fix(export): size wkhtmltopdf MathJax via scale, not the no-op minScale

Follow-up to c3e72cf. That commit plumbed a MathJax `minScale` option
to floor the auto font-match at 1.0 for the wkhtmltopdf export, based on
a wrong premise: MathJax v3's SVG output has no matchFontHeight, so
`minScale` never takes effect there.

Measuring rendered equation height across scale/minScale combinations in
Chromium (the same engine VNote's WebEngine uses to render the math that
is then handed to wkhtmltopdf) confirmed it: minScale 0.5, 1.0 and 1.25
render identically, while the math size tracks `scale` exactly (ratio ==
scale). So the only real effect of the previous change was dropping
scale 2.5 -> 1.0, which shrank math to Latin-text size -- too small next
to CJK glyphs in CJK-heavy notes.

- Revert the no-op mathJaxMinScale plumbing (struct fields in
  MarkdownWebGlobalOptions and MarkdownParas, the toJavascriptObject()
  emit, both generateMarkdownViewerTemplate builders, and the mathjax.js
  svg block).
- Set mathJaxScale = 1.5 for the wkhtmltopdf path only, so math renders
  at 1.5x body text: readable in print without the old 2.5x excess.
  Preview and Qt WebEngine printToPdf stay at the MathJax default (-1).
- Document in-code that scale is the only effective lever for SVG output
  so minScale is not reintroduced.

Author: tamlok

src/core/htmltemplatehelper.cpp

@@ -211,7 +211,6 @@ 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

@@ -54,12 +54,11 @@ struct MarkdownWebGlobalOptions {
   // This is just a hint not mandatory. For now, PlantUML and Graphviz needs this.
   bool m_transformSvgToPngEnabled = false;
 
-  // wkhtmltopdf mis-measures ex-height, shrinking MathJax to its minScale floor.
-  // m_mathJaxScale: global scale factor (-1 => MathJax default 1).
+  // wkhtmltopdf renders MathJax at the surrounding (Latin) text size, which looks too
+  // small next to CJK glyphs; the export path scales it up. -1 => MathJax default 1.
+  // NOTE: MathJax v3 SVG output has no matchFontHeight, so its `minScale` option is a
+  // no-op -- `scale` is the only effective lever (verified by measuring rendered height).
   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;
@@ -87,8 +86,6 @@ class HtmlTemplateHelper {
 
     qreal m_mathJaxScale = -1;
 
-    qreal m_mathJaxMinScale = -1;
-
     bool m_removeCodeToolBarEnabled = false;
   };
 

src/core/markdownwebglobaloptions.cpp

@@ -37,7 +37,6 @@ 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

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

src/export/webviewexporter.cpp

@@ -201,7 +201,6 @@ 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);
 
@@ -479,11 +478,12 @@ void WebViewExporter::prepare(const ExportOption &p_option) {
   paras.m_bodyWidth = pageBodySize.width();
   paras.m_bodyHeight = pageBodySize.height();
   paras.m_transformSvgToPngEnabled = p_option.m_transformSvgToPngEnabled;
-  // 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;
+  // wkhtmltopdf renders MathJax SVG at the surrounding Latin text size (scale x 1.0), which
+  // looks too small beside the larger CJK glyphs in CJK-heavy notes. Enlarge math to 1.5x
+  // body text for this export path only. `scale` is the ONLY effective lever here: MathJax
+  // v3 SVG output has no matchFontHeight, so the `minScale` option is a no-op (verified by
+  // measuring rendered equation height across scale/minScale combinations).
+  paras.m_mathJaxScale = useWkhtmltopdf ? 1.5 : -1;
   paras.m_removeCodeToolBarEnabled = p_option.m_removeCodeToolBarEnabled;
 
   m_htmlTemplate = generateMarkdownViewerTemplate(*configMgr, config, paras);