fix: 优化邀请函画布导出分辨率，提升图片与文字清晰度

js/script.js

@@ -1958,24 +1958,40 @@
         const ctx = canvas.getContext('2d');
         const container = imageContainer;
 
-        const width = container.clientWidth;
-        const height = container.clientHeight;
+        // 高清渲染倍数
+        const scaleFactor = 2;
+        
+        // 显示尺寸
+        const displayWidth = container.clientWidth;
+        const displayHeight = container.clientHeight;
+        
+        // 高清画布尺寸（2倍）
+        const width = displayWidth * scaleFactor;
+        const height = displayHeight * scaleFactor;
 
         canvas.width = width;
         canvas.height = height;
 
+        // 启用高清渲染
+        ctx.imageSmoothingEnabled = true;
+        ctx.imageSmoothingQuality = 'high';
+
         ctx.fillStyle = '#fff';
         ctx.fillRect(0, 0, width, height);
 
+        // 计算缩放比例
+        const scaleX = width / displayWidth;
+        const scaleY = height / displayHeight;
+
         if (currentImage) {
-            drawBgImageOnCanvas(ctx, currentImage, width, height);
+            drawBgImageOnCanvasHD(ctx, currentImage, width, height, scaleX, scaleY);
         }
 
-        await drawOverlayImages(ctx);
+        await drawOverlayImagesHD(ctx, scaleX, scaleY);
 
         const textInputs = container.querySelectorAll('.preview-input-layer .text-input');
         textInputs.forEach(textInput => {
-            drawTextOnCanvas(ctx, textInput);
+            drawTextOnCanvasHD(ctx, textInput, scaleX, scaleY);
         });
 
         return canvas;
@@ -2013,6 +2029,39 @@
         ctx.globalAlpha = 1;
     }
 
+    // 绘制背景图（高清版本）
+    function drawBgImageOnCanvasHD(ctx, img, canvasWidth, canvasHeight, scaleX, scaleY) {
+        // 使用原始图片尺寸进行高清渲染
+        const containerWidth = canvasWidth;
+        const containerHeight = canvasHeight;
+        const imgRatio = img.naturalWidth / img.naturalHeight;
+        const containerRatio = containerWidth / containerHeight;
+
+        let imgWidth, imgHeight;
+
+        if (imgRatio > containerRatio) {
+            imgHeight = containerHeight;
+            imgWidth = imgHeight * imgRatio;
+        } else {
+            imgWidth = containerWidth;
+            imgHeight = imgWidth / imgRatio;
+        }
+
+        // 应用缩放
+        const scaledWidth = imgWidth * bgImageScale;
+        const scaledHeight = imgHeight * bgImageScale;
+
+        // 计算位置（考虑高清缩放）
+        const baseLeft = (containerWidth - scaledWidth) / 2;
+        const drawX = baseLeft + (imageOffsetX * scaleX);
+        const drawY = (containerHeight - scaledHeight) / 2;
+
+        ctx.globalAlpha = bgImageOpacity;
+        // 使用原始图片绘制，获得最佳清晰度
+        ctx.drawImage(img, drawX, drawY, scaledWidth, scaledHeight);
+        ctx.globalAlpha = 1;
+    }
+
     // 绘制层叠图
     function drawOverlayImages(ctx) {
         return new Promise((resolve) => {
@@ -2059,6 +2108,56 @@
         });
     }
 
+    // 绘制层叠图（高清版本）
+    function drawOverlayImagesHD(ctx, scaleX, scaleY) {
+        return new Promise((resolve) => {
+            const overlayImages = overlayLayer.querySelectorAll('.overlay-image');
+            if (overlayImages.length === 0) {
+                resolve();
+                return;
+            }
+
+            let loadedCount = 0;
+            const totalImages = overlayImages.length;
+            
+            function checkComplete() {
+                loadedCount++;
+                if (loadedCount >= totalImages) {
+                    resolve();
+                }
+            }
+            
+            overlayImages.forEach(overlayEl => {
+                const imgEl = overlayEl.querySelector('img');
+                if (!imgEl) {
+                    checkComplete();
+                    return;
+                }
+
+                // 使用 offsetLeft/offsetTop 获取相对于 overlayLayer 的位置，并应用高清缩放
+                const left = overlayEl.offsetLeft * scaleX;
+                const top = overlayEl.offsetTop * scaleY;
+                const width = overlayEl.offsetWidth * scaleX;
+                const height = overlayEl.offsetHeight * scaleY;
+
+                ctx.globalAlpha = overlayEl.style.opacity || 1;
+
+                const img = new Image();
+                img.crossOrigin = 'anonymous';
+                img.onload = () => {
+                    ctx.drawImage(img, left, top, width, height);
+                    ctx.globalAlpha = 1;
+                    checkComplete();
+                };
+                img.onerror = () => {
+                    ctx.globalAlpha = 1;
+                    checkComplete();
+                };
+                img.src = imgEl.src;
+            });
+        });
+    }
+
     // 在画布上绘制文字
     function drawTextOnCanvas(ctx, inputElement) {
         const deleteBtn = inputElement.querySelector('.text-delete-btn');
@@ -2088,6 +2187,35 @@
         ctx.fillText(text, inputLeft, inputTop + textOffsetY);
     }
 
+    // 在画布上绘制文字（高清版本）
+    function drawTextOnCanvasHD(ctx, inputElement, scaleX, scaleY) {
+        const deleteBtn = inputElement.querySelector('.text-delete-btn');
+        let text = inputElement.textContent;
+        if (deleteBtn) {
+            text = text.replace(deleteBtn.textContent, '');
+        }
+        if (!text.trim()) return;
+
+        // 使用 offsetLeft/offsetTop 获取相对于 preview-input-layer 的位置，并应用高清缩放
+        const inputLeft = inputElement.offsetLeft * scaleX;
+        const inputTop = inputElement.offsetTop * scaleY;
+
+        const style = window.getComputedStyle(inputElement);
+        const fontSize = parseInt(style.fontSize) * scaleX; // 字体大小也按比例缩放
+        const lineHeight = parseFloat(style.lineHeight);
+        
+        // 使用高清字体渲染
+        ctx.font = `${style.fontWeight} ${fontSize}px ${style.fontFamily}`;
+        ctx.fillStyle = style.color;
+        ctx.textBaseline = 'alphabetic';
+
+        // 计算文本垂直偏移量，使其与 DOM 渲染一致
+        const actualLineHeight = (lineHeight || fontSize * 1.4) * scaleY;
+        const textOffsetY = (actualLineHeight - fontSize) / 2 + fontSize * 0.85;
+
+        ctx.fillText(text, inputLeft, inputTop + textOffsetY);
+    }
+
     // 保存图片
     async function saveImage() {
         if (!currentImage) {