Do not draw inactive math corners when they have mathbg color

By default, inactive math corners are invisible. In practice they are
annoying because they are visible when selecting text, and they can
also overwrite some parts of the equation.

The code in Inset::drawMarkers2, which is only used for maths, is
moved to InsetMathHull. Moreover, the inactive corners are not drawn
when they have the same color as the math background. A better way to
achieve this would be to set the color to transparent, but we do not
support this yet.

(cherry picked from commit 68614e9783)

src/insets/Inset.cpp

@@ -553,22 +553,6 @@ void Inset::drawMarkers(PainterInfo & pi, int x, int y) const
 }
 
 
-void Inset::drawMarkers2(PainterInfo & pi, int x, int y) const
-{
-	ColorCode pen_color = mouseHovered(pi.base.bv) || editing(pi.base.bv)?
-		Color_mathframe : Color_mathcorners;
-
-	drawMarkers(pi, x, y);
-	Dimension const dim = dimension(*pi.base.bv);
-	int const t = x + dim.width() - 1;
-	int const a = y - dim.ascent();
-	pi.pain.line(x, a + 3, x, a, pen_color);
-	pi.pain.line(t, a + 3, t, a, pen_color);
-	pi.pain.line(x, a, x + 3, a, pen_color);
-	pi.pain.line(t - 3, a, t, a, pen_color);
-}
-
-
 bool Inset::editing(BufferView const * bv) const
 {
 	return bv->cursor().isInside(this);

src/insets/Inset.h

@@ -210,9 +210,7 @@ public:
 	virtual bool showInsetDialog(BufferView *) const;
 
 	/// draw two angular markers
-	void drawMarkers(PainterInfo & pi, int x, int y) const;
+	virtual void drawMarkers(PainterInfo & pi, int x, int y) const;
-	/// draw four angular markers
-	void drawMarkers2(PainterInfo & pi, int x, int y) const;
 	/// add space for markers
 	void metricsMarkers(Dimension & dim, int framesize = 1) const;
 	/// add space for markers

src/mathed/InsetMathHull.cpp

@@ -599,6 +599,25 @@ ColorCode InsetMathHull::backgroundColor(PainterInfo const & pi) const
 }
 
 
+void InsetMathHull::drawMarkers(PainterInfo & pi, int x, int y) const
+{
+	ColorCode pen_color = mouseHovered(pi.base.bv) || editing(pi.base.bv)?
+		Color_mathframe : Color_mathcorners;
+	// If the corners have the same color as the background, do not paint them.
+	if (lcolor.getX11Name(Color_mathbg) == lcolor.getX11Name(pen_color))
+		return;
+
+	Inset::drawMarkers(pi, x, y);
+	Dimension const dim = dimension(*pi.base.bv);
+	int const t = x + dim.width() - 1;
+	int const a = y - dim.ascent();
+	pi.pain.line(x, a + 3, x, a, pen_color);
+	pi.pain.line(t, a + 3, t, a, pen_color);
+	pi.pain.line(x, a, x + 3, a, pen_color);
+	pi.pain.line(t - 3, a, t, a, pen_color);
+}
+
+
 void InsetMathHull::drawBackground(PainterInfo & pi, int x, int y) const
 {
 	Dimension const dim = dimension(*pi.base.bv);
@@ -659,7 +678,7 @@ void InsetMathHull::draw(PainterInfo & pi, int x, int y) const
 	}
 
 	InsetMathGrid::draw(pi, xmath + 1, y);
-	drawMarkers2(pi, x, y);
+	drawMarkers(pi, x, y);
 
 	if (numberedType()) {
 		Changer dummy = pi.base.changeFontSet("mathrm");

src/mathed/InsetMathHull.h

@@ -260,6 +260,8 @@ private:
 	bool colChangeOK() const;
 	/// are any of the equations numbered?
 	bool haveNumbers() const;
+	/// draw four angular markers
+	virtual void drawMarkers(PainterInfo & pi, int x, int y) const;
 
 	/// "none", "simple", "display", "eqnarray",...
 	HullType type_;

src/mathed/MathRow.cpp

@@ -18,6 +18,7 @@
 #include "MathSupport.h"
 
 #include "BufferView.h"
+#include "ColorSet.h"
 #include "CoordCache.h"
 #include "MetricsInfo.h"
 
@@ -97,11 +98,6 @@ void drawMarkers(PainterInfo const & pi, MathRow::Element const & e,
 	if (e.marker == InsetMath::NO_MARKER)
 		return;
 
-	// The color
-	bool const highlight = e.inset->mouseHovered(pi.base.bv)
-	                       || e.inset->editing(pi.base.bv);
-	ColorCode const pen_color = highlight ? Color_mathframe : Color_mathcorners;
-
 	CoordCache const & coords = pi.base.bv->coordCache();
 	Dimension const dim = coords.getInsets().dim(e.inset);
 
@@ -122,6 +118,14 @@ void drawMarkers(PainterInfo const & pi, MathRow::Element const & e,
 		pi.pain.text(l, y + dim.des - namedim.des - 1, e.inset->name(), font);
 	}
 
+	// Color for corners
+	bool const highlight = e.inset->mouseHovered(pi.base.bv)
+	                       || e.inset->editing(pi.base.bv);
+	ColorCode const pen_color = highlight ? Color_mathframe : Color_mathcorners;
+	// If the corners have the same color as the background, do not paint them.
+	if (lcolor.getX11Name(Color_mathbg) == lcolor.getX11Name(pen_color))
+		return;
+
 	// Lower corners in all cases
 	int const d = y + dim.descent();
 	pi.pain.line(l, d - 3, l, d, pen_color);