fix: Canvas标题居中修复+字体加载等待

- 使用video元素实际渲染尺寸(clientWidth/clientHeight)替代容器尺寸
- 添加document.fonts.ready等待字体加载后再绘制
- 字体加载前跳过绘制避免measureText用fallback字体计算

apps/web/src/pages/generate/components/PreviewVideoPanel.tsx

@@ -3,7 +3,7 @@
  * Step3 生成预览后常驻显示预览视频
  * Step4+ 用 Canvas 绘制标题预览（替代 CSS overlay，与 ASS 渲染行为一致）
  */
-import React, { useRef, useEffect, useCallback } from "react"
+import React, { useRef, useEffect, useCallback, useState } from "react"
 import { PlayCircleOutlined, LoadingOutlined } from "@ant-design/icons"
 import type { PreviewResult, PreviewStatus } from "../hooks/useStep3Preview"
 import type { TitleSettings } from "../types"
@@ -46,8 +46,8 @@ function wrapText(ctx: CanvasRenderingContext2D, text: string, maxWidth: number)
 /**
  * 在 canvas 上绘制标题文字（含描边/阴影/多行居中）
  * @param ctx canvas 上下文
- * @param canvasWidth canvas CSS 宽度
- * @param canvasHeight canvas CSS 高度
+ * @param canvasWidth canvas CSS 宽度（绘制区域宽度）
+ * @param canvasHeight canvas CSS 高度（绘制区域高度）
  * @param text 标题文字
  * @param settings 标题样式
  * @param paddingX 左右边距（px），与 ASS 的 MarginL/MarginR 对应
@@ -128,7 +128,7 @@ function drawTitleOnCanvas(
       break
   }
 
-  // 逐行绘制
+  // 逐行绘制（水平居中于绘制区域）
   const x = w / 2
   lines.forEach((line, i) => {
     const y = startY + i * lineHeight
@@ -162,13 +162,17 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
   const isError = previewStatus === "error"
   const showTitlePreview = !!titleSettings
 
-  // video 模式 canvas ref
+  // video 模式 refs
   const canvasRef = useRef<HTMLCanvasElement>(null)
   const containerRef = useRef<HTMLDivElement>(null)
-  // no-video 模式 canvas ref
+  const videoRef = useRef<HTMLVideoElement>(null)
+  // no-video 模式 refs
   const noVideoCanvasRef = useRef<HTMLCanvasElement>(null)
   const noVideoContainerRef = useRef<HTMLDivElement>(null)
 
+  // 字体加载状态
+  const [fontLoaded, setFontLoaded] = useState(false)
+
   /** 在 video canvas 上绘制标题 */
   const drawVideoTitle = useCallback(() => {
     const canvas = canvasRef.current
@@ -180,17 +184,30 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
     const rect = container.getBoundingClientRect()
     if (rect.width <= 0 || rect.height <= 0) return
 
+    // 字体加载前跳过（等 fontLoaded 触发重绘）
+    if (!fontLoaded) return
+
+    // 优先使用 video 元素实际渲染尺寸，确保标题居中于视频画面
+    // 而非容器尺寸（容器可能比 video 元素更宽/更高）
+    const videoEl = videoRef.current
+    let drawW = rect.width
+    let drawH = rect.height
+    if (videoEl && videoEl.clientWidth > 0 && videoEl.clientHeight > 0) {
+      drawW = videoEl.clientWidth
+      drawH = videoEl.clientHeight
+    }
+
     drawTitleOnCanvas(
       ctx,
-      rect.width,
-      rect.height,
+      drawW,
+      drawH,
       titleText || "",
       titleSettings,
       40,
       titleSettings.position,
       60,
     )
-  }, [titleText, titleSettings])
+  }, [titleText, titleSettings, fontLoaded])
 
   /** 在 no-video canvas 上绘制标题 */
   const drawNoVideoTitle = useCallback(() => {
@@ -203,6 +220,9 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
     const rect = container.getBoundingClientRect()
     if (rect.width <= 0 || rect.height <= 0) return
 
+    // 字体加载前跳过
+    if (!fontLoaded) return
+
     // no-video 容器较窄，字号缩小 + 减少边距
     drawTitleOnCanvas(
       ctx,
@@ -215,7 +235,7 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
       30,
       0.75,
     )
-  }, [titleText, titleSettings])
+  }, [titleText, titleSettings, fontLoaded])
 
   // video 模式：ResizeObserver 监听容器尺寸变化 → 重绘
   useEffect(() => {
@@ -227,7 +247,6 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
       drawVideoTitle()
     })
     observer.observe(container)
-    // 初始绘制（延迟一帧等容器渲染完成）
     requestAnimationFrame(drawVideoTitle)
 
     return () => observer.disconnect()
@@ -248,6 +267,22 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
     return () => observer.disconnect()
   }, [showTitlePreview, hasPreview, isError, drawNoVideoTitle])
 
+  // 字体加载完成后重绘（Canvas measureText 依赖字体已加载）
+  useEffect(() => {
+    if (!showTitlePreview) return
+    let cancelled = false
+    document.fonts.ready.then(() => {
+      if (cancelled) return
+      // 短暂延迟确保字体完全可用
+      setTimeout(() => {
+        if (!cancelled) setFontLoaded(true)
+      }, 50)
+    })
+    return () => {
+      cancelled = true
+    }
+  }, [showTitlePreview])
+
   // video 加载完成后重绘
   const handleVideoLoaded = useCallback(() => {
     if (showTitlePreview) {
@@ -285,7 +320,10 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
             </div>
           </div>
           <div className="xx-preview-progress-bar-wrap">
-            <div className="xx-preview-progress-fill" style={{ width: `${progress}%` }} />
+            <div
+              className="xx-preview-progress-fill"
+              style={{ width: `${progress}%` }}
+            />
           </div>
         </div>
       )}
@@ -310,6 +348,7 @@ export const PreviewVideoPanel: React.FC<PreviewVideoPanelProps> = ({
         <div ref={containerRef} style={{ position: "relative" }}>
           <div className="xx-preview-video">
             <video
+              ref={videoRef}
               src={previewResult.videoUrl}
               controls
               preload="metadata"