Allow automatic text direction in Painter::text()

It is wrong to assume that direction is left-to-right when no indication exist.

Add a new enum with values LtR, RtL and Auto to be used as argument of
the private text() methods. When direction is Auto, let Qt decide how
the string shall be layed out.

Fixes bug #10169.

src/frontends/qt4/GuiPainter.cpp

@@ -335,11 +335,13 @@ void GuiPainter::text(int x, int y, char_type c, FontInfo const & f)
 
 void GuiPainter::text(int x, int y, docstring const & s, FontInfo const & f)
 {
-	text(x, y, s, f, false, 0.0, 0.0);
+	text(x, y, s, f, Auto, 0.0, 0.0);
 }
 
 
-void GuiPainter::do_drawText(int x, int y, QString str, bool rtl, FontInfo const & f, QFont ff)
+void GuiPainter::do_drawText(int x, int y, QString str,
+                             GuiPainter::Direction const dir,
+                             FontInfo const & f, QFont ff)
 {
 	setQPainterPen(computeColor(f.realColor()));
 	if (font() != ff)
@@ -352,10 +354,10 @@ void GuiPainter::do_drawText(int x, int y, QString str, bool rtl, FontInfo const
 	/* Use unicode override characters to enforce drawing direction
 	 * Source: http://www.iamcal.com/understanding-bidirectional-text/
 	 */
-	if (rtl)
+	if (dir == RtL)
 		// Right-to-left override: forces to draw text right-to-left
 		str = QChar(0x202E) + str;
-	else
+	else if (dir == LtR)
 		// Left-to-right override: forces to draw text left-to-right
 		str =  QChar(0x202D) + str;
 	drawText(x, y, str);
@@ -366,8 +368,12 @@ void GuiPainter::do_drawText(int x, int y, QString str, bool rtl, FontInfo const
 	 * Keep it here for now, in case it can be helpful
 	 */
 	//This is much stronger than setLayoutDirection.
-	int flag = rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight;
+	int flag = 0;
-	drawText(x + (rtl ? textwidth : 0), y - fm.maxAscent(), 0, 0,
+	if (dir == RtL)
+		flag = Qt::TextForceRightToLeft;
+	else if (dir == LtR)
+		flag = Qt::TextForceLeftToRight;
+	drawText(x + ((dir == RtL) ? textwidth : 0), y - fm.maxAscent(), 0, 0,
 		 flag | Qt::TextDontClip,
 		 str);
 #endif
@@ -375,7 +381,7 @@ void GuiPainter::do_drawText(int x, int y, QString str, bool rtl, FontInfo const
 
 
 void GuiPainter::text(int x, int y, docstring const & s,
-                      FontInfo const & f, bool const rtl,
+                      FontInfo const & f, Direction const dir,
                       double const wordspacing, double const tw)
 {
 	//LYXERR0("text: x=" << x << ", s=" << s);
@@ -450,7 +456,7 @@ void GuiPainter::text(int x, int y, docstring const & s,
 #endif
 			pm.fill(Qt::transparent);
 			GuiPainter p(&pm, pixelRatio());
-			p.do_drawText(-lb, mA, str, rtl, f, ff);
+			p.do_drawText(-lb, mA, str, dir, f, ff);
 			QPixmapCache::insert(key, pm);
 			//LYXERR(Debug::PAINTING, "h=" << h << "  mA=" << mA << "  mD=" << mD
 			//	<< "  w=" << w << "  lb=" << lb << "  tw=" << textwidth
@@ -464,7 +470,7 @@ void GuiPainter::text(int x, int y, docstring const & s,
 	}
 
 	// don't use the pixmap cache,
-	do_drawText(x, y, str, rtl, f, ff);
+	do_drawText(x, y, str, dir, f, ff);
 	//LYXERR(Debug::PAINTING, "draw " << string(str.toUtf8())
 	//	<< " at " << x << "," << y);
 }
@@ -473,7 +479,8 @@ void GuiPainter::text(int x, int y, docstring const & s,
 void GuiPainter::text(int x, int y, docstring const & str, Font const & f,
                       double const wordspacing, double const tw)
 {
-	text(x, y, str, f.fontInfo(), f.isVisibleRightToLeft(), wordspacing, tw);
+	text(x, y, str, f.fontInfo(), f.isVisibleRightToLeft() ? RtL : LtR,
+	     wordspacing, tw);
 }
 
 
@@ -483,13 +490,13 @@ void GuiPainter::text(int x, int y, docstring const & str, Font const & f,
 {
 	GuiFontMetrics const & fm = getFontMetrics(f.fontInfo());
 	FontInfo fi = f.fontInfo();
-	bool const rtl = f.isVisibleRightToLeft();
+	Direction const dir = f.isVisibleRightToLeft() ? RtL : LtR;
 
 	// dimensions
 	int const ascent = fm.maxAscent();
 	int const height = fm.maxAscent() + fm.maxDescent();
-	int xmin = fm.pos2x(str, from, rtl, wordspacing);
+	int xmin = fm.pos2x(str, from, dir == RtL, wordspacing);
-	int xmax = fm.pos2x(str, to, rtl, wordspacing);
+	int xmax = fm.pos2x(str, to, dir == RtL, wordspacing);
 	if (xmin > xmax)
 		swap(xmin, xmax);
 
@@ -498,7 +505,7 @@ void GuiPainter::text(int x, int y, docstring const & str, Font const & f,
 	fi.setPaintColor(other);
 	QRegion const clip(x + xmin, y - ascent, xmax - xmin, height);
 	setClipRegion(clip);
-	text(x, y, str, fi, rtl, wordspacing, tw);
+	text(x, y, str, fi, dir, wordspacing, tw);
 
 	// Then the part in normal color
 	// Note that in Qt5, it is not possible to use Qt::UniteClip,
@@ -506,7 +513,7 @@ void GuiPainter::text(int x, int y, docstring const & str, Font const & f,
 	fi.setPaintColor(orig);
 	QRegion region(viewport());
 	setClipRegion(region - clip);
-	text(x, y, str, fi, rtl, wordspacing, tw);
+	text(x, y, str, fi, dir, wordspacing, tw);
 	setClipping(false);
 }
 

src/frontends/qt4/GuiPainter.h

@@ -180,12 +180,15 @@ private:
 	void setQPainterPen(QColor const & col,
 		line_style ls = line_solid, int lw = thin_line);
 
+	// Direction for painting text
+	enum Direction { LtR, RtL, Auto };
+
 	// Helper for text() method
-	void do_drawText(int x, int y, QString str, bool rtl, FontInfo const & f, QFont ff);
+	void do_drawText(int x, int y, QString str, Direction dir, FontInfo const & f, QFont ff);
 
 	// Real text() method
 	void text(int x, int y, docstring const & s,
-              FontInfo const & f, bool const rtl,
+              FontInfo const & f, Direction const dir,
               double const wordspacing, double tw);
 
 	QColor current_color_;