feat: v0.5.0 —— 导出 PDF（带预览窗口）

导出
- 文件 → 导出 PDF…（Ctrl+E）先弹出预览窗口，确认后点「保存 PDF…」选路径
- A4 纸、16mm 页边距；预览和导出共用同一个 QTextDocument，页宽一致
- 只用 Qt 自带的 QPrinter / QTextDocument，没有引入外部 PDF 库

排版
- 新增 MarkdownRenderer：把 Markdown 解析成排版好的富文本文档
- 支持标题、列表 / 任务列表、引用、围栏代码块、行内代码、
  粗体 / 斜体 / 删除线、链接；图片输出 alt 文字，表格暂按原文
- 代码块带底色、引用带竖线、分隔线画成横线

其它
- 用用户更新后的 logo.png 重新生成了 ico / icns / png
- docs/screenshot-export.png 与 README 同步

README.md

@@ -2,7 +2,7 @@
 
 一个轻量的跨平台 Markdown 编辑器，基于 **Qt 5 / C++17** 构建。
 
-当前版本 **0.4.0**。
+当前版本 **0.5.0**。
 
 ## 界面
 
@@ -14,6 +14,10 @@
 
 ![源代码模式](docs/screenshot-source.png)
 
+导出 PDF 前先给一个预览窗口，确认无误再选路径保存：
+
+![导出 PDF](docs/screenshot-export.png)
+
 ## 功能
 
 ### 编辑
@@ -56,6 +60,16 @@
 
 按钮在源码模式下会变成 `</src>`。
 
+### 导出 PDF
+
+**文件 → 导出 PDF…**（`Ctrl+E`）会先弹出预览窗口，里面就是最终排版；
+点「保存 PDF…」选个位置即可。A4 纸、16mm 页边距，预览和导出用的是同一份
+排版文档，所见即所得。
+
+导出用的是 Qt 自带的 `QPrinter` + `QTextDocument`，不需要额外的 PDF 库。
+支持标题、列表（含任务列表）、引用、代码块、行内代码、粗体 / 斜体 / 删除线、
+链接；图片只输出 alt 文字，表格暂时按原文输出。
+
 ### 文件
 
 - 新建、打开、保存、另存为、最近打开（最多 8 条）
@@ -152,6 +166,7 @@ VoiletMark --screenshot a.png  # 渲染窗口截图后退出（调试 / 视觉
 | `Ctrl+N` / `Ctrl+O` / `Ctrl+S` | 新建 / 打开 / 保存 |
 | `Ctrl+Shift+S` | 另存为 |
 | `Ctrl+Shift+O` | 打开文件夹 |
+| `Ctrl+E` | 导出 PDF（先预览） |
 | `Ctrl+B` | 显示 / 隐藏侧栏 |
 | `Ctrl+Shift+M` | 源代码模式 |
 | `Ctrl+1` ~ `Ctrl+6` | 设为 1–6 级标题（再按取消） |
@@ -170,7 +185,9 @@ src/
 ├── ThemeManager.{h,cpp}   四种主题模式 + 系统检测 + 调色板 / QSS 生成
 ├── MainWindow.{h,cpp}     菜单、文件读写、文件夹侧栏、状态栏、设置
 ├── MarkdownEditor.{h,cpp} 编辑器控件：行号、缩进、标题 / 代码块命令、源码模式
-└── MarkdownHighlighter.{h,cpp}  Markdown 着色与就地渲染（隐藏标记、标题缩放）
+├── MarkdownHighlighter.{h,cpp}  Markdown 着色与就地渲染（隐藏标记、标题缩放）
+├── MarkdownRenderer.{h,cpp}     导出用的 Markdown → 富文本文档转换
+└── ExportDialog.{h,cpp}         PDF 预览与保存对话框
 
 logo.png              图标源文件
 resources.qrc         窗口图标资源

VoiletMark.pro

@@ -1,8 +1,8 @@
 TEMPLATE = app
 TARGET   = VoiletMark
-VERSION  = 0.4.0
+VERSION  = 0.5.0
 
