fix(export): correct wkhtmltopdf MathJax sizing with minScale floor

wkhtmltopdf's old headless Qt-4 WebKit mis-measures the surrounding
text's ex-height, so MathJax shrinks each equation to its minScale
floor (0.5). The previous fix blindly multiplied by a magic scale of
2.5, which combined with that floor over-enlarged math to ~1.25x the
surrounding text.

Replace the magic 2.5 with a root-cause fix: raise MathJax's SVG
minScale floor to 1.0 so math cannot be shrunk below text size, and
drop scale back to its default. Scoped to the wkhtmltopdf export path
only; on-screen preview and the Qt WebEngine printToPdf path are
behaviorally unchanged (they emit the -1 sentinel and fall back to
MathJax's default 0.5).

- Plumb a new mathJaxMinScale global option exactly like mathJaxScale
  (MarkdownWebGlobalOptions + MarkdownParas, both generateMarkdownViewer
  Template copies, and toJavascriptObject()).
- mathjax.js: honor window.vxOptions.mathJaxMinScale, defaulting to
  MathJax's documented 0.5 when absent (sentinel -1).
- webviewexporter: set mathJaxMinScale = 1.0 for wkhtmltopdf and -1
  otherwise; set mathJaxScale = -1 (removing the 2.5).

Author: tamlok

src/core/htmltemplatehelper.cpp

@@ -211,6 +211,7 @@ QString HtmlTemplateHelper::generateMarkdownViewerTemplate(const MarkdownEditorC
     opts.m_bodyHeight = p_paras.m_bodyHeight;
     opts.m_transformSvgToPngEnabled = p_paras.m_transformSvgToPngEnabled;
     opts.m_mathJaxScale = p_paras.m_mathJaxScale;
+    opts.m_mathJaxMinScale = p_paras.m_mathJaxMinScale;
     opts.m_removeCodeToolBarEnabled = p_paras.m_removeCodeToolBarEnabled;
     fillGlobalOptions(htmlTemplate, opts);
   }

src/core/htmltemplatehelper.h

@@ -54,8 +54,12 @@ struct MarkdownWebGlobalOptions {
   // This is just a hint not mandatory. For now, PlantUML and Graphviz needs this.
   bool m_transformSvgToPngEnabled = false;
 
-  // wkhtmltopdf will make the MathJax formula too small.
+  // wkhtmltopdf mis-measures ex-height, shrinking MathJax to its minScale floor.
+  // m_mathJaxScale: global scale factor (-1 => MathJax default 1).
   qreal m_mathJaxScale = -1;
+  // m_mathJaxMinScale: floor for MathJax's text-matching scale (-1 => MathJax default 0.5).
+  // Set to 1 for wkhtmltopdf export so math is not shrunk below text size.
+  qreal m_mathJaxMinScale = -1;
 
   // Whether remove the tool bar of code blocks added by Prism.js.
   bool m_removeCodeToolBarEnabled = false;
@@ -83,6 +87,8 @@ class HtmlTemplateHelper {
 
     qreal m_mathJaxScale = -1;
 
+    qreal m_mathJaxMinScale = -1;
+
     bool m_removeCodeToolBarEnabled = false;
   };
 

src/core/markdownwebglobaloptions.cpp

@@ -37,6 +37,7 @@ QString MarkdownWebGlobalOptions::toJavascriptObject() const {
          QStringLiteral("transformSvgToPngEnabled: %1,\n")
              .arg(Utils::boolToString(m_transformSvgToPngEnabled)) +
          QStringLiteral("mathJaxScale: %1,\n").arg(m_mathJaxScale) +
+         QStringLiteral("mathJaxMinScale: %1,\n").arg(m_mathJaxMinScale) +
          QStringLiteral("removeCodeToolBarEnabled: %1,\n")
              .arg(Utils::boolToString(m_removeCodeToolBarEnabled)) +
          QStringLiteral("sectionNumberBaseLevel: %1\n").arg(m_sectionNumberBaseLevel) +

src/data/extra/web/js/mathjax.js

@@ -19,7 +19,8 @@ window.MathJax = {
     svg: {
         // Make SVG self-contained.
         fontCache: 'local',
-        scale: window.vxOptions.mathJaxScale > 0 ? window.vxOptions.mathJaxScale : 1
+        scale: window.vxOptions.mathJaxScale > 0 ? window.vxOptions.mathJaxScale : 1,
+        minScale: window.vxOptions.mathJaxMinScale > 0 ? window.vxOptions.mathJaxMinScale : 0.5
     }
 };
 

src/export/webviewexporter.cpp

@@ -201,6 +201,7 @@ QString generateMarkdownViewerTemplate(ConfigMgr2 &p_configMgr,
   opts.m_bodyHeight = p_paras.m_bodyHeight;
   opts.m_transformSvgToPngEnabled = p_paras.m_transformSvgToPngEnabled;
   opts.m_mathJaxScale = p_paras.m_mathJaxScale;
+  opts.m_mathJaxMinScale = p_paras.m_mathJaxMinScale;
   opts.m_removeCodeToolBarEnabled = p_paras.m_removeCodeToolBarEnabled;
   fillGlobalOptions(htmlTemplate, opts);
 
@@ -478,7 +479,11 @@ void WebViewExporter::prepare(const ExportOption &p_option) {
   paras.m_bodyWidth = pageBodySize.width();
   paras.m_bodyHeight = pageBodySize.height();
   paras.m_transformSvgToPngEnabled = p_option.m_transformSvgToPngEnabled;
-  paras.m_mathJaxScale = useWkhtmltopdf ? 2.5 : -1;
+  // wkhtmltopdf's old WebKit mis-measures the surrounding text's ex-height, so MathJax
+  // shrinks each equation to its minScale floor (0.5). Raise that floor to 1.0 instead of
+  // blindly multiplying by 2.5 (which over-enlarged math to 1.25x text).
+  paras.m_mathJaxScale = -1;
+  paras.m_mathJaxMinScale = useWkhtmltopdf ? 1.0 : -1;
   paras.m_removeCodeToolBarEnabled = p_option.m_removeCodeToolBarEnabled;
 
   m_htmlTemplate = generateMarkdownViewerTemplate(*configMgr, config, paras);