From 8884c4044d7c1d29526aca7b0be1734231c89207 Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Mon, 18 Jul 2016 16:44:06 +0200
Subject: [PATCH] Add feedback in status bar when zooming

Moreover enforce better the lower limit of 10 and avoid overflow due
to unsigned int.

Fixes bug #10212.
---
 src/LyXRC.cpp                 |  2 ++
 src/frontends/qt4/GuiView.cpp | 20 ++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/LyXRC.cpp b/src/LyXRC.cpp
index 8b7c3b3ec8..7696d0991f 100644
--- a/src/LyXRC.cpp
+++ b/src/LyXRC.cpp
@@ -604,6 +604,8 @@ LyXRC::ReturnValues LyXRC::read(Lexer & lexrc, bool check_format)
 
 		case RC_SCREEN_ZOOM:
 			lexrc >> zoom;
+			if (zoom < 10)
+				zoom = 10;
 			break;
 
 		case RC_GEOMETRY_SESSION:
diff --git a/src/frontends/qt4/GuiView.cpp b/src/frontends/qt4/GuiView.cpp
index b94625b7ca..1342eb7998 100644
--- a/src/frontends/qt4/GuiView.cpp
+++ b/src/frontends/qt4/GuiView.cpp
@@ -1990,6 +1990,8 @@ bool GuiView::getStatus(FuncRequest const & cmd, FuncStatus & flag)
 
 	case LFUN_BUFFER_ZOOM_OUT:
 		enable = doc_buffer && lyxrc.zoom > 10;
+		if (lyxrc.zoom <= 10)
+			flag.message(_("Zoom level cannot be less than 10%."));
 		break;
 
 	case LFUN_BUFFER_ZOOM_IN:
@@ -3933,17 +3935,22 @@ void GuiView::dispatch(FuncRequest const & cmd, DispatchResult & dr)
 			break;
 
 		case LFUN_BUFFER_ZOOM_IN:
-		case LFUN_BUFFER_ZOOM_OUT:
+		case LFUN_BUFFER_ZOOM_OUT: {
+			// use a signed temp to avoid overflow
+			int zoom = lyxrc.zoom;
 			if (cmd.argument().empty()) {
 				if (cmd.action() == LFUN_BUFFER_ZOOM_IN)
-					lyxrc.zoom += 20;
+					zoom += 20;
 				else
-					lyxrc.zoom -= 20;
+					zoom -= 20;
 			} else
-				lyxrc.zoom += convert<int>(cmd.argument());
+				zoom += convert<int>(cmd.argument());
 
-			if (lyxrc.zoom < 10)
-				lyxrc.zoom = 10;
+			if (zoom < 10)
+				zoom = 10;
+			lyxrc.zoom = zoom;
+
+			dr.setMessage(bformat(_("Zoom level is now %1$d%"), lyxrc.zoom));
 
 			// The global QPixmapCache is used in GuiPainter to cache text
 			// painting so we must reset it.
@@ -3951,6 +3958,7 @@ void GuiView::dispatch(FuncRequest const & cmd, DispatchResult & dr)
 			guiApp->fontLoader().update();
 			lyx::dispatch(FuncRequest(LFUN_SCREEN_FONT_UPDATE));
 			break;
+		}
 
 		case LFUN_VC_REGISTER:
 		case LFUN_VC_RENAME: