[LyX/master] Fix on-screen display of special math fonts

[Enrico Forestieri]

commit 062d94c5daeede6ee75a78491d1d26be79356192
Author: Enrico Forestieri <forenr at lyx.org>
Date:   Sun Sep 6 18:16:04 2020 +0200

    Fix on-screen display of special math fonts
    
    Make sure that the on-screen representation of the special math fonts
    mathbb, mathds, mathfrak, mathcal, and mathscr matches the latex output.
---
 src/frontends/qt/GuiFontLoader.cpp |    1 +
 src/mathed/InsetMathChar.cpp       |   14 ++++++++++++++
 src/mathed/MathSupport.cpp         |   17 ++++++++++++++---
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/frontends/qt/GuiFontLoader.cpp b/src/frontends/qt/GuiFontLoader.cpp
index c22c7f1..afbf037 100644
--- a/src/frontends/qt/GuiFontLoader.cpp
+++ b/src/frontends/qt/GuiFontLoader.cpp
@@ -215,6 +215,7 @@ QFont symbolFont(QString const & family, bool * ok)
 #else
 	font.setFamily(family);
 #endif
+	font.setStyleStrategy(QFont::NoFontMerging);
 #if QT_VERSION >= 0x040800
 	font.setStyleName("LyX");
 
diff --git a/src/mathed/InsetMathChar.cpp b/src/mathed/InsetMathChar.cpp
index d5ef8dc..aa1ddf8 100644
--- a/src/mathed/InsetMathChar.cpp
+++ b/src/mathed/InsetMathChar.cpp
@@ -118,6 +118,13 @@ void InsetMathChar::metrics(MetricsInfo & mi, Dimension & dim) const
 		Changer dummy = mi.base.font.changeShape(UP_SHAPE);
 		dim = theFontMetrics(mi.base.font).dimension(char_);
 		kerning_ = 0;
+	} else if (!isASCII(char_) && Encodings::unicodeCharInfo(char_).isUnicodeSymbol()) {
+		Changer dummy1 = mi.base.changeFontSet("mathnormal");
+		Changer dummy2 = Encodings::isMathAlpha(char_)
+				? Changer()
+				: mi.base.font.changeShape(UP_SHAPE);
+		dim = theFontMetrics(mi.base.font).dimension(char_);
+		kerning_ = -mathed_char_kerning(mi.base.font, char_);
 	} else {
 		frontend::FontMetrics const & fm = theFontMetrics(mi.base.font);
 		dim = fm.dimension(char_);
@@ -156,6 +163,13 @@ void InsetMathChar::draw(PainterInfo & pi, int x, int y) const
 			Changer dummy = pi.base.font.changeShape(UP_SHAPE);
 			pi.draw(x, y, char_);
 			return;
+		} else if (!isASCII(char_) && Encodings::unicodeCharInfo(char_).isUnicodeSymbol()) {
+			Changer dummy1 = pi.base.changeFontSet("mathnormal");
+			Changer dummy2 = Encodings::isMathAlpha(char_)
+					? Changer()
+					: pi.base.font.changeShape(UP_SHAPE);
+			pi.draw(x, y, char_);
+			return;
 		}
 	}
 	// cmmi has almost no left bearing: simulate this
diff --git a/src/mathed/MathSupport.cpp b/src/mathed/MathSupport.cpp
index ef93cb0..f5278b1 100644
--- a/src/mathed/MathSupport.cpp
+++ b/src/mathed/MathSupport.cpp
@@ -692,7 +692,13 @@ int mathedSymbolDim(MetricsBase & mb, Dimension & dim, latexkeys const * sym)
 		sym->extra == "mathalpha" &&
 		mb.fontname == "mathit";
 	std::string const font = italic_upcase_greek ? "cmm" : sym->inset;
-	Changer dummy = mb.changeFontSet(font);
+	bool const change_font = font != "cmr" ||
+				(mb.fontname != "mathbb" &&
+				 mb.fontname != "mathds" &&
+				 mb.fontname != "mathfrak" &&
+				 mb.fontname != "mathcal" &&
+				 mb.fontname != "mathscr");
+	Changer dummy = change_font ? mb.changeFontSet(font) : Changer();
 	mathed_string_dim(mb.font, mathedSymbol(mb, sym), dim);
 	return mathed_char_kerning(mb.font, mathedSymbol(mb, sym).back());
 }
@@ -710,8 +716,13 @@ void mathedSymbolDraw(PainterInfo & pi, int x, int y, latexkeys const * sym)
 		sym->extra == "mathalpha" &&
 		pi.base.fontname == "mathit";
 	std::string const font = italic_upcase_greek ? "cmm" : sym->inset;
-
-	Changer dummy = pi.base.changeFontSet(font);
+	bool const change_font = font != "cmr" ||
+				(pi.base.fontname != "mathbb" &&
+				 pi.base.fontname != "mathds" &&
+				 pi.base.fontname != "mathfrak" &&
+				 pi.base.fontname != "mathcal" &&
+				 pi.base.fontname != "mathscr");
+	Changer dummy = change_font ? pi.base.changeFontSet(font) : Changer();
 	pi.draw(x, y, mathedSymbol(pi.base, sym));
 }