Improve support for on screen length calculation

The computation of length on screen depend in particular of the computation of the size of an em. Many places of the code used to rely on the width of the M character, which is not really correct:
http://en.wikipedia.org/wiki/Em_%28typography%29

In digital typography, the best value to use is the point size of the font.

* Implement FontMetrics::em(), which returns the value in pixels of the EM unit.
 Convert code to use it.

* Introduce Length::inPixel(MetricsBase const &), which takes the textwidth and em information from the MetricsBase object. Convert code to use it.

* Fix several places where Length::inPixel is used without a proper em value.

* add mathed_font_em() helper function. It should eventually be removed like some other functions in MathSupport.

* Add dummy implementation of FontMetrics to tex2lyx for linking purposes.

src/BufferView.cpp

@@ -3000,7 +3000,7 @@ void BufferView::checkCursorScrollOffset(PainterInfo & pi)
 
 	// Horizontal scroll offset of the cursor row in pixels
 	int offset = d->horiz_scroll_offset_;
-	int const MARGIN = Length(2, Length::EM).inPixels(workWidth());
+	int const MARGIN = Length(2, Length::EM).inPixels(pi.base);
 	if (cur_x < offset + MARGIN) {
 		// scroll right
 		offset = cur_x - MARGIN;

src/Length.cpp

@@ -17,6 +17,9 @@
 
 #include "Length.h"
 #include "LyXRC.h"
+#include "MetricsInfo.h"
+
+#include "frontends/FontMetrics.h"
 
 #include "support/docstream.h"
 
@@ -197,7 +200,7 @@ int Length::inPixels(int text_width, int em_width_base) const
 		? em_width_base
 		: 10*(dpi/72.27)*zoom;
 	// A different estimate for em_width is
-	// theFontMetrics(FontInfo(sane_font)).width('M')
+	// theFontMetrics(FontInfo(sane_font)).em()
 	// but this estimate might not be more accurate as the screen font
 	// is different then the latex font.
 
@@ -288,6 +291,12 @@ int Length::inPixels(int text_width, int em_width_base) const
 }
 
 
+int Length::inPixels(MetricsBase const & base) const
+{
+	return inPixels(base.textwidth, theFontMetrics(base.font).em());
+}
+
+
 int Length::inBP() const
 {
 	// return any Length value as a one with

src/Length.h

@@ -20,6 +20,8 @@
 
 namespace lyx {
 
+class MetricsBase;
+
 // Solaris/x86 version 9 and earlier define these
 #undef PC
 #undef SP
@@ -87,8 +89,18 @@ public:
 	std::string const asLatexString() const;
 	/// return string representation for HTML
 	std::string const asHTMLString() const;
-	/// return the on-screen size of this length
+	/** return the on-screen size of this length.
+	 *
+	 *	If the second argument is not provided, then the unit EM will
+	 *	only be approximated. It is better if possible to use
+	 *	FontMetrics::em() to get this value.
+	 */
 	int inPixels(int text_width, int em_width = 0) const;
+	/** return the on-screen size of this length
+	 *
+	 *  This version of the function uses the right EM definition.
+	 */
+	int inPixels(MetricsBase const &) const;
 	/// return the value in Big Postscript points.
 	int inBP() const;
 

src/TextMetrics.cpp

@@ -1736,7 +1736,7 @@ int TextMetrics::leftMargin(int max_width,
 	}
 
 	if (!par.params().leftIndent().zero())
-		l_margin += par.params().leftIndent().inPixels(max_width);
+		l_margin += par.params().leftIndent().inPixels(max_width, labelfont_metrics.em());
 
