Make the session zoom relative to the default zoom

Also rename lyxrc.zoom to lyxrc.defaultZoom

Fixes: #10455

src/LyXAction.cpp

@@ -892,7 +892,8 @@ void LyXAction::init()
 * \var lyx::FuncCode lyx::LFUN_BUFFER_ZOOM
 * \li Action: Sets the zoom of the screen fonts.
 * \li Syntax: buffer-zoom [<ZOOM>]
-* \li Params: <ZOOM>: The zoom in % points (neg. or pos.), the default is to reset to zoom savd in preferences.
+* \li Params: <ZOOM>: The target zoom value in %;
+*                     the default is the default zoom as saved in preferences.
 * \li Origin: daniel, 28 Oct 2016
 * \endvar
 */
@@ -902,7 +903,8 @@ void LyXAction::init()
  * \var lyx::FuncCode lyx::LFUN_BUFFER_ZOOM_IN
  * \li Action: Increases the zoom of the screen fonts.
  * \li Syntax: buffer-zoom-in [<ZOOM>]
- * \li Params: <ZOOM>: The zoom in % points (neg. or pos.), the default is 20.
+ * \li Params: <ZOOM>: The zoom value addition in % (neg. or pos.);
+ *                     the default is 10% of the default zoom as saved in preferences.
  * \li Origin: vfr, 30 Mar 2009
  * \endvar
  */
@@ -913,7 +915,8 @@ void LyXAction::init()
  * \var lyx::FuncCode lyx::LFUN_BUFFER_ZOOM_OUT
  * \li Action: Decreases the zoom of the screen fonts.
  * \li Syntax: buffer-zoom-out [<ZOOM>]
- * \li Params: <ZOOM>: The zoom in % points (neg. or pos.), the default is -20.
+ * \li Params: <ZOOM>: The zoom value abstraction in % (neg. or pos.);
+ *                     the default is 10% of the default zoom as saved in preferences.
  * \li Origin: vfr, 30 Mar 2009
  * \endvar
  */

src/LyXRC.cpp

@@ -245,8 +245,8 @@ void LyXRC::setDefaults()
 	pygmentize_command = string();
 	dpi = 75;
 	// Because a screen is typically wider than a piece of paper:
-	zoom = 150;
+	defaultZoom = 150;
-	currentZoom = zoom;
+	currentZoom = defaultZoom;
 	allow_geometry_session = true;
 	// Default LaTeX font size:
 	font_sizes[FONT_SIZE_TINY] = "5.0";
@@ -624,9 +624,9 @@ LyXRC::ReturnValues LyXRC::read(Lexer & lexrc, bool check_format)
 			break;
 
 		case RC_SCREEN_ZOOM:
-			lexrc >> zoom;
+			lexrc >> defaultZoom;
-			if (zoom < 10)
+			if (defaultZoom < 10)
-				zoom = 10;
+				defaultZoom = 10;
 			break;
 
 		case RC_GEOMETRY_SESSION:
@@ -1724,8 +1724,8 @@ void LyXRC::write(ostream & os, bool ignore_system_lyxrc, string const & name) c
 		// fall through
 	case RC_SCREEN_ZOOM:
 		if (ignore_system_lyxrc ||
-		    zoom != system_lyxrc.zoom) {
+		    defaultZoom != system_lyxrc.defaultZoom) {
-			os << "\\screen_zoom " << zoom << '\n';
+			os << "\\screen_zoom " << defaultZoom << '\n';
 		}
 		if (tag != RC_LAST)
 			break;

src/LyXRC.h

@@ -295,9 +295,10 @@ public:
 	bool allow_geometry_session;
 	/// Scrolling speed of the mouse wheel
 	double mouse_wheel_speed;
-	/// Zoom factor for screen fonts
+	/// Default zoom factor for screen fonts
-	int zoom;
+	int defaultZoom;
-	/// Current zoom factor for screen fonts
+	/// Actual zoom factor for screen fonts
+	/// (default zoom plus buffer zoom factor)
 	int currentZoom;
 	/// Screen font sizes in points for each font size
 	std::string font_sizes[10];

src/frontends/qt4/GuiPrefs.cpp

@@ -1089,7 +1089,7 @@ void PrefScreenFonts::applyRC(LyXRC & rc) const
 	parseFontName(screenTypewriterCO->currentText(),
 		rc.typewriter_font_name, rc.typewriter_font_foundry);
 