-QT += core gui widgets
+QT += core gui widgets printsupport
 
 CONFIG += c++17 warn_on
 
@@ -22,12 +22,16 @@ SOURCES += \
     src/MainWindow.cpp \
     src/MarkdownEditor.cpp \
     src/MarkdownHighlighter.cpp \
+    src/MarkdownRenderer.cpp \
+    src/ExportDialog.cpp \
     src/ThemeManager.cpp
 
 HEADERS += \
     src/MainWindow.h \
     src/MarkdownEditor.h \
     src/MarkdownHighlighter.h \
+    src/MarkdownRenderer.h \
+    src/ExportDialog.h \
     src/ThemeManager.h
 
 # Linux 桌面集成：make install 之后能在应用菜单里找到

src/ExportDialog.cpp

@@ -0,0 +1,107 @@
+#include "ExportDialog.h"
+
+#include "MarkdownRenderer.h"
+
+#include <QDir>
+#include <QFileDialog>
+#include <QFileInfo>
+#include <QHBoxLayout>
+#include <QLabel>
+#include <QMessageBox>
+#include <QPageSize>
+#include <QPrinter>
+#include <QPushButton>
+#include <QTextBrowser>
+#include <QTextDocument>
+#include <QVBoxLayout>
+
+ExportDialog::ExportDialog(const QString &markdown, const QString &documentName,
+                           const QString &startDirectory, QWidget *parent)
+    : QDialog(parent)
+    , m_documentName(documentName)
+    , m_startDirectory(startDirectory)
+{
+    setWindowTitle(tr("导出 PDF — %1")
+                       .arg(documentName.isEmpty() ? tr("未命名") : documentName));
+    resize(900, 840);
+
+    QVBoxLayout *layout = new QVBoxLayout(this);
+    layout->setContentsMargins(16, 16, 16, 12);
+    layout->setSpacing(10);
+
+    m_document = new QTextDocument(this);
+    MarkdownRenderer::render(markdown, m_document);
+    // A4 去掉 16mm 页边距后的正文宽度（96dpi 下的像素）：
+    // 预览和打印用同一个页宽，看到的就是导出的样子。
+    m_document->setPageSize(QSizeF(672.76, 1001.57));
+
+    m_preview = new QTextBrowser(this);
+    m_preview->setFrameShape(QFrame::NoFrame);
+    m_preview->setOpenExternalLinks(true);
+    m_preview->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
+    m_preview->setFixedWidth(700);
+    m_preview->setDocument(m_document);
+    m_preview->setStyleSheet(QStringLiteral(
+        "QTextBrowser { background: #ffffff; color: #1f2328;"
+        " border: 1px solid #d8dde3; border-radius: 4px; }"));
+
+    QHBoxLayout *center = new QHBoxLayout;
+    center->addStretch(1);
+    center->addWidget(m_preview);
+    center->addStretch(1);
+    layout->addLayout(center, 1);
+
+    QLabel *hint = new QLabel(tr("A4 纸、16mm 页边距，内容和预览一致。"), this);
+    hint->setForegroundRole(QPalette::PlaceholderText);
+
+    QPushButton *saveButton = new QPushButton(tr("保存 PDF…"), this);
+    saveButton->setDefault(true);
+    QPushButton *closeButton = new QPushButton(tr("关闭"), this);
+
+    QHBoxLayout *buttons = new QHBoxLayout;
+    buttons->addWidget(hint);
+    buttons->addStretch(1);
+    buttons->addWidget(closeButton);
+    buttons->addWidget(saveButton);
+    layout->addLayout(buttons);
+
+    connect(closeButton, &QPushButton::clicked, this, &QDialog::reject);
+    connect(saveButton, &QPushButton::clicked, this, &ExportDialog::savePdf);
+}
+
+void ExportDialog::savePdf()
+{
+    QString suggested = m_documentName.isEmpty()
+                            ? tr("未命名")
+                            : QFileInfo(m_documentName).completeBaseName();
+    suggested += QStringLiteral(".pdf");
+
+    QString target = QFileDialog::getSaveFileName(
+        this, tr("保存 PDF"), QDir(m_startDirectory).filePath(suggested),
+        tr("PDF 文件 (*.pdf)"));
+    if (target.isEmpty())
+        return;
+
+    if (!target.endsWith(QStringLiteral(".pdf"), Qt::CaseInsensitive))
+        target += QStringLiteral(".pdf");
+
+    QPrinter printer(QPrinter::HighResolution);
+    printer.setOutputFormat(QPrinter::PdfFormat);
+    printer.setOutputFileName(target);
+    printer.setPageSize(QPageSize(QPageSize::A4));
+    printer.setPageMargins(QMarginsF(16, 16, 16, 16), QPageLayout::Millimeter);
+    printer.setDocName(QFileInfo(target).completeBaseName());
+
+    m_document->print(&printer);
+
+    if (!QFileInfo::exists(target) || QFileInfo(target).size() <= 0) {
+        QMessageBox::warning(this, tr("导出失败"),
+                             tr("没能写出「%1」，换个位置再试一次。")
+                                 .arg(QDir::toNativeSeparators(target)));
+        return;
+    }
+
+    QMessageBox::information(this, tr("导出完成"),
+                             tr("已保存到\n%1").arg(QDir::toNativeSeparators(target)));
+    accept();
+}

