Paging down in menu views does not operate correctly. This is particularly
noticeable using WQVGAlargeskin (Touch's large screen skin - a three line
display), where the action of paging down advances too far down the list,
causing some of the available menu items to be skipped from each successive
view. Refer 'Intended behaviour' for detail.

The appended patch implements the intended page down behaviour, and has been
tested on Squeezeplay 7.6.2 r9550 using each of the four skins. No change is
required to the existing page up code as this operates correctly.

Serendipitously, the present page down action does yield the intended
behaviour when using WQVGAsmallskin (a five line display). The existing code
fortuitously happens to do the right thing in this case.

If a skin implements a menu display with more than five lines, the action of
paging down will advance too slowly. This can be observed when using
QVGAportraitskin (six lines). A custom/future skin that implemented a larger
number of items in the menu view would also be impacted.


Intended behaviour
------------------

In a regular jive menu 'Page up' and 'Page down' actions are generated by:

  Touching (not sliding) the scroll bar, above or below the slider
  Mouse click - ditto
  Use of page up/page down keys

The action is intended to move forwards (page down) / backwards (page up)
through a list of menu items, page by page. As an aid to navigation, the
bottom/top item of the currently displayed view is shown as the top/bottom
item of the next displayed view.


Patch
-----

The patch appended below applies to jive/ui/Menu.lua, and implements the
intended 'Page down' behaviour. It has been tested on Squeezeplay 7.6.2 r9550
using all skins.
No change in behaviour will be observed when using WQVGAsmallskin, but
the behaviour will be as intended when using other skins.

[Diff file referenced to 7.6/trunk/squeezeplay]

Index: src/squeezeplay/share/jive/ui/Menu.lua
===================================================================
--- src/squeezeplay/share/jive/ui/Menu.lua	(revision 9550)
+++ src/squeezeplay/share/jive/ui/Menu.lua	(working copy)
@@ -507,10 +507,22 @@
 				return EVENT_CONSUME
 
 			elseif action == "page_down" then
-				--when paging down, bottom item becomes the bottom item
+				--when paging down, bottom item becomes the top item
 				if not self.selected or self.selected < self.listSize then
-					self:setSelectedIndex(self.topItem, true )
-					self:scrollBy(self.numWidgets + 2, true, false, false)
+
+					-- This is the inverse of the page_up action.
+					-- Sets current 'cursor' to the bottom item on the display
+					-- and then scrolls down by number of lines - 2.
+
+					-- Why '- 2' instead of the expected '- 1' ?
+					-- Answer: scrollBy will try to keep one item visible
+					-- below the new 'cursor' position. This has the effect of
+					-- scrolling by one more line than we intend.
+					
+					-- setSelectedIndex(i,true) keeps 'i' within bounds, no
+					-- check required on 'i' here.
+					self:setSelectedIndex(self.topItem + self.numWidgets - 1, true )
+					self:scrollBy(self.numWidgets - 2, true, false, false)
 				end
 				return EVENT_CONSUME