 	LyXAlignment align;
 

src/frontends/FontMetrics.h

@@ -63,6 +63,9 @@ public:
 	/// return default dimension of the font.
 	/// \warning \c width is set to zero.
 	virtual Dimension const defaultDimension() const = 0;
+	/// return the em size
+	virtual int em() const = 0;
+
 	/// return the width of the char in the font
 	virtual int width(char_type c) const = 0;
 	/// return the ascent of the char in the font

src/frontends/qt4/GuiFontMetrics.cpp

@@ -72,6 +72,12 @@ int GuiFontMetrics::maxDescent() const
 }
 
 
+int GuiFontMetrics::em() const
+{
+	return QFontInfo(font_).pixelSize();
+}
+
+
 int GuiFontMetrics::lbearing(char_type c) const
 {
 	if (!is_utf16(c))

src/frontends/qt4/GuiFontMetrics.h

@@ -35,6 +35,7 @@ public:
 	virtual int maxAscent() const;
 	virtual int maxDescent() const;
 	virtual Dimension const defaultDimension() const;
+	virtual int em() const;
 	virtual int width(char_type c) const;
 	virtual int ascent(char_type c) const;
 	virtual int descent(char_type c) const;

src/insets/InsetBox.cpp

@@ -171,7 +171,7 @@ void InsetBox::metrics(MetricsInfo & m, Dimension & dim) const
 	// back up textwidth.
 	int textwidth_backup = m.base.textwidth;
 	if (hasFixedWidth())
-		m.base.textwidth = params_.width.inPixels(m.base.textwidth);
+		m.base.textwidth = params_.width.inPixels(m.base);
 	InsetCollapsable::metrics(m, dim);
 	// retore textwidth.
 	m.base.textwidth = textwidth_backup;

src/insets/InsetLine.cpp

@@ -111,7 +111,7 @@ void InsetLine::metrics(MetricsInfo & mi, Dimension & dim) const
 	int const max_width = mi.base.textwidth;
 
 	Length const width(to_ascii(getParam("width")));
-	dim.wid = width.inPixels(max_width, fm.width(char_type('M')));
+	dim.wid = width.inPixels(mi.base);
 
 	// assure that the line inset is not outside of the window
 	// check that it doesn't exceed the outer boundary
@@ -123,11 +123,11 @@ void InsetLine::metrics(MetricsInfo & mi, Dimension & dim) const
 	dim.wid = max(minw, abs(dim.wid));
 
 	Length height = Length(to_ascii(getParam("height")));
-	height_ = height.inPixels(max_width, fm.width(char_type('M')));
+	height_ = height.inPixels(mi.base);
 
 	// get the length of the parameters in pixels
 	Length offset = Length(to_ascii(getParam("offset")));
-	offset_ = offset.inPixels(max_width, fm.width(char_type('M')));
+	offset_ = offset.inPixels(mi.base);
 
 	dim.asc = max(fm.maxAscent(), offset_ + height_);
 	dim.des = max(fm.maxDescent(), - offset_);

src/insets/InsetSpace.cpp

@@ -209,19 +209,20 @@ void InsetSpace::metrics(MetricsInfo & mi, Dimension & dim) const
 	frontend::FontMetrics const & fm = theFontMetrics(mi.base.font);
 	dim.asc = fm.maxAscent();
 	dim.des = fm.maxDescent();
+	int const em = fm.em();
 
 	switch (params_.kind) {
 		case InsetSpaceParams::THIN:
 		case InsetSpaceParams::NEGTHIN:
-			dim.wid = fm.width(char_type('M')) / 6;
+			dim.wid = em / 6;
 			break;
 		case InsetSpaceParams::MEDIUM:
 		case InsetSpaceParams::NEGMEDIUM:
-			dim.wid = fm.width(char_type('M')) / 4;
+			dim.wid = em / 4;
 			break;
 		case InsetSpaceParams::THICK:
 		case InsetSpaceParams::NEGTHICK:
-			dim.wid = fm.width(char_type('M')) / 2;
+			dim.wid = em / 2;
 			break;
 		case InsetSpaceParams::PROTECTED:
 		case InsetSpaceParams::VISIBLE:
@@ -229,20 +230,19 @@ void InsetSpace::metrics(MetricsInfo & mi, Dimension & dim) const
 			dim.wid = fm.width(char_type(' '));
 			break;
 		case InsetSpaceParams::QUAD:
-			dim.wid = fm.width(char_type('M'));
+			dim.wid = em;
 			break;
 		case InsetSpaceParams::QQUAD:
-			dim.wid = 2 * fm.width(char_type('M'));
+			dim.wid = 2 * em;
 			break;
 		case InsetSpaceParams::ENSPACE:
 		case InsetSpaceParams::ENSKIP:
-			dim.wid = int(0.5 * fm.width(char_type('M')));
+			dim.wid = int(0.5 * em);
 			break;
 		case InsetSpaceParams::CUSTOM:
 		case InsetSpaceParams::CUSTOM_PROTECTED: {
 			int const w =
-				params_.length.len().inPixels(mi.base.textwidth,
-							fm.width(char_type('M')));
+				params_.length.len().inPixels(mi.base);
 			int const minw = (w < 0) ? 3 * arrow_size : 4;
 			dim.wid = max(minw, abs(w));
 			break;

