TechDraw: Fix font size issues when exporting to SVG

src/Mod/TechDraw/Gui/DlgPrefsTechDraw.ui

@@ -707,7 +707,7 @@
            <string>View Label size in units</string>
           </property>
           <property name="value">
-           <double>6.000000000000000</double>
+           <double>8.000000000000000</double>
           </property>
           <property name="prefEntry" stdset="0">
            <cstring>LabelSize</cstring>

src/Mod/TechDraw/Gui/DlgPrefsTechDraw2.ui

@@ -259,7 +259,7 @@
            <string>Dimension font size in units</string>
           </property>
           <property name="value">
-           <double>3.500000000000000</double>
+           <double>5.000000000000000</double>
           </property>
           <property name="prefEntry" stdset="0">
            <cstring>FontSize</cstring>

src/Mod/TechDraw/Gui/MDIViewPage.cpp

@@ -1374,4 +1374,13 @@ void MDIViewPage::showStatusMsg(const char* s1, const char* s2, const char* s3)
     }
 }
 
+MDIViewPage *MDIViewPage::getFromScene(const QGraphicsScene *scene)
+{
+    if (scene != nullptr && scene->parent() != nullptr) {
+        return dynamic_cast<MDIViewPage *>(scene->parent());
+    }
+
+    return nullptr;
+}
+
 #include <Mod/TechDraw/Gui/moc_MDIViewPage.cpp>

src/Mod/TechDraw/Gui/MDIViewPage.h

@@ -71,7 +71,7 @@ class TechDrawGuiExport MDIViewPage : public Gui::MDIView, public Gui::Selection
     void matchSceneRectToTemplate(void);
 
     bool onMsg(const char* pMsg,const char** ppReturn);
-      bool onHasMsg(const char* pMsg) const;
+    bool onHasMsg(const char* pMsg) const;
 
     void print();
     void print(QPrinter* printer);
@@ -101,6 +101,8 @@ class TechDrawGuiExport MDIViewPage : public Gui::MDIView, public Gui::Selection
 
     bool addView(const App::DocumentObject *obj);
 
+    static MDIViewPage *getFromScene(const QGraphicsScene *scene);
+
 public Q_SLOTS:
     void viewAll();
     void saveSVG(void);

src/Mod/TechDraw/Gui/QGCustomLabel.cpp

@@ -77,23 +77,5 @@ void QGCustomLabel::paint ( QPainter * painter, const QStyleOptionGraphicsItem *
     QStyleOptionGraphicsItem myOption(*option);
     myOption.state &= ~QStyle::State_Selected;
 
-    //see QGCustomText for explanation of this code
-    double dppt = 3.53;
-    double svgMagicX = Rez::guiX(8.0);
-    double svgMagicY = Rez::guiX(12.0);
-    double svgMagicYoffset = Rez::guiX(3.0);
-    double fontSize = Rez::appX(font().pointSizeF());
-    double ty = svgMagicY + (svgMagicYoffset*fontSize)/dppt;
-    QPointF svgMove(-svgMagicX/dppt,ty);
-
-    QPaintDevice* hw = painter->device();
-    QSvgGenerator* svg = dynamic_cast<QSvgGenerator*>(hw);
-    if (svg) {
-        painter->scale(Rez::appX(dppt),Rez::appX(dppt));
-        painter->translate(svgMove);
-    } else {
-        painter->scale(1.0,1.0);
-    }
-
     QGraphicsTextItem::paint (painter, &myOption, widget);
 }

src/Mod/TechDraw/Gui/QGCustomText.cpp

@@ -131,32 +131,6 @@ void QGCustomText::paint ( QPainter * painter, const QStyleOptionGraphicsItem *
     QStyleOptionGraphicsItem myOption(*option);
     myOption.state &= ~QStyle::State_Selected;
 
