Fix http://bugzilla.lyx.org/show_bug.cgi?id=4972

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/branches/BRANCH_1_5_X@25407 a592a061-630c-0410-9148-cb99ea01b6c8

src/frontends/qt4/GuiWorkArea.cpp

@@ -48,6 +48,8 @@
 #include <boost/bind.hpp>
 #include <boost/current_function.hpp>
 
+#include <cmath>
+
 #ifdef Q_WS_X11
 #include <QX11Info>
 extern "C" int XEventsQueued(Display *display, int mode);
@@ -420,9 +422,24 @@ void GuiWorkArea::wheelEvent(QWheelEvent * e)
 {
 	// Wheel rotation by one notch results in a delta() of 120 (see
 	// documentation of QWheelEvent)
-	int const lines = qApp->wheelScrollLines() * e->delta() / 120;
-	verticalScrollBar()->setValue(verticalScrollBar()->value() -
-			lines *  verticalScrollBar()->singleStep());
+	int const delta = e->delta() / 120;
+	int const lines = qApp->wheelScrollLines();
+	int scroll_value;
+	// Test if the wheel mouse is set to one screen at a time.
+	int const page_step = verticalScrollBar()->pageStep();
+	if (lines > page_step)
+		scroll_value = page_step * delta;
+	else
+		scroll_value = lines * verticalScrollBar()->singleStep() * delta;
+
+	LYXERR(Debug::GUI) << "Wheel Scroll  "
+		<< " page_step = " << page_step
+		<< " line step = " << verticalScrollBar()->singleStep()
+		<< " delta = " << delta
+		<< " lines = " << lines
+		<< " scroll_value = " << scroll_value << endl;
+	// Now scroll.
+	verticalScrollBar()->setValue(verticalScrollBar()->value() - scroll_value);
 	adjustViewWithScrollBar();
 }
 

status.15x

@@ -97,6 +97,9 @@ What's new
 
 - Use appropriate font in notes and ERT insets in section headings
   (bug 2477).
+  
+- Fix wheel mouse scrolling when it is set to "One screen at a time
+  (bug 4972).
 
 - Fix shape of braces, '$', '%', '&', and '#', which where incorrectly 
   shown in italics in mathed (bug 4320).