added GetVisibleBegin/End() to complement/replace GetFirst/LastVisibleLine() and use them in the code to fix problems when the control is empty and GetLastVisibleLine() returns (size_t)-1 (closes bug 1176561)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@33360 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/vscroll.tex

@@ -115,12 +115,22 @@ try to make the best guess possible.
 
 Returns the index of the first currently visible line.
 
+This is same as \helpref{GetVisibleBegin}{wxvscrolledwindowgetvisiblebegin} and
+exists only for symmetry with \helpref{GetLastVisibleLine}{wxvscrolledwindowgetlastvisibleline}.
+
 
 \membersection{wxVScrolledWindow::GetLastVisibleLine}\label{wxvscrolledwindowgetlastvisibleline}
 
 \constfunc{size\_t}{GetLastVisibleLine}{\void}
 
-Returns the index of the last currently visible line.
+Returns the index of the last currently visible line. Note that this method
+returns \texttt{(size\_t)-1} (i.e. a huge positive number) if the control is
+empty so if this is possible you should use \helpref{GetVisibleEnd}{wxvscrolledwindowgetvisibleend} 
+instead.
+
+\wxheading{See also}
+
+\helpref{GetFirstVisibleLine}{wxvscrolledwindowgetfirstvisibleline}
 
 
 \membersection{wxVScrolledWindow::GetLineCount}\label{wxvscrolledwindowgetlinecount}
@@ -131,6 +141,31 @@ Get the number of lines this window contains (previously set by
 \helpref{SetLineCount()}{wxvscrolledwindowsetlinecount})
 
 
+\membersection{wxVScrolledWindow::GetVisibleBegin}\label{wxvscrolledwindowgetvisiblebegin}
+
+\constfunc{size\_t}{GetVisibleBegin}{\void}
+
+Returns the index of the first currently visible line.
+
+\wxheading{See also}
+
+\helpref{GetVisibleEnd}{wxvscrolledwindowgetvisibleend}
+
+
+\membersection{wxVScrolledWindow::GetVisibleEnd}\label{wxvscrolledwindowgetvisibleend}
+
+\constfunc{size\_t}{GetVisibleEnd}{\void}
+
+Returns the index of the first line after the currently visible one. If the
+return value is $0$ it means that no lines are currently shown (which only
+happens if the control is empty). Note that the index returned by this method
+is not always a valid index as it may be equal to \helpref{GetLineCount}{wxvscrolledwindowsetlinecount}.
+
+\wxheading{See also}
+
+\helpref{GetVisibleBegin}{wxvscrolledwindowgetvisiblebegin}
+
+
 \membersection{wxVScrolledWindow::HitTest}\label{wxvscrolledwindowhittest}
 
 \constfunc{int}{HitTest}{\param{wxCoord }{x}, \param{wxCoord }{y}}

include/wx/vscroll.h

@@ -118,14 +118,26 @@ public:
     size_t GetLineCount() const { return m_lineMax; }
 
     // get the first currently visible line
-    size_t GetFirstVisibleLine() const { return m_lineFirst; }
+    size_t GetVisibleBegin() const { return m_lineFirst; }
 
-    // get the last currently visible line
-    size_t GetLastVisibleLine() const { return m_lineFirst + m_nVisible - 1; }
+    // get the first currently visible line
+    size_t GetVisibleEnd() const { return m_lineFirst + m_nVisible; }
 
     // is this line currently visible?
     bool IsVisible(size_t line) const
-        { return line >= m_lineFirst && line <= GetLastVisibleLine(); }
+        { return line >= GetVisibleBegin() && line < GetVisibleEnd(); }
+
+
+    // this is the same as GetVisibleBegin(), exists to match
+    // GetLastVisibleLine() and for backwards compatibility only
+    size_t GetFirstVisibleLine() const { return m_lineFirst; }
+
+    // get the last currently visible line
+    //
+    // this function is unsafe as it returns (size_t)-1 (i.e. a huge positive
+    // number) if the control is empty, use GetVisibleEnd() instead, this one
+    // is kept for backwards compatibility
+    size_t GetLastVisibleLine() const { return GetVisibleEnd() - 1; }
 
 
 protected:

src/generic/vscroll.cpp

@@ -220,7 +220,7 @@ void wxVScrolledWindow::RefreshLine(size_t line)
     wxRect rect;
     rect.width = GetClientSize().x;
     rect.height = OnGetLineHeight(line);
-    for ( size_t n = GetFirstVisibleLine(); n < line; n++ )
+    for ( size_t n = GetVisibleBegin(); n < line; n++ )
     {
         rect.y += OnGetLineHeight(n);
     }
@@ -235,21 +235,23 @@ void wxVScrolledWindow::RefreshLines(size_t from, size_t to)
 
