fix(PdfViewer): 改进缩放功能以保持视图中心位置

重构缩放逻辑，使用比例计算代替直接缩放比率，确保缩放时视图中心位置保持不变
移除平滑滚动以避免偏移抖动，直接设置滚动位置

@@ -354,28 +354,40 @@ const handleClose = () => {
  */
 const zoomIn = () => {
     if (zoomLevel.value < 3) { // 最大放大到300%
-        // 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 oldW = pdfContainer.scrollWidth;
+            const oldH = pdfContainer.scrollHeight;
+            const viewportW = pdfContainer.clientWidth;
+            const viewportH = pdfContainer.clientHeight;
+
+            const centerX = pdfContainer.scrollLeft + viewportW / 2;
+            const centerY = pdfContainer.scrollTop + viewportH / 2;
+
+            const anchorRatioX = oldW > 0 ? centerX / oldW : 0;
+            const anchorRatioY = oldH > 0 ? centerY / oldH : 0;
 
-            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'
-                });
+                const newW = pdfContainer.scrollWidth;
+                const newH = pdfContainer.scrollHeight;
+
+                let targetCenterX = newW * anchorRatioX;
+                let targetCenterY = newH * anchorRatioY;
+
+                let newScrollLeft = Math.max(0, targetCenterX - viewportW / 2);
+                let newScrollTop = Math.max(0, targetCenterY - viewportH / 2);
+
+                newScrollLeft = Math.min(newScrollLeft, Math.max(0, newW - viewportW));
+                newScrollTop = Math.min(newScrollTop, Math.max(0, newH - viewportH));
+
+                // 直接赋值避免平滑滚动导致的偏移抖动
+                pdfContainer.scrollLeft = newScrollLeft;
+                pdfContainer.scrollTop = newScrollTop;
             });
+        } else {
+            zoomLevel.value = Math.min(3, zoomLevel.value + 0.25);
         }
     }
 };
@@ -385,28 +397,39 @@ const zoomIn = () => {
  */
 const zoomOut = () => {
     if (zoomLevel.value > 0.5) { // 最小缩小到50%
-        // 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 oldW = pdfContainer.scrollWidth;
+            const oldH = pdfContainer.scrollHeight;
+            const viewportW = pdfContainer.clientWidth;
+            const viewportH = pdfContainer.clientHeight;
+
+            const centerX = pdfContainer.scrollLeft + viewportW / 2;
+            const centerY = pdfContainer.scrollTop + viewportH / 2;
+
+            const anchorRatioX = oldW > 0 ? centerX / oldW : 0;
+            const anchorRatioY = oldH > 0 ? centerY / oldH : 0;
 
-            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'
-                });
+                const newW = pdfContainer.scrollWidth;
+                const newH = pdfContainer.scrollHeight;
+
+                let targetCenterX = newW * anchorRatioX;
+                let targetCenterY = newH * anchorRatioY;
+
+                let newScrollLeft = Math.max(0, targetCenterX - viewportW / 2);
+                let newScrollTop = Math.max(0, targetCenterY - viewportH / 2);
+
+                newScrollLeft = Math.min(newScrollLeft, Math.max(0, newW - viewportW));
+                newScrollTop = Math.min(newScrollTop, Math.max(0, newH - viewportH));
+
+                pdfContainer.scrollLeft = newScrollLeft;
+                pdfContainer.scrollTop = newScrollTop;
             });
+        } else {
+            zoomLevel.value = Math.max(0.5, zoomLevel.value - 0.25);
         }
     }
 };
@@ -417,15 +440,10 @@ const zoomOut = () => {
 const resetZoom = () => {
     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'
-            });
+            pdfContainer.scrollLeft = 0;
+            pdfContainer.scrollTop = 0;
         });
     } else {
         zoomLevel.value = 1;