-    //svg text is much larger than screen text.  scene units(mm or 0.1mm in hirez) vs points.
-    //need to scale text if going to svg.
-    //TODO: magic translation happens. why? approx: right ~8mm  down: 12mm + (3mm per mm of text height)
-    //SVG transform matrix translation values are different for same font size + different fonts (Sans vs Ubuntu vs Arial)???
-    //                     scale values are same for same font size + different fonts.
-    //calculate dots/mm 
-    //in hirez - say factor = 10, we have 10 dpmm in scene space. 
-    //  so 254dpi / 72pts/in  => 3.53 dppt 
-    double dpmm = 3.53;         //dots/pt
-    double svgMagicX = Rez::guiX(8.0);                      //8mm -> 80 gui dots
-    double svgMagicY = Rez::guiX(12.0);
-    double svgMagicYoffset = Rez::guiX(3.0);                // 3mm per mm of font size => 30gunits / mm of font size
-    double fontSize = Rez::appX(font().pointSizeF());       //gui pts 4mm text * 10 scunits/mm = size 40 text but still only 4mm
-    double ty = svgMagicY + (svgMagicYoffset*fontSize)/dpmm;
-                    // 12mm (in gunits) + [3mm (in gunits) * (# of mm)]/ [dots per mm]  works out to dots?
-    QPointF svgMove(-svgMagicX/dpmm,ty);
-
-    QPaintDevice* hw = painter->device();
-    QSvgGenerator* svg = dynamic_cast<QSvgGenerator*>(hw);
-    if (svg) {
-        painter->scale(Rez::appX(dpmm),Rez::appX(dpmm));
-        painter->translate(svgMove);
-    } else {
-        painter->scale(1.0,1.0);
-    }
-
 //    painter->drawRect(boundingRect());          //good for debugging
 
     setDefaultTextColor(m_colCurrent);

src/Mod/TechDraw/Gui/QGIHighlight.cpp

@@ -84,7 +84,7 @@ void QGIHighlight::makeHighlight()
 void QGIHighlight::makeReference()
 {
     prepareGeometryChange();
-    m_refFont.setPointSize(m_refSize);
+    m_refFont.setPointSizeF(QGIView::calculateFontPointSizeF(this, m_refSize));
     m_reference->setFont(m_refFont);
     m_reference->setPlainText(QString::fromUtf8(m_refText));
     double fudge = Rez::guiX(1.0);

src/Mod/TechDraw/Gui/QGISectionLine.cpp

@@ -203,7 +203,7 @@ void QGISectionLine::makeSymbolsTrad()
     extLineStart = m_start + offset;
     extLineEnd = m_end + offset;
     prepareGeometryChange();
-    m_symFont.setPointSize(m_symSize);
+    m_symFont.setPointSizeF(QGIView::calculateFontPointSizeF(this, m_symSize));
     m_symbol1->setFont(m_symFont);
     m_symbol1->setPlainText(QString::fromUtf8(m_symbol));
     if (m_arrowDir.y < 0.0) {         //pointing down
@@ -246,7 +246,7 @@ void QGISectionLine::makeSymbolsISO()
     symPosEnd = m_end - offset;
 
     prepareGeometryChange();
-    m_symFont.setPointSize(m_symSize);
+    m_symFont.setPointSizeF(QGIView::calculateFontPointSizeF(this, m_symSize));
     m_symbol1->setFont(m_symFont);
     m_symbol1->setPlainText(QString::fromUtf8(m_symbol));
     m_symbol1->centerAt(symPosStart);

src/Mod/TechDraw/Gui/QGIView.cpp

@@ -98,7 +98,7 @@ QGIView::QGIView()
     m_pen.setColor(m_colCurrent);
 
     //Border/Label styling
-    m_font.setPointSize(getPrefFontSize());     //scene units (mm), not points
+    m_font.setPointSizeF(calculateFontPointSizeF(getPrefFontSize()));
 
     m_decorPen.setStyle(Qt::DashLine);
     m_decorPen.setWidth(0); // 0 => 1px "cosmetic pen"
@@ -430,7 +430,7 @@ void QGIView::drawCaption()
     QRectF displayArea = customChildrenBoundingRect();
     m_caption->setDefaultTextColor(m_colCurrent);
     m_font.setFamily(getPrefFont());
-    m_font.setPointSize(getPrefFontSize());     //scene units (0.1 mm), not points
+    m_font.setPointSizeF(calculateFontPointSizeF(getPrefFontSize()));
     m_caption->setFont(m_font);
     QString captionStr = QString::fromUtf8(getViewObject()->Caption.getValue());
     m_caption->setPlainText(captionStr);
@@ -473,7 +473,8 @@ void QGIView::drawBorder()
 