     // clump the range to just the visible lines -- it is useless to refresh
     // the other ones
-    if ( from < GetFirstVisibleLine() )
-        from = GetFirstVisibleLine();
+    if ( from < GetVisibleBegin() )
+        from = GetVisibleBegin();
 
-    if ( to > GetLastVisibleLine() )
-        to = GetLastVisibleLine();
+    if ( to >= GetVisibleEnd() )
+        to = GetVisibleEnd();
+    else
+        to++;
 
     // calculate the rect occupied by these lines on screen
     wxRect rect;
     rect.width = GetClientSize().x;
-    for ( size_t nBefore = GetFirstVisibleLine(); nBefore < from; nBefore++ )
+    for ( size_t nBefore = GetVisibleBegin(); nBefore < from; nBefore++ )
     {
         rect.y += OnGetLineHeight(nBefore);
     }
 
-    for ( size_t nBetween = from; nBetween <= to; nBetween++ )
+    for ( size_t nBetween = from; nBetween < to; nBetween++ )
     {
         rect.height += OnGetLineHeight(nBetween);
     }
@@ -267,8 +269,8 @@ void wxVScrolledWindow::RefreshAll()
 
 int wxVScrolledWindow::HitTest(wxCoord WXUNUSED(x), wxCoord y) const
 {
-    const size_t lineMax = GetLastVisibleLine();
-    for ( size_t line = GetFirstVisibleLine(); line <= lineMax; line++ )
+    const size_t lineMax = GetVisibleEnd();
+    for ( size_t line = GetVisibleBegin(); line < lineMax; line++ )
     {
         y -= OnGetLineHeight(line);
         if ( y < 0 )
@@ -305,8 +307,8 @@ bool wxVScrolledWindow::ScrollToLine(size_t line)
 
 
     // remember the currently shown lines for the refresh code below
-    size_t lineFirstOld = GetFirstVisibleLine(),
-           lineLastOld = GetLastVisibleLine();
+    size_t lineFirstOld = GetVisibleBegin(),
+           lineLastOld = GetVisibleEnd();
 
     m_lineFirst = line;
 
@@ -317,8 +319,8 @@ bool wxVScrolledWindow::ScrollToLine(size_t line)
 
     // finally refresh the display -- but only redraw as few lines as possible
     // to avoid flicker
-    if ( GetFirstVisibleLine() > lineLastOld ||
-            GetLastVisibleLine() < lineFirstOld )
+    if ( GetVisibleBegin() >= lineLastOld ||
+            GetVisibleEnd() <= lineFirstOld )
     {
         // the simplest case: we don't have any old lines left, just redraw
         // everything
@@ -326,7 +328,7 @@ bool wxVScrolledWindow::ScrollToLine(size_t line)
     }
     else // overlap between the lines we showed before and should show now
     {
-        ScrollWindow(0, GetLinesHeight(GetFirstVisibleLine(), lineFirstOld));
+        ScrollWindow(0, GetLinesHeight(GetVisibleBegin(), lineFirstOld));
     }
 
     return true;
@@ -350,12 +352,14 @@ bool wxVScrolledWindow::ScrollPages(int pages)
         int line;
         if ( pages > 0 )
         {
-            line = GetLastVisibleLine();
+            line = GetVisibleEnd();
+            if ( line )
+                line--;
             pages--;
         }
         else // pages < 0
         {
-            line = FindFirstFromBottom(GetFirstVisibleLine());
+            line = FindFirstFromBottom(GetVisibleBegin());
             pages++;
         }
 
@@ -404,7 +408,9 @@ void wxVScrolledWindow::OnScroll(wxScrollWinEvent& event)
     }
     else if ( evtType == wxEVT_SCROLLWIN_PAGEDOWN )
     {
-        lineFirstNew = GetLastVisibleLine();
+        lineFirstNew = GetVisibleEnd();
+        if ( lineFirstNew )
+            lineFirstNew--;
     }
     else if ( evtType == wxEVT_SCROLLWIN_THUMBRELEASE )
     {