src/insets/InsetSpecialChar.cpp

@@ -47,7 +47,7 @@ namespace {
 
 int logoWidth(FontInfo const & font, InsetSpecialChar::Kind kind) {
 	frontend::FontMetrics const & fm = theFontMetrics(font);
-	int const em = fm.width('M');
+	int const em = fm.em();
 	int width = 0;
 	// See drawlogo() below to understand what this does.
 	switch (kind) {
@@ -137,9 +137,7 @@ namespace {
 
 void drawLogo(PainterInfo & pi, InsetSpecialChar::Kind kind, int & x, int & y) {
 	FontInfo const & font = pi.base.font;
-	// FIXME: this definition of em is bogus, but there is a need
-	// for a big refactoring of the code around this issue anyway.
-	int const em = theFontMetrics(font).width('M');
+	int const em = theFontMetrics(font).em();
 	switch (kind) {
 	case InsetSpecialChar::PHRASE_LYX:
 		/** Reference macro:

src/insets/InsetTabular.cpp

@@ -3591,7 +3591,7 @@ void InsetTabular::metrics(MetricsInfo & mi, Dimension & dim) const
 			MetricsInfo m = mi;
 			Length const p_width = tabular.getPWidth(cell);
 			if (!p_width.zero())
-				m.base.textwidth = p_width.inPixels(mi.base.textwidth);
+				m.base.textwidth = p_width.inPixels(mi.base);
 			tabular.cellInset(cell)->metrics(m, dim);
 			if (!p_width.zero())
 				dim.wid = m.base.textwidth;
@@ -3652,11 +3652,11 @@ void InsetTabular::metrics(MetricsInfo & mi, Dimension & dim) const
 		}
 		int const top_space = tabular.row_info[r].top_space_default ?
 			default_line_space :
-			tabular.row_info[r].top_space.inPixels(mi.base.textwidth);
+			tabular.row_info[r].top_space.inPixels(mi.base);
 		tabular.setRowAscent(r, maxasc + ADD_TO_HEIGHT + top_space);
 		int const bottom_space = tabular.row_info[r].bottom_space_default ?
 			default_line_space :
-			tabular.row_info[r].bottom_space.inPixels(mi.base.textwidth);
+			tabular.row_info[r].bottom_space.inPixels(mi.base);
 		tabular.setRowDescent(r, maxdes + ADD_TO_HEIGHT + bottom_space);
 	}
 

src/mathed/InsetMathChar.cpp

@@ -75,7 +75,7 @@ void InsetMathChar::metrics(MetricsInfo & mi, Dimension & dim) const
 		dim = fm.dimension(char_);
 		kerning_ = fm.rbearing(char_) - dim.wid;
 	}
-	int const em = mathed_char_width(mi.base.font, 'M');
+	int const em = mathed_font_em(mi.base.font);
 	if (isBinaryOp(char_))
 		dim.wid += static_cast<int>(0.5*em+0.5);
 	else if (char_ == '\'')
@@ -93,7 +93,7 @@ void InsetMathChar::metrics(MetricsInfo & mi, Dimension & dim) const
 void InsetMathChar::draw(PainterInfo & pi, int x, int y) const
 {
 	//lyxerr << "drawing '" << char_ << "' font: " << pi.base.fontname << endl;
-	int const em = mathed_char_width(pi.base.font, 'M');
+	int const em = mathed_font_em(pi.base.font);
 	if (isBinaryOp(char_))
 		x += static_cast<int>(0.25*em+0.5);
 	else if (char_ == '\'')

src/mathed/InsetMathGrid.cpp

@@ -28,7 +28,6 @@
 #include "FuncRequest.h"
 