src/ExportDialog.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <QDialog>
+
+class QTextBrowser;
+class QTextDocument;
+
+/// “导出 PDF”窗口：上方是排版后的预览，下方保存为 PDF。
+class ExportDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    ExportDialog(const QString &markdown, const QString &documentName,
+                 const QString &startDirectory, QWidget *parent = nullptr);
+
+private:
+    void savePdf();
+
+    QTextBrowser *m_preview = nullptr;
+    QTextDocument *m_document = nullptr;
+    QString m_documentName;
+    QString m_startDirectory;
+};

src/MainWindow.cpp

@@ -1,5 +1,6 @@
 #include "MainWindow.h"
 
+#include "ExportDialog.h"
 #include "MarkdownEditor.h"
 #include "ThemeManager.h"
 
@@ -133,6 +134,10 @@ void MainWindow::createActions()
     m_saveAsAction->setShortcut(QKeySequence(QStringLiteral("Ctrl+Shift+S")));
     connect(m_saveAsAction, &QAction::triggered, this, [this] { saveFileAs(); });
 
+    m_exportPdfAction = new QAction(tr("导出 PDF…"), this);
+    m_exportPdfAction->setShortcut(QKeySequence(QStringLiteral("Ctrl+E")));
+    connect(m_exportPdfAction, &QAction::triggered, this, &MainWindow::exportPdf);
+
     m_quitAction = new QAction(tr("退出"), this);
     m_quitAction->setShortcut(QKeySequence::Quit);
     connect(m_quitAction, &QAction::triggered, this, &QWidget::close);
@@ -269,6 +274,7 @@ void MainWindow::createMenus()
     fileMenu->addSeparator();
     fileMenu->addAction(m_saveAction);
     fileMenu->addAction(m_saveAsAction);
+    fileMenu->addAction(m_exportPdfAction);
     fileMenu->addSeparator();
     fileMenu->addAction(m_quitAction);
 
@@ -536,6 +542,12 @@ bool MainWindow::saveFileAs()
     return writeToFile(path);
 }
 
+void MainWindow::exportPdf()
+{
+    ExportDialog dialog(m_editor->toPlainText(), displayName(), startDirectory(), this);
+    dialog.exec();
+}
+
 bool MainWindow::writeToFile(const QString &path)
 {
     QString text = m_editor->toPlainText();

src/MainWindow.h

@@ -56,6 +56,7 @@ private:
     void selectInSidebar(const QString &path);
     QStringList scanFolder() const;
     void setSourceModeEnabled(bool enabled);
+    void exportPdf();
 
     void changeZoom(int direction);
     void resetZoom();
@@ -92,6 +93,7 @@ private:
     QAction *m_openAction = nullptr;
     QAction *m_saveAction = nullptr;
     QAction *m_saveAsAction = nullptr;
+    QAction *m_exportPdfAction = nullptr;
     QAction *m_quitAction = nullptr;
 
