indicate current highlight mode in submenu

frontend/apps/reader/modules/readerhighlight.lua

@@ -71,9 +71,7 @@ end
 function ReaderHighlight:addToMainMenu(tab_item_table)
     -- insert table to main reader menu
     table.insert(tab_item_table.typeset, {
-        text_func = function()
+        text = _("Set highlight drawer "),
-            return _("Set highlight drawer ").."( "..self.view.highlight.saved_drawer.." )"
-        end,
         sub_item_table = self:genHighlightDrawerMenu(),
     })
 end
@@ -82,18 +80,27 @@ function ReaderHighlight:genHighlightDrawerMenu()
     return {
         {
             text = _("Lighten"),
+            enabled_func = function()
+                return self.view.highlight.saved_drawer ~= "lighten"
+            end,
             callback = function()
                 self.view.highlight.saved_drawer = "lighten"
             end
         },
         {
             text = _("Underscore"),
+            enabled_func = function()
+                return self.view.highlight.saved_drawer ~= "underscore"
+            end,
             callback = function()
                 self.view.highlight.saved_drawer = "underscore"
             end
         },
         {
             text = _("Invert"),
+            enabled_func = function()
+                return self.view.highlight.saved_drawer ~= "invert"
+            end,
             callback = function()
                 self.view.highlight.saved_drawer = "invert"
             end