test: 焦点锚定容差按实际每行字数算，不再写死字符数

src/_test/electron/reader-features.integration.js

@@ -1373,7 +1373,7 @@ app.whenReady().then(async () => {
     return progress && progress.locator && progress.locator.kind === 'epub';
   }, 5000);
   const epubProgress = readerStore.getState(entry.id).progress;
-  const focalOffsetAfter = await js(epubWin, `(() => {
+  const focalAfter = await js(epubWin, `(() => {
     const frame = document.querySelector('.host-epub iframe');
     const doc = frame.contentDocument;
     const outerRect = document.querySelector('.epub-scroll').getBoundingClientRect();
@@ -1387,18 +1387,31 @@ app.whenReady().then(async () => {
       const range = doc.caretRangeFromPoint(x, y);
       if (range) caret = { offsetNode: range.startContainer, offset: range.startOffset };
     }
-    if (!caret) return -1;
+    if (!caret) return { offset: -1, charsPerLine: 0 };
+    // 容差要按"一行有多少字"算：字体不同，同样的一行在不同平台字数不同，
+    // 写死字符数的话换个字体集就会假失败
+    let charsPerLine = 0;
+    const host = caret.offsetNode.parentElement;
+    if (host && host.textContent) {
+      const range = doc.createRange();
+      range.selectNodeContents(host);
+      const lines = range.getClientRects().length;
+      if (lines > 0) charsPerLine = host.textContent.length / lines;
+    }
     const walker = doc.createTreeWalker(doc.body, NodeFilter.SHOW_TEXT);
     let offset = 0;
     for (let node = walker.nextNode(); node; node = walker.nextNode()) {
-      if (node === caret.offsetNode) return offset + caret.offset;
+      if (node === caret.offsetNode) return { offset: offset + caret.offset, charsPerLine };
       offset += node.data.length;
     }
-    return -1;
+    return { offset: -1, charsPerLine };
   })()`);
+  const focalOffsetAfter = focalAfter.offset;
+  // 焦点锚定的语义是"停在原来那行附近"，超过一行就说明锚点真的漂了
+  const focalTolerance = Math.max(12, Math.ceil(focalAfter.charsPerLine));
   check('EPUB 双指缩放保持焦点附近字符偏移',
-    Math.abs(focalOffsetAfter - pinchResult.anchorOffset) <= 12,
+    Math.abs(focalOffsetAfter - pinchResult.anchorOffset) <= focalTolerance,
-    `${pinchResult.anchorOffset} -> ${focalOffsetAfter}; 顶部=${epubProgress.locator.offset}`);
+    `${pinchResult.anchorOffset} -> ${focalOffsetAfter}; 容差=${focalTolerance}; 顶部=${epubProgress.locator.offset}`);
 
   const epubSelection = await selectEpubText(epubWin);
   await waitForJs(epubWin, `!document.getElementById('selBar').classList.contains('hidden')`);