     QAction *m_undoAction = nullptr;

src/MarkdownRenderer.cpp

@@ -0,0 +1,405 @@
+#include "MarkdownRenderer.h"
+
+#include <QColor>
+#include <QFont>
+#include <QRegularExpression>
+#include <QTextBlockFormat>
+#include <QTextCharFormat>
+#include <QTextCursor>
+#include <QTextDocument>
+
+namespace {
+
+QStringList proseFamilies()
+{
+    return {QStringLiteral("Noto Sans CJK SC"), QStringLiteral("Source Han Sans SC"),
+            QStringLiteral("WenQuanYi Micro Hei"), QStringLiteral("Microsoft YaHei"),
+            QStringLiteral("PingFang SC"), QStringLiteral("Segoe UI"),
+            QStringLiteral("DejaVu Sans")};
+}
+
+QStringList monoFamilies()
+{
+    return {QStringLiteral("JetBrains Mono"), QStringLiteral("Cascadia Code"),
+            QStringLiteral("Source Han Mono SC"), QStringLiteral("Noto Sans Mono CJK SC"),
+            QStringLiteral("Sarasa Mono SC"), QStringLiteral("Consolas"),
+            QStringLiteral("DejaVu Sans Mono")};
+}
+
+QColor hex(const char *value)
+{
+    return QColor(QString::fromLatin1(value));
+}
+
+struct Style
+{
+    QColor text = hex("#1f2328");
+    QColor heading = hex("#11151a");
+    QColor muted = hex("#5b6570");
+    QColor rule = hex("#d0d7de");
+    QColor codeText = hex("#b4295a");
+    QColor codeBg = hex("#f3f4f6");
+    QColor link = hex("#0969da");
+    QColor marker = hex("#0969da");
+};
+
+constexpr qreal kBodySize = 11.5;
+constexpr qreal kCodeSize = 10.5;
+
+class Renderer
+{
+public:
+    explicit Renderer(QTextDocument *document)
+        : m_document(document)
+        , m_cursor(document)
+    {
+    }
+
+    void run(const QString &markdown);
+
+private:
+    void beginBlock(const QTextBlockFormat &blockFormat, const QTextCharFormat &charFormat);
+    void renderHeading(int level, const QString &text);
+    void renderParagraph(const QString &text, int quoteDepth);
+    void renderListItem(const QString &marker, const QString &text, int indentLevel);
+    void renderCodeBlock(const QStringList &lines);
+    void renderRule();
+    void renderInline(const QString &text, const QTextCharFormat &base);
+
+    QTextCharFormat bodyFormat(const QColor &color = QColor()) const;
+    QTextCharFormat codeFormat() const;
+
+    QTextDocument *m_document = nullptr;
+    QTextCursor m_cursor;
+    bool m_firstBlock = true;
+    Style m_style;
+};
+
+QTextCharFormat Renderer::bodyFormat(const QColor &color) const
+{
+    QTextCharFormat format;
+    format.setFontFamilies(proseFamilies());
+    format.setFontPointSize(kBodySize);
+    format.setForeground(color.isValid() ? color : m_style.text);
+    return format;
+}
+
+QTextCharFormat Renderer::codeFormat() const
+{
+    QTextCharFormat format;
+    format.setFontFamilies(monoFamilies());
+    format.setFontFixedPitch(true);
+    format.setFontPointSize(kCodeSize);
+    format.setForeground(m_style.codeText);
+    format.setBackground(m_style.codeBg);
+    return format;
+}
+
+void Renderer::beginBlock(const QTextBlockFormat &blockFormat, const QTextCharFormat &charFormat)
+{
+    if (m_firstBlock) {
+        m_cursor.setBlockFormat(blockFormat);
+        m_cursor.setBlockCharFormat(charFormat);
+        m_firstBlock = false;
+    } else {
+        m_cursor.insertBlock(blockFormat, charFormat);
+    }
+    m_cursor.setCharFormat(charFormat);
+}
+
+void Renderer::renderHeading(int level, const QString &text)
+{
+    static const qreal scales[6] = {2.0, 1.55, 1.3, 1.15, 1.05, 1.0};
+    QTextBlockFormat blockFormat;
+    blockFormat.setLineHeight(135, QTextBlockFormat::ProportionalHeight);
+    blockFormat.setTopMargin(level <= 2 ? 20 : 14);
