
       }
     },
 
     onChange(active) {
+      this.resetScale();
       this.active = active;
+    },
+
+    resetScale() {
+      this.scale = 1;
+      this.moveX = 0;
+      this.moveY = 0;
     }
   }
 });
diff --git a/packages/image-preview/demo/index.vue b/packages/image-preview/demo/index.vue
index e1c78e080..310a9b542 100644
--- a/packages/image-preview/demo/index.vue
+++ b/packages/image-preview/demo/index.vue
@@ -64,7 +64,7 @@ export default {
 
 .van-image-preview {
   img {
-    pointer-events: none;
+    -webkit-user-drag: none;
   }
 }
 </style>