feat(PdfViewer): 添加缩放时保持滚动位置功能

在PDF查看器中添加滚动位置记录功能，当用户进行缩放操作时，会基于当前视口中心点计算并保持相对滚动位置，提升用户体验

@@ -110,6 +110,7 @@ const loadingProgress = ref(0);
 const loadingError = ref(false);
 const errorMessage = ref('');
 const zoomLevel = ref(1); // 缩放级别，1为100%
+const scrollPosition = ref({ x: 0, y: 0 }); // 记录滚动位置
 
 /**
  * 监听show属性变化，控制PDF加载
@@ -171,7 +172,14 @@ const handleComplete = () => {
  * @param {number} scrollOffset - 滚动偏移量
  */
 const handleScroll = (scrollOffset) => {
-    // 可以在这里处理滚动事件
+    // 记录当前滚动位置
+    const pdfContainer = document.querySelector('.pdf-viewer-container .pdf-content');
+    if (pdfContainer) {
+        scrollPosition.value = {
+            x: pdfContainer.scrollLeft,
+            y: pdfContainer.scrollTop
+        };
+    }
 };
 
 /**
@@ -237,7 +245,29 @@ const retryLoad = () => {
  */
 const zoomIn = () => {
     if (zoomLevel.value < 3) { // 最大放大到300%
-        zoomLevel.value = Math.min(3, zoomLevel.value + 0.25);
+        // 记录缩放前的滚动位置
+        const pdfContainer = document.querySelector('.pdf-viewer-container .pdf-content');
+        if (pdfContainer) {
+            const centerX = pdfContainer.scrollLeft + pdfContainer.clientWidth / 2;
+            const centerY = pdfContainer.scrollTop + pdfContainer.clientHeight / 2;
+            
+            const oldZoom = zoomLevel.value;
+            zoomLevel.value = Math.min(3, zoomLevel.value + 0.25);
+            const newZoom = zoomLevel.value;
+            
+            // 使用nextTick确保DOM更新后再调整滚动位置
+            nextTick(() => {
+                const zoomRatio = newZoom / oldZoom;
+                const newScrollLeft = centerX * zoomRatio - pdfContainer.clientWidth / 2;
+                const newScrollTop = centerY * zoomRatio - pdfContainer.clientHeight / 2;
+                
+                pdfContainer.scrollTo({
+                    left: Math.max(0, newScrollLeft),
+                    top: Math.max(0, newScrollTop),
+                    behavior: 'smooth'
+                });
+            });
+        }
     }
 };
 
@@ -246,7 +276,29 @@ const zoomIn = () => {
  */
 const zoomOut = () => {
     if (zoomLevel.value > 0.5) { // 最小缩小到50%
-        zoomLevel.value = Math.max(0.5, zoomLevel.value - 0.25);
+        // 记录缩放前的滚动位置
+        const pdfContainer = document.querySelector('.pdf-viewer-container .pdf-content');
+        if (pdfContainer) {
+            const centerX = pdfContainer.scrollLeft + pdfContainer.clientWidth / 2;
+            const centerY = pdfContainer.scrollTop + pdfContainer.clientHeight / 2;
+            
+            const oldZoom = zoomLevel.value;
+            zoomLevel.value = Math.max(0.5, zoomLevel.value - 0.25);
+            const newZoom = zoomLevel.value;
+            
+            // 使用nextTick确保DOM更新后再调整滚动位置
+            nextTick(() => {
+                const zoomRatio = newZoom / oldZoom;
+                const newScrollLeft = centerX * zoomRatio - pdfContainer.clientWidth / 2;
+                const newScrollTop = centerY * zoomRatio - pdfContainer.clientHeight / 2;
+                
+                pdfContainer.scrollTo({
+                    left: Math.max(0, newScrollLeft),
+                    top: Math.max(0, newScrollTop),
+                    behavior: 'smooth'
+                });
+            });
+        }
     }
 };
 
@@ -254,7 +306,21 @@ const zoomOut = () => {
  * 重置缩放
  */
 const resetZoom = () => {
-    zoomLevel.value = 1;
+    const pdfContainer = document.querySelector('.pdf-viewer-container .pdf-content');
+    if (pdfContainer) {
+        // 重置到顶部中央位置
+        zoomLevel.value = 1;
+        
+        nextTick(() => {
+            pdfContainer.scrollTo({
+                left: 0,
+                top: 0,
+                behavior: 'smooth'
+            });
+        });
+    } else {
+        zoomLevel.value = 1;
+    }
 };
 
 /**