+    blockFormat.setBottomMargin(8);
+
+    QTextCharFormat format;
+    format.setFontFamilies(proseFamilies());
+    format.setFontPointSize(kBodySize * scales[qBound(1, level, 6) - 1]);
+    format.setFontWeight(QFont::Bold);
+    format.setForeground(m_style.heading);
+
+    beginBlock(blockFormat, format);
+    m_cursor.insertText(text, format);
+}
+
+void Renderer::renderParagraph(const QString &text, int quoteDepth)
+{
+    QTextBlockFormat blockFormat;
+    blockFormat.setLineHeight(150, QTextBlockFormat::ProportionalHeight);
+    blockFormat.setBottomMargin(8);
+    if (quoteDepth > 0) {
+        blockFormat.setLeftMargin(18 + (quoteDepth - 1) * 16);
+    }
+    beginBlock(blockFormat, bodyFormat(quoteDepth > 0 ? m_style.muted : QColor()));
+
+    if (quoteDepth > 0) {
+        QTextCharFormat bar = bodyFormat(m_style.rule);
+        bar.setFontWeight(QFont::Bold);
+        m_cursor.insertText(QStringLiteral("│ "), bar);
+    }
+    renderInline(text, bodyFormat(quoteDepth > 0 ? m_style.muted : QColor()));
+}
+
+void Renderer::renderListItem(const QString &marker, const QString &text, int indentLevel)
+{
+    QTextBlockFormat blockFormat;
+    blockFormat.setLineHeight(150, QTextBlockFormat::ProportionalHeight);
+    blockFormat.setBottomMargin(6);
+    blockFormat.setLeftMargin(18 + indentLevel * 18);
+    blockFormat.setTextIndent(-14);
+    beginBlock(blockFormat, bodyFormat());
+
+    QTextCharFormat markerFormat = bodyFormat(m_style.marker);
+    markerFormat.setFontWeight(QFont::DemiBold);
+    m_cursor.insertText(marker + QLatin1Char(' '), markerFormat);
+    renderInline(text, bodyFormat());
+}
+
+void Renderer::renderCodeBlock(const QStringList &lines)
+{
+    QTextBlockFormat blockFormat;
+    blockFormat.setLineHeight(135, QTextBlockFormat::ProportionalHeight);
+    blockFormat.setTopMargin(6);
+    blockFormat.setBottomMargin(10);
+    blockFormat.setLeftMargin(14);
+    blockFormat.setRightMargin(14);
+    blockFormat.setBackground(m_style.codeBg);
+
+    const QTextCharFormat format = codeFormat();
+    QStringList content = lines;
+    if (content.isEmpty())
+        content << QString();
+
+    for (int index = 0; index < content.size(); ++index) {
+        QTextBlockFormat lineFormat = blockFormat;
+        lineFormat.setTopMargin(index == 0 ? 6 : 0);
+        lineFormat.setBottomMargin(index == content.size() - 1 ? 10 : 0);
+        beginBlock(lineFormat, format);
+        const QString line = content.at(index);
+        m_cursor.insertText(line.isEmpty() ? QStringLiteral(" ") : line, format);
+    }
+}
+
+void Renderer::renderRule()
+{
+    QTextBlockFormat blockFormat;
+    blockFormat.setLineHeight(140, QTextBlockFormat::ProportionalHeight);
+    blockFormat.setTopMargin(6);
+    blockFormat.setBottomMargin(12);
+    beginBlock(blockFormat, bodyFormat(m_style.rule));
+
+    QTextCharFormat format = bodyFormat(m_style.rule);
+    format.setFontPointSize(8);
+    m_cursor.insertText(QString(60, QChar(0x2500)), format);
+}
+
+void Renderer::renderInline(const QString &text, const QTextCharFormat &base)
+{
+    struct Rule {
+        QRegularExpression pattern;
+        int kind;
+    };
+
+    static const QVector<Rule> rules = {
+        {QRegularExpression(QStringLiteral("`([^`\\n]+)`")), 0},
+        {QRegularExpression(QStringLiteral("!\\[([^\\]]*)\\]\\(([^)]*)\\)")), 1},
+        {QRegularExpression(QStringLiteral("\\[([^\\]]*)\\]\\(([^)]*)\\)")), 2},
+        {QRegularExpression(QStringLiteral("\\*\\*\\*([^*]+)\\*\\*\\*")), 3},
+        {QRegularExpression(QStringLiteral("\\*\\*([^*]+)\\*\\*")), 4},
+        {QRegularExpression(QStringLiteral("__([^_]+)__")), 4},
