fix: 修复视频流画面闪烁问题

- canvas尺寸改为精确匹配bitmap尺寸,不再只增不减
- 仅在尺寸真正变化时才设置canvas.width/height(避免不必要的画布清空)
- 移除每帧绘制前的clearRect调用(消除透明闪烁)
- fit模式下用黑色fillRect替代clearRect填充边缘区域
- stretch模式下drawImage覆盖全画布,无需额外清除

src/components/Device/DeviceScreen.tsx

@@ -303,13 +303,13 @@ const DeviceScreen: React.FC<DeviceScreenProps> = ({ deviceId, onScreenSizeChang
             return
           }
 
-          // 只在canvas内部分辨率需要增大时才更新，避免偶发小帧清空画布导致闪烁
+          // canvas尺寸匹配bitmap，只在尺寸真正变化时才设置
-          if (canvas.width < bitmap.width || canvas.height < bitmap.height) {
+          // 注意：设置canvas.width/height会清空画布内容，所以必须紧接着绘制新帧
-            canvas.width = Math.max(canvas.width, bitmap.width)
+          const needsResize = canvas.width !== bitmap.width || canvas.height !== bitmap.height
-            canvas.height = Math.max(canvas.height, bitmap.height)
+          if (needsResize) {
+            canvas.width = bitmap.width
+            canvas.height = bitmap.height
           }
-          // 每帧绘制前清除（canvas可能比bitmap大）
-          ctx.clearRect(0, 0, canvas.width, canvas.height)
 
           switch (screenDisplay.fitMode) {
             case 'fit':
@@ -377,9 +377,16 @@ const DeviceScreen: React.FC<DeviceScreenProps> = ({ deviceId, onScreenSizeChang
 
   const drawFitMode = (ctx: CanvasRenderingContext2D, img: HTMLImageElement | ImageBitmap, canvas: HTMLCanvasElement) => {
     const scale = Math.min(canvas.width / img.width, canvas.height / img.height)
-    const x = (canvas.width - img.width * scale) / 2
+    const w = img.width * scale
-    const y = (canvas.height - img.height * scale) / 2
+    const h = img.height * scale
-    ctx.drawImage(img, x, y, img.width * scale, img.height * scale)
+    const x = (canvas.width - w) / 2
+    const y = (canvas.height - h) / 2
+    // 只清除图像未覆盖的边缘区域，避免全画布clearRect导致闪烁
+    if (x > 0 || y > 0) {
+      ctx.fillStyle = '#000'
+      ctx.fillRect(0, 0, canvas.width, canvas.height)
+    }
+    ctx.drawImage(img, x, y, w, h)
   }
 
   const drawFillMode = (ctx: CanvasRenderingContext2D, img: HTMLImageElement | ImageBitmap, canvas: HTMLCanvasElement) => {