 #include "frontends/Clipboard.h"
-#include "frontends/FontMetrics.h"
 #include "frontends/Painter.h"
 
 #include "support/debug.h"
@@ -98,9 +97,7 @@ InsetMathGrid::RowInfo::RowInfo()
 
 int InsetMathGrid::RowInfo::skipPixels(MetricsInfo const & mi) const
 {
-	frontend::FontMetrics const & fm = theFontMetrics(mi.base.font);
-	return crskip_.inPixels(mi.base.textwidth,
-				fm.width(char_type('M')));
+	return crskip_.inPixels(mi.base);
 }
 
 

src/mathed/InsetMathKern.cpp

@@ -47,7 +47,7 @@ void InsetMathKern::metrics(MetricsInfo & mi, Dimension & dim) const
 {
 	dim.asc = 0;
 	dim.des = 0;
-	dim.wid = wid_.inPixels(0, mathed_char_width(mi.base.font, 'M'));
+	dim.wid = wid_.inPixels(mi.base);
 }
 
 

src/mathed/InsetMathSpace.cpp

@@ -123,9 +123,7 @@ void InsetMathSpace::metrics(MetricsInfo & mi, Dimension & dim) const
 	dim.asc = 4;
 	dim.des = 0;
 	if (space_info[space_].custom)
-		dim.wid = abs(length_.inPixels(
-				mi.base.textwidth,
-				mathed_char_width(mi.base.font, 'M')));
+		dim.wid = abs(length_.inPixels(mi.base));
 	else
 		dim.wid = space_info[space_].width;
 }

src/mathed/InsetMathSymbol.cpp

@@ -67,7 +67,7 @@ void InsetMathSymbol::metrics(MetricsInfo & mi, Dimension & dim) const
 					 sym_->extra == "mathalpha" &&
 					 mi.base.fontname == "mathit";
 	std::string const font = italic_upcase_greek ? "cmm" : sym_->inset;
-	int const em = mathed_char_width(mi.base.font, 'M');
+	int const em = mathed_font_em(mi.base.font);
 	FontSetChanger dummy(mi.base, from_ascii(font));
 	mathed_string_dim(mi.base.font, sym_->draw, dim);
 	docstring::const_reverse_iterator rit = sym_->draw.rbegin();
@@ -104,7 +104,7 @@ void InsetMathSymbol::draw(PainterInfo & pi, int x, int y) const
 					 sym_->extra == "mathalpha" &&
 					 pi.base.fontname == "mathit";
 	std::string const font = italic_upcase_greek ? "cmm" : sym_->inset;
-	int const em = mathed_char_width(pi.base.font, 'M');
+	int const em = mathed_font_em(pi.base.font);
 	if (isRelOp())
 		x += static_cast<int>(0.25*em+0.5);
 	else

src/mathed/MathSupport.cpp

@@ -501,6 +501,12 @@ deco_struct const * search_deco(docstring const & name)
 } // namespace anon
 
 
+int mathed_font_em(FontInfo const & font)
+{
+	return theFontMetrics(font).em();
+}
+
+
 int mathed_char_width(FontInfo const & font, char_type c)
 {
 	return theFontMetrics(font).width(c);

src/mathed/MathSupport.h

@@ -27,6 +27,8 @@ class MathAtom;
 class InsetMath;
 
 
+int mathed_font_em(FontInfo const &);
+
 int mathed_char_width(FontInfo const &, char_type c);
 
 int mathed_char_kerning(FontInfo const &, char_type c);

src/tex2lyx/dummy_impl.cpp

@@ -121,6 +121,22 @@ string alignmentToCSS(LyXAlignment)
 	return string();
 }
 
+//
+// Dummy FontMetrics (needed by Length)
+//
+
+
+class FontMetrics {
+	int em() const { return 0; };
+};
+
+class FontInfo;
+
+FontMetrics const & theFontMetrics(FontInfo const &) {
+	static FontMetrics dummy;
+	return dummy;
+}
+
 //
 // Keep the linker happy on Windows
 //