     m_label->setDefaultTextColor(m_colCurrent);
     m_font.setFamily(getPrefFont());
-    m_font.setPointSize(getPrefFontSize());     //scene units (0.1 mm), not points
+    m_font.setPointSizeF(calculateFontPointSizeF(getPrefFontSize()));
+
     m_label->setFont(m_font);
     QString labelStr = QString::fromUtf8(getViewObject()->Label.getValue());
     m_label->setPlainText(labelStr);
@@ -608,21 +609,10 @@ QGVPage* QGIView::getGraphicsView(TechDraw::DrawView* dv)
     }
     return graphicsView;
 }
+
 MDIViewPage* QGIView::getMDIViewPage(void) const
 {
-    MDIViewPage* result = nullptr;
-    QGraphicsScene* s = scene();
-    QObject* parent = nullptr;
-    if (s != nullptr) {
-        parent = s->parent();
-    }
-    if (parent != nullptr) {
-        MDIViewPage* mdi = dynamic_cast<MDIViewPage*>(parent);
-        if (mdi != nullptr) {
-            result = mdi;
-        }
-    }
-    return result;
+    return MDIViewPage::getFromScene(scene());
 }
 
 bool QGIView::getFrameState(void)
@@ -690,10 +680,37 @@ double QGIView::getPrefFontSize()
 {
     Base::Reference<ParameterGrp> hGrp = App::GetApplication().GetUserParameter().
                                          GetGroup("BaseApp")->GetGroup("Preferences")->GetGroup("Mod/TechDraw/Labels");
-    double fontSize = hGrp->GetFloat("LabelSize", 3.5);
-    return Rez::guiX(fontSize);
+    return hGrp->GetFloat("LabelSize", DefaultFontSizeInMM);
+}
+
+double QGIView::calculateFontPointSizeF(const QGraphicsItem *item, double sizeInMillimetres)
+{
+    const QWidget *widget = MDIViewPage::getFromScene(item->scene());
+    if (widget == nullptr && !QApplication::topLevelWidgets().isEmpty()) {
+        // Fallback to some top level window if we are not assigned to a scene/widget yet
+        widget = QApplication::topLevelWidgets().first();
+    }
+
+    double logicalDPI = 96.0; // This is the most common value in PC world
+    if (widget != nullptr) {
+        logicalDPI = widget->logicalDpiY();
+    }
+
+    // Now calculate the correct font size to be used by a QGraphicsTextItem:
+    // 1) Start with font size in mm.
+    // 2) Convert it to "pixels" via Rex::GuiX().
+    // 3) Convert "pixels" to inches dividing them by DPI.
+    // 4) Convert inches to points - there are exactly 72 points to one inch.
+    return 72.0*Rez::guiX(sizeInMillimetres)/logicalDPI;
 }
 
+double QGIView::calculateFontPointSizeF(double sizeInMillimetres) const
+{
+    return calculateFontPointSizeF(this, sizeInMillimetres);
+}
+
+const double QGIView::DefaultFontSizeInMM = 5.0;
+
 void QGIView::dumpRect(char* text, QRectF r) {
     Base::Console().Message("DUMP - %s - rect: (%.3f,%.3f) x (%.3f,%.3f)\n",text,
                             r.left(),r.top(),r.right(),r.bottom());

src/Mod/TechDraw/Gui/QGIView.h

@@ -111,7 +111,11 @@ class TechDrawGuiExport  QGIView : public QObject, public QGraphicsItemGroup
 
     static Gui::ViewProvider* getViewProvider(App::DocumentObject* obj);
     static QGVPage* getGraphicsView(TechDraw::DrawView* dv);
+    static double calculateFontPointSizeF(const QGraphicsItem *graphicsItem, double sizeInMillimetres);
+    static const double DefaultFontSizeInMM;
+
     MDIViewPage* getMDIViewPage(void) const;
+
     // Mouse handling
     virtual void mousePressEvent(QGraphicsSceneMouseEvent *event) override;
     boost::signals2::signal<void (QGIView*, QPointF)> signalSelectPoint;
@@ -133,6 +137,8 @@ public Q_SLOTS:
 
     QString getPrefFont(void);
     double getPrefFontSize(void);
+    double calculateFontPointSizeF(double sizeInMillimetres) const;
+
     Base::Reference<ParameterGrp> getParmGroupCol(void);
 
     TechDraw::DrawView *viewObj;

src/Mod/TechDraw/Gui/QGIViewBalloon.cpp

@@ -181,7 +181,7 @@ void QGIViewBalloon::placeBalloon(QPointF pos)
         balloon->Text.setValue(std::to_string(idx).c_str());
 
         QFont font = balloonLabel->getFont();
-        font.setPointSizeF(Rez::guiX(vp->Fontsize.getValue()));
+        font.setPointSizeF(calculateFontPointSizeF(vp->Fontsize.getValue()));
         font.setFamily(QString::fromUtf8(vp->Font.getValue()));
         balloonLabel->setFont(font);
         prepareGeometryChange();
@@ -263,7 +263,7 @@ void QGIViewBalloon::updateBalloon(bool obtuse)
     }
 