-	rc.zoom = screenZoomSB->value();
+	rc.defaultZoom = screenZoomSB->value();
 	rc.font_sizes[FONT_SIZE_TINY] = widgetToDoubleStr(screenTinyED);
 	rc.font_sizes[FONT_SIZE_SCRIPT] = widgetToDoubleStr(screenSmallestED);
 	rc.font_sizes[FONT_SIZE_FOOTNOTE] = widgetToDoubleStr(screenSmallerED);
@@ -1106,7 +1106,7 @@ void PrefScreenFonts::applyRC(LyXRC & rc) const
 		|| rc.roman_font_name != oldrc.roman_font_name
 		|| rc.sans_font_name != oldrc.sans_font_name
 		|| rc.typewriter_font_name != oldrc.typewriter_font_name
-		|| rc.zoom != oldrc.zoom) {
+		|| rc.defaultZoom != oldrc.defaultZoom) {
 		// The global QPixmapCache is used in GuiPainter to cache text
 		// painting so we must reset it in case any of the above
 		// parameter is changed.
@@ -1130,7 +1130,7 @@ void PrefScreenFonts::updateRC(LyXRC const & rc)
 	selectSans(screenSansCO->currentText());
 	selectTypewriter(screenTypewriterCO->currentText());
 
-	screenZoomSB->setValue(rc.zoom);
+	screenZoomSB->setValue(rc.defaultZoom);
 	updateScreenFontSizes(rc);
 
 	pixmapCacheCB->setChecked(rc.use_pixmap_cache);

src/frontends/qt4/GuiView.cpp

@@ -741,7 +741,7 @@ void GuiView::autoSaveThreadFinished()
 void GuiView::saveLayout() const
 {
 	QSettings settings;
-	settings.setValue("zoom", lyxrc.currentZoom);
+	settings.setValue("zoom_ratio", zoom_ratio_);
 	settings.setValue("devel_mode", devel_mode_);
 	settings.beginGroup("views");
 	settings.beginGroup(QString::number(id_));
@@ -772,7 +772,12 @@ void GuiView::saveUISettings() const
 bool GuiView::restoreLayout()
 {
 	QSettings settings;
-	lyxrc.currentZoom = settings.value("zoom", lyxrc.zoom).toInt();
+	zoom_ratio_ = settings.value("zoom_ratio", 1.0).toDouble();
+	// Actual zoom value: default zoom + fractional offset
+	int zoom = lyxrc.defaultZoom * zoom_ratio_;
+	if (zoom < static_cast<int>(zoom_min_))
+		zoom = zoom_min_;
+	lyxrc.currentZoom = zoom;
 	devel_mode_ = settings.value("devel_mode", devel_mode_).toBool();
 	settings.beginGroup("views");
 	settings.beginGroup(QString::number(id_));
@@ -4114,30 +4119,31 @@ void GuiView::dispatch(FuncRequest const & cmd, DispatchResult & dr)
 		case LFUN_BUFFER_ZOOM_IN:
 		case LFUN_BUFFER_ZOOM_OUT:
 		case LFUN_BUFFER_ZOOM: {
-			// use a signed temp to avoid overflow
-			int zoom = lyxrc.currentZoom;
 			if (cmd.argument().empty()) {
 				if (cmd.action() == LFUN_BUFFER_ZOOM)
-					zoom = lyxrc.zoom;
+					zoom_ratio_ = 1.0;
 				else if (cmd.action() == LFUN_BUFFER_ZOOM_IN)
-					zoom += 20;
+					zoom_ratio_ += 0.1;
 				else
-					zoom -= 20;
+					zoom_ratio_ -= 0.1;
 			} else {
 				if (cmd.action() == LFUN_BUFFER_ZOOM)
-					zoom = convert<int>(cmd.argument());
+					zoom_ratio_ = convert<int>(cmd.argument()) / double(lyxrc.defaultZoom);
 				else if (cmd.action() == LFUN_BUFFER_ZOOM_IN)
-					zoom += convert<int>(cmd.argument());
+					zoom_ratio_ += convert<int>(cmd.argument()) / 100.0;
 				else
-					zoom -= convert<int>(cmd.argument());
+					zoom_ratio_ -= convert<int>(cmd.argument()) / 100.0;
 			}
 
+			// Actual zoom value: default zoom + fractional extra value
+			int zoom = lyxrc.defaultZoom * zoom_ratio_;
 			if (zoom < static_cast<int>(zoom_min_))
 				zoom = zoom_min_;
 
 			lyxrc.currentZoom = zoom;
 
-			dr.setMessage(bformat(_("Zoom level is now %1$d%"), lyxrc.currentZoom));
+			dr.setMessage(bformat(_("Zoom level is now %1$d% (default value: %2$d%)"),
+					      lyxrc.currentZoom, lyxrc.defaultZoom));
 
 			// The global QPixmapCache is used in GuiPainter to cache text
 			// painting so we must reset it.

src/frontends/qt4/GuiView.h

@@ -470,6 +470,9 @@ private:
 	/// Statusbar widget that shows version control status
 	QLabel * version_control_;
 
+	/// The rate from which the actual zoom value is calculated
+	/// from the default zoom pref
+	double zoom_ratio_ = 1.0;
 	/// Minimum zoom percentage
 	static int const zoom_min_ = 10;