+        {QRegularExpression(QStringLiteral("\\*([^*]+)\\*")), 5},
+        {QRegularExpression(QStringLiteral("(?<![_\\w])_([^_]+)_(?![_\\w])")), 5},
+        {QRegularExpression(QStringLiteral("~~([^~]+)~~")), 6},
+        {QRegularExpression(QStringLiteral("<(https?://[^>]+)>")), 7},
+    };
+
+    int position = 0;
+    while (position < text.size()) {
+        int bestStart = -1;
+        int bestKind = -1;
+        QRegularExpressionMatch best;
+        for (const Rule &rule : rules) {
+            const QRegularExpressionMatch match = rule.pattern.match(text, position);
+            if (!match.hasMatch())
+                continue;
+            if (bestStart < 0 || match.capturedStart() < bestStart) {
+                bestStart = match.capturedStart();
+                bestKind = rule.kind;
+                best = match;
+            }
+        }
+
+        if (bestStart < 0) {
+            m_cursor.insertText(text.mid(position), base);
+            break;
+        }
+        if (bestStart > position)
+            m_cursor.insertText(text.mid(position, bestStart - position), base);
+
+        const QString content = best.capturedLength(1) > 0 ? best.captured(1) : best.captured(0);
+        switch (bestKind) {
+        case 0: { // 行内代码
+            m_cursor.insertText(content, codeFormat());
+            break;
+        }
+        case 1: { // 图片：显示 alt
+            QTextCharFormat format = base;
+            format.setForeground(m_style.muted);
+            format.setFontItalic(true);
+            m_cursor.insertText(content.isEmpty() ? QStringLiteral("[图片]") : content, format);
+            break;
+        }
+        case 2: { // 链接
+            QTextCharFormat format = base;
+            format.setForeground(m_style.link);
+            format.setFontUnderline(true);
+            format.setAnchor(true);
+            format.setAnchorHref(best.captured(2));
+            m_cursor.insertText(best.captured(1), format);
+            break;
+        }
+        case 3: { // 粗斜体
+            QTextCharFormat format = base;
+            format.setFontWeight(QFont::Bold);
+            format.setFontItalic(true);
+            m_cursor.insertText(content, format);
+            break;
+        }
+        case 4: { // 粗体
+            QTextCharFormat format = base;
+            format.setFontWeight(QFont::Bold);
+            format.setForeground(m_style.heading);
+            m_cursor.insertText(content, format);
+            break;
+        }
+        case 5: { // 斜体
+            QTextCharFormat format = base;
+            format.setFontItalic(true);
+            m_cursor.insertText(content, format);
+            break;
+        }
+        case 6: { // 删除线
+            QTextCharFormat format = base;
+            format.setFontStrikeOut(true);
+            format.setForeground(m_style.muted);
+            m_cursor.insertText(content, format);
+            break;
+        }
+        default: { // 裸链接
+            QTextCharFormat format = base;
+            format.setForeground(m_style.link);
+            format.setFontUnderline(true);
+            format.setAnchor(true);
+            format.setAnchorHref(best.captured(1));
+            m_cursor.insertText(best.captured(1), format);
+            break;
+        }
+        }
+
+        position = bestStart + best.capturedLength();
+    }
+}
+
+void Renderer::run(const QString &markdown)
+{
+    const QStringList lines = markdown.split(QLatin1Char('\n'));
+
+    static const QRegularExpression headingPattern(QStringLiteral("^(#{1,6})\\s+(.*)$"));