     QFont font = balloonLabel->getFont();
-    font.setPointSizeF(Rez::guiX(vp->Fontsize.getValue()));
+    font.setPointSizeF(calculateFontPointSizeF(vp->Fontsize.getValue()));
     font.setFamily(QString::fromUtf8(vp->Font.getValue()));
     balloonLabel->setFont(font);
 

src/Mod/TechDraw/Gui/QGIViewDimension.cpp

@@ -402,10 +402,6 @@ void QGIViewDimension::updateView(bool update)
      }
      else if(vp->Fontsize.isTouched() ||
                vp->Font.isTouched()) {
-         QFont font = datumLabel->getFont();
-         font.setPointSizeF(Rez::guiX(vp->Fontsize.getValue()));
-         font.setFamily(QString::fromLatin1(vp->Font.getValue()));
-         datumLabel->setFont(font);
          updateDim();
     } else if (vp->LineWidth.isTouched()) {           //never happens!!
         m_lineWidth = vp->LineWidth.getValue();
@@ -432,10 +428,10 @@ void QGIViewDimension::updateDim(bool obtuse)
     QString labelText = QString::fromUtf8(dim->getFormatedValue(m_obtuse).c_str());
 
     QFont font = datumLabel->getFont();
-    font.setPointSizeF(Rez::guiX(vp->Fontsize.getValue()));
     font.setFamily(QString::fromUtf8(vp->Font.getValue()));
-
+    font.setPointSizeF(calculateFontPointSizeF(this, vp->Fontsize.getValue()));
     datumLabel->setFont(font);
+
     prepareGeometryChange();
     datumLabel->setDimString(labelText);
     datumLabel->setTolString();

src/Mod/TechDraw/Gui/QGVPage.cpp

@@ -96,6 +96,7 @@
 #include "ZVALUE.h"
 #include "ViewProviderPage.h"
 #include "QGVPage.h"
+#include "MDIViewPage.h"
 
 using namespace Gui;
 using namespace TechDraw;
@@ -746,7 +747,9 @@ void QGVPage::saveSvg(QString filename)
     // the width and height attributes of the <svg> element."  >> but Inkscape won't read it without size info??
     svgGen.setViewBox(QRect(0, 0, Rez::guiX(page->getPageWidth()), Rez::guiX(page->getPageHeight())));
 
-    svgGen.setResolution(Rez::guiX(25.4));    // docs say this is DPI. Rez::guiX(1dot/mm) so 254 dpi?
+    // Set resolution in DPI. To keep text dimensions as they are on screen,
+    // use the very same resolution the screen paint device reports.
+    svgGen.setResolution(MDIViewPage::getFromScene(scene())->logicalDpiY());
 
     svgGen.setTitle(QObject::tr("FreeCAD SVG Export"));
     svgGen.setDescription(svgDescription);

src/Mod/TechDraw/Gui/ViewProviderBalloon.cpp

@@ -70,7 +70,7 @@ ViewProviderBalloon::ViewProviderBalloon()
 
     hGrp = App::GetApplication().GetUserParameter()
                                          .GetGroup("BaseApp")->GetGroup("Preferences")->GetGroup("Mod/TechDraw/Dimensions");
-    double fontSize = hGrp->GetFloat("FontSize", 3.5);
+    double fontSize = hGrp->GetFloat("FontSize", QGIView::DefaultFontSizeInMM);
     ADD_PROPERTY_TYPE(Font ,(fontName.c_str()),group,App::Prop_None, "The name of the font to use");
     ADD_PROPERTY_TYPE(Fontsize,(fontSize)    ,group,(App::PropertyType)(App::Prop_None),"Dimension text size in units");
 

src/Mod/TechDraw/Gui/ViewProviderDimension.cpp

@@ -60,7 +60,7 @@ ViewProviderDimension::ViewProviderDimension()
 
     hGrp = App::GetApplication().GetUserParameter()
                                          .GetGroup("BaseApp")->GetGroup("Preferences")->GetGroup("Mod/TechDraw/Dimensions");
-    double fontSize = hGrp->GetFloat("FontSize", 3.5);
+    double fontSize = hGrp->GetFloat("FontSize", QGIView::DefaultFontSizeInMM);
     ADD_PROPERTY_TYPE(Font ,(fontName.c_str()),group,App::Prop_None, "The name of the font to use");
     ADD_PROPERTY_TYPE(Fontsize,(fontSize)    ,group,(App::PropertyType)(App::Prop_None),"Dimension text size in units");