fix：优化导出图片清晰度

js/script.js

@@ -1781,7 +1781,12 @@
     // 显示预览
     async function showPreview() {
         const canvas = await generateCanvas();
-        const dataUrl = canvas.toDataURL('image/png');
+        console.log('预览画布尺寸:', canvas.width, 'x', canvas.height);
+        
+        // 使用 toBlob 获取更高质量的图片
+        const blob = await new Promise(resolve => canvas.toBlob(resolve, 'image/png', 1.0));
+        console.log('预览图片大小:', (blob.size / 1024).toFixed(2), 'KB');
+        const dataUrl = URL.createObjectURL(blob);
 
         const tipOverlay = document.createElement('div');
         tipOverlay.id = 'previewTip';
@@ -1969,6 +1974,7 @@
         // 设置画布为固定高清分辨率
         canvas.width = TARGET_WIDTH;
         canvas.height = TARGET_HEIGHT;
+        console.log('设置画布尺寸:', canvas.width, 'x', canvas.height);
 
         // 启用最高质量渲染
         ctx.imageSmoothingEnabled = true;
@@ -2224,7 +2230,7 @@
 
         try {
             const canvas = await generateCanvas();
-            showMobileSaveTip();
+            await showMobileSaveTip();
         } catch (err) {
             console.error('保存失败:', err);
             alert('保存失败，请重试');
@@ -2232,9 +2238,14 @@
     }
 
     // 显示移动端保存选项
-    function showMobileSaveTip() {
+    async function showMobileSaveTip() {
         const canvas = exportCanvas;
-        const dataUrl = canvas.toDataURL('image/png');
+        console.log('导出画布尺寸:', canvas.width, 'x', canvas.height);
+        
+        // 使用 toBlob 获取更高质量的图片
+        const blob = await new Promise(resolve => canvas.toBlob(resolve, 'image/png', 1.0));
+        console.log('导出图片大小:', (blob.size / 1024).toFixed(2), 'KB');
+        const dataUrl = URL.createObjectURL(blob);
         const filename = '邀请函_' + Date.now() + '.png';
 
         const tipOverlay = document.createElement('div');