feat: 新增右键/长按预览功能，保留原有操作样式

js/script.js

@@ -522,6 +522,14 @@
         menu.style.left = x + 'px';
         menu.style.top = y + 'px';
 
+        const previewItem = document.createElement('div');
+        previewItem.className = 'context-menu-item';
+        previewItem.textContent = '预览图片';
+        previewItem.addEventListener('click', () => {
+            showPreview();
+            hideContextMenu();
+        });
+
         const copyItem = document.createElement('div');
         copyItem.className = 'context-menu-item';
         copyItem.textContent = '复制图片';
@@ -538,11 +546,72 @@
             hideContextMenu();
         });
 
+        menu.appendChild(previewItem);
         menu.appendChild(copyItem);
         menu.appendChild(saveItem);
         document.body.appendChild(menu);
     }
 
+    // 显示预览
+    async function showPreview() {
+        const canvas = await generateCanvas();
+        const dataUrl = canvas.toDataURL('image/png');
+
+        const tipOverlay = document.createElement('div');
+        tipOverlay.id = 'previewTip';
+        tipOverlay.style.cssText = `
+            position: fixed;
+            top: 0;
+            left: 0;
+            right: 0;
+            bottom: 0;
+            background: rgba(0,0,0,0.9);
+            display: flex;
+            flex-direction: column;
+            align-items: center;
+            justify-content: center;
+            z-index: 10000;
+            padding: 20px;
+        `;
+
+        const tipText = document.createElement('p');
+        tipText.textContent = '预览图片';
+        tipText.style.cssText = `
+            color: #fff;
+            font-size: 18px;
+            margin-bottom: 20px;
+            text-align: center;
+        `;
+
+        const img = document.createElement('img');
+        img.src = dataUrl;
+        img.style.cssText = `
+            max-width: 100%;
+            max-height: 80vh;
+            border-radius: 8px;
+            box-shadow: 0 4px 20px rgba(255,255,255,0.2);
+        `;
+
+        const closeBtn = document.createElement('button');
+        closeBtn.textContent = '关闭';
+        closeBtn.style.cssText = `
+            margin-top: 20px;
+            padding: 12px 40px;
+            font-size: 16px;
+            background: #fff;
+            color: #333;
+            border: none;
+            border-radius: 25px;
+            cursor: pointer;
+        `;
+        closeBtn.onclick = () => tipOverlay.remove();
+
+        tipOverlay.appendChild(tipText);
+        tipOverlay.appendChild(img);
+        tipOverlay.appendChild(closeBtn);
+        document.body.appendChild(tipOverlay);
+    }
+
     // 隐藏右键菜单
     function hideContextMenu() {
         const existingMenu = document.getElementById('contextMenu');
@@ -741,6 +810,28 @@
         savePanel.appendChild(cancelBtn);
         tipOverlay.appendChild(savePanel);
         document.body.appendChild(tipOverlay);
+
+        // 添加预览按钮
+        const previewBtn = document.createElement('button');
+        previewBtn.textContent = '预览图片';
+        previewBtn.style.cssText = `
+            width: 100%;
+            padding: 16px;
+            font-size: 16px;
+            background: #34C759;
+            color: #fff;
+            border: none;
+            border-radius: 10px;
+            cursor: pointer;
+            margin-bottom: 12px;
+        `;
+        previewBtn.onclick = () => {
+            tipOverlay.remove();
+            showPreview();
+        };
+
+        // 插入到标题后面
+        savePanel.insertBefore(previewBtn, saveBtn);
     }
 
     // 窗口大小改变时更新图片位置和边界