documented Left[Is]Down behaviour and changed the obsolete test in the sample

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_2_BRANCH@7609 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/mouseevt.tex

@@ -9,6 +9,20 @@ drawbacks: the LEAVE\_WINDOW event might be received some time after the mouse
 left the window and the state variables for it may have changed during this
 time.
 
+{\bf NB: } Note the difference between methods like 
+\helpref{LeftDown}{wxmouseeventleftdown} and 
+\helpref{LeftIsDown}{wxmouseeventleftisdown}: the formet returns {\tt TRUE}
+when the event corresponds to the left mouse button click while the latter
+returns {\tt TRUE} if the left mouse button is currently being pressed. For
+example, when the user is dragging the mouse you can use 
+\helpref{LeftIsDown}{wxmouseeventleftisdown} to test
+whether the left mouse button is (still) depressed. Also, by convention, if
+\helpref{LeftDown}{wxmouseeventleftdown} returns {\tt TRUE}, 
+\helpref{LeftIsDown}{wxmouseeventleftisdown} will also return {\tt TRUE} in
+wxWindows whatever the underlying GUI behaviour is (which is
+platform-dependent). The same applies, of course, to other mouse buttons as
+well.
+
 \wxheading{Derived from}
 
 \helpref{wxEvent}{wxevent}

samples/scroll/scroll.cpp

@@ -188,12 +188,9 @@ void MyCanvas::OnMouseDown( wxMouseEvent &event )
         int x,y;
         CalcUnscrolledPosition( pt.x, pt.y, &x, &y );
         wxLogMessage( "Mouse down event at: %d %d, scrolled: %d %d", pt.x, pt.y, x, y );
-    }
 
-    if (event.LeftIsDown() &&
-        event.LeftDown())
-    {
-        wxLogMessage( "Error: both LeftDown() and LeftIsDown() are TRUE!" );
+        if ( !event.LeftIsDown() )
+            wxLogMessage( "Error: LeftIsDown() should be TRUE if for LeftDown()" );
     }
 }