From d05972d229ac9a2c5029fc44e891e8cd9ac0e068 Mon Sep 17 00:00:00 2001
From: inottn <inottn@outlook.com>
Date: Sun, 14 May 2023 21:51:19 +0800
Subject: [PATCH] feat(ImagePreview): use the touched point as the center of
 zooming (#11848)

---
 .../src/image-preview/ImagePreviewItem.tsx    | 56 ++++++++++++++-----
 1 file changed, 42 insertions(+), 14 deletions(-)

diff --git a/packages/vant/src/image-preview/ImagePreviewItem.tsx b/packages/vant/src/image-preview/ImagePreviewItem.tsx
index a224c37aa..4a3b056cb 100644
--- a/packages/vant/src/image-preview/ImagePreviewItem.tsx
+++ b/packages/vant/src/image-preview/ImagePreviewItem.tsx
@@ -20,7 +20,7 @@ import {
 
 // Composables
 import { useTouch } from '../composables/use-touch';
-import { useEventListener } from '@vant/use';
+import { useEventListener, useRect } from '@vant/use';
 
 // Components
 import { Image } from '../image';
@@ -33,6 +33,11 @@ const getDistance = (touches: TouchList) =>
       (touches[0].clientY - touches[1].clientY) ** 2
   );
 
+const getCenter = (touches: TouchList) => ({
+  x: (touches[0].clientX + touches[1].clientX) / 2,
+  y: (touches[0].clientY + touches[1].clientY) / 2,
+});
+
 const bem = createNamespace('image-preview')[1];
 
 export default defineComponent({
@@ -62,6 +67,7 @@ export default defineComponent({
     });
 
     const touch = useTouch();
+    const imageRef = ref<ComponentInstance>();
     const swipeItem = ref<ComponentInstance>();
 
     const vertical = computed(() => {
@@ -77,9 +83,8 @@ export default defineComponent({
       };
 
       if (scale !== 1) {
-        const offsetX = moveX / scale;
-        const offsetY = moveY / scale;
-        style.transform = `scale(${scale}, ${scale}) translate(${offsetX}px, ${offsetY}px)`;
+        // use matrix to solve the problem of elements not rendering due to safari optimization
+        style.transform = `matrix(${scale}, 0, 0, ${scale}, ${moveX}, ${moveY})`;
       }
 
       return style;
@@ -111,11 +116,31 @@ export default defineComponent({
       return 0;
     });
 
-    const setScale = (scale: number) => {
+    const setScale = (scale: number, center?: { x: number; y: number }) => {
       scale = clamp(scale, +props.minZoom, +props.maxZoom + 1);
 
       if (scale !== state.scale) {
+        const ratio = scale / state.scale;
         state.scale = scale;
+
+        if (center) {
+          const imageRect = useRect(imageRef.value?.$el);
+          const origin = {
+            x: imageRect.width * 0.5,
+            y: imageRect.height * 0.5,
+          };
+          const moveX =
+            state.moveX - (center.x - imageRect.left - origin.x) * (ratio - 1);
+          const moveY =
+            state.moveY - (center.y - imageRect.top - origin.y) * (ratio - 1);
+
+          state.moveX = clamp(moveX, -maxMoveX.value, maxMoveX.value);
+          state.moveY = clamp(moveY, -maxMoveY.value, maxMoveY.value);
+        } else {
+          state.moveX = 0;
+          state.moveY = 0;
+        }
+
         emit('scale', {
           scale,
           index: props.active,
@@ -125,16 +150,17 @@ export default defineComponent({
 
     const resetScale = () => {
       setScale(1);
-      state.moveX = 0;
-      state.moveY = 0;
     };
 
     const toggleScale = () => {
       const scale = state.scale > 1 ? 1 : 2;
 
-      setScale(scale);
-      state.moveX = 0;
-      state.moveY = 0;
+      setScale(
+        scale,
+        scale === 2
+          ? { x: touch.startX.value, y: touch.startY.value }
+          : undefined
+      );
     };
 
     let fingerNum: number;
@@ -142,6 +168,7 @@ export default defineComponent({
     let startMoveY: number;
     let startScale: number;
     let startDistance: number;
+    let lastCenter: { x: number; y: number };
     let doubleTapTimer: ReturnType<typeof setTimeout> | null;
     let touchStartTime: number;
     let isImageMoved = false;
@@ -170,7 +197,7 @@ export default defineComponent({
 
       if (state.zooming) {
         startScale = state.scale;
-        startDistance = getDistance(event.touches);
+        startDistance = getDistance(touches);
       }
     };
 
@@ -207,8 +234,8 @@ export default defineComponent({
         if (touches.length === 2) {
           const distance = getDistance(touches);
           const scale = (startScale * distance) / startDistance;
-
-          setScale(scale);
+          lastCenter = getCenter(touches);
+          setScale(scale, lastCenter);
         }
       }
     };
@@ -279,7 +306,7 @@ export default defineComponent({
 
           const maxZoom = +props.maxZoom;
           if (state.scale > maxZoom) {
-            state.scale = maxZoom;
+            setScale(maxZoom, lastCenter);
           }
         }
       }
@@ -331,6 +358,7 @@ export default defineComponent({
           ) : (
             <Image
               v-slots={imageSlots}
+              ref={imageRef}
               src={props.src}
               fit="contain"
               class={bem('image', { vertical: vertical.value })}