+    static const QRegularExpression fencePattern(QStringLiteral("^\\s{0,3}(?:```|~~~)(.*)$"));
+    static const QRegularExpression quotePattern(QStringLiteral("^\\s{0,3}(>+)\\s?(.*)$"));
+    static const QRegularExpression bulletPattern(
+        QStringLiteral("^(\\s*)[-+*]\\s+\\[([ xX])\\]\\s?(.*)$"));
+    static const QRegularExpression listPattern(
+        QStringLiteral("^(\\s*)([-+*]|\\d{1,9}[.)])\\s+(.*)$"));
+    static const QRegularExpression rulePattern(
+        QStringLiteral("^\\s{0,3}(?:(?:\\*\\s*){3,}|(?:-\\s*){3,}|(?:_\\s*){3,})$"));
+
+    int index = 0;
+    while (index < lines.size()) {
+        const QString line = lines.at(index);
+
+        const QRegularExpressionMatch fence = fencePattern.match(line);
+        if (fence.hasMatch()) {
+            QStringList code;
+            ++index;
+            while (index < lines.size() && !fencePattern.match(lines.at(index)).hasMatch())
+                code << lines.at(index++);
+            if (index < lines.size())
+                ++index; // 跳过闭合围栏
+            renderCodeBlock(code);
+            continue;
+        }
+
+        if (line.trimmed().isEmpty()) {
+            ++index;
+            continue;
+        }
+
+        const QRegularExpressionMatch heading = headingPattern.match(line);
+        if (heading.hasMatch()) {
+            renderHeading(heading.capturedLength(1), heading.captured(2).trimmed());
+            ++index;
+            continue;
+        }
+
+        if (rulePattern.match(line).hasMatch()) {
+            renderRule();
+            ++index;
+            continue;
+        }
+
+        const QRegularExpressionMatch quote = quotePattern.match(line);
+        if (quote.hasMatch()) {
+            renderParagraph(quote.captured(2).trimmed(), quote.capturedLength(1));
+            ++index;
+            continue;
+        }
+
+        const QRegularExpressionMatch task = bulletPattern.match(line);
+        if (task.hasMatch()) {
+            const int indent = task.captured(1).size() / 2;
+            const bool done = task.captured(2).compare(QLatin1String("x"), Qt::CaseInsensitive) == 0;
+            renderListItem(done ? QStringLiteral("☑") : QStringLiteral("☐"),
+                           task.captured(3), indent);
+            ++index;
+            continue;
+        }
+
+        const QRegularExpressionMatch list = listPattern.match(line);
+        if (list.hasMatch()) {
+            const int indent = list.captured(1).size() / 2;
+            QString marker = list.captured(2);
+            if (marker.size() == 1 && (marker == QLatin1String("-") || marker == QLatin1String("+")
+                                       || marker == QLatin1String("*")))
+                marker = QStringLiteral("•");
+            renderListItem(marker, list.captured(3), indent);
+            ++index;
+            continue;
+        }
+
+        renderParagraph(line, 0);
+        ++index;
+    }
+}
+
+} // namespace
+
+void MarkdownRenderer::render(const QString &markdown, QTextDocument *document)
+{
+    if (!document)
+        return;
+
+    document->clear();
+
+    QFont body;
+    body.setFamilies(proseFamilies());
+    body.setPointSizeF(kBodySize);
+    document->setDefaultFont(body);
+    document->setDocumentMargin(0);
+
+    Renderer renderer(document);
+    renderer.run(markdown);
+}

src/MarkdownRenderer.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <QString>
+
+class QTextDocument;
+
+/// 把 Markdown 渲染成排版好的 QTextDocument，供导出预览和打印 PDF 共用。
+/// 不依赖任何外部库，只是在这里做一遍块级 / 行内解析。
+namespace MarkdownRenderer {
+
+void render(const QString &markdown, QTextDocument *document);
+
+} // namespace MarkdownRenderer