helpers: import scroll from Remy Clouard

First scroll helper, that provides an alternative to truncate. Text
shifts every time the widget is updated, there is no internal timer.

helpers.lua

@@ -1,6 +1,7 @@
 ---------------------------------------------------
 -- Licensed under the GNU General Public License v2
---  * (c) 2009, Adrian C. <anrxc.sysphere.org>
+--  * (c) 2009, Adrian C. <anrxc@sysphere.org>
+--  * (c) 2009, Rémy C. <shikamaru@mandriva.org>
 --  * (c) Wicked, Lucas de Vries
 ---------------------------------------------------
 
@@ -17,6 +18,11 @@ local string = {
 module("vicious.helpers")
 
 
+-- {{{ Variable definitions
+local scroller = {}
+-- }}}
+
+-- {{{ Helper functions
 -- {{{ Format a string with args
 function format(format, args)
     for var, val in pairs(args) do
@@ -27,7 +33,7 @@ function format(format, args)
 end
 -- }}}
 
---{{{ Escape a string
+-- {{{ Escape a string
 function escape(text)
     local xml_entities = {
         ["\""] = "&quot;",
@@ -41,14 +47,46 @@ function escape(text)
 end
 -- }}}
 
---{{{ Truncate a string
+-- {{{ Truncate a string
 function truncate(text, maxlen)
     local txtlen = text:len()
 
     if txtlen > maxlen then
-        text = text:sub(1, maxlen - 3) .. "..."
+        text = string.sub(text, 1, maxlen - 3) .. "..."
     end
 
     return text
 end
 -- }}}
+
+-- {{{ Scroll through a string
+function scroll(text, maxlen, widget)
+    if not scroller[widget] then
+        scroller[widget] = { i = 1, d = true }
+    end
+
+    local txtlen = text:len()
+    local state  = scroller[widget]
+
+    if txtlen > maxlen then
+        if state.d then
+            text = string.sub(text, state.i, state.i + maxlen) .. "..."
+            state.i = state.i + 3
+
+            if maxlen + state.i >= txtlen then
+                state.d = false
+            end
+        else
+            text = "..." .. string.sub(text, state.i, state.i + maxlen)
+            state.i = state.i - 3
+
+            if state.i <= 1 then
+                state.d = true
+            end
+        end
+    end
+
+    return text
+end
+-- }}}
+-- }}}