add djvu render mode options in readermenu

frontend/apps/reader/modules/readermenu.lua

@@ -112,6 +112,9 @@ function ReaderMenu:setUpdateItemTable()
         end
     })
     table.insert(self.tab_item_table.setting, Language:getLangMenuTable())
+    if self.ui.document.is_djvu then
+        table.insert(self.tab_item_table.setting, self.view:getRenderModeMenuTable())
+    end
     table.insert(self.tab_item_table.setting, {
         text = _("Show advanced options"),
         checked_func = function() return G_reader_settings:readSetting("show_advanced") end,

frontend/apps/reader/modules/readerview.lua

@@ -1,12 +1,13 @@
+local ReaderFlipping = require("apps/reader/modules/readerflipping")
+local ReaderFooter = require("apps/reader/modules/readerfooter")
+local ReaderDogear = require("apps/reader/modules/readerdogear")
 local OverlapGroup = require("ui/widget/overlapgroup")
 local UIManager = require("ui/uimanager")
 local Screen = require("ui/screen")
 local Geom = require("ui/geometry")
 local Event = require("ui/event")
 local DEBUG = require("dbg")
-local ReaderFlipping = require("apps/reader/modules/readerflipping")
-local ReaderFooter = require("apps/reader/modules/readerfooter")
-local ReaderDogear = require("apps/reader/modules/readerdogear")
+local _ = require("gettext")
 
 local ReaderView = OverlapGroup:new{
     document = nil,
@@ -671,4 +672,26 @@ function ReaderView:autoSaveSettings()
     end
 end
 
+function ReaderView:getRenderModeMenuTable()
+    local view = self
+    local function make_mode(text, mode)
+        return {
+            text = text,
+            checked_func = function() return view.render_mode == mode end,
+            callback = function() view.render_mode = mode end,
+        }
+    end
+    return  {
+        text = _("DjVu render mode"),
+        sub_item_table = {
+            make_mode(_("COLOUR (works for both colour and b&w pages)"), 0),
+            make_mode(_("BLACK & WHITE (for b&w pages only, much faster)"), 1),
+            make_mode(_("COLOUR ONLY (slightly faster than COLOUR)"), 2),
+            make_mode(_("MASK ONLY (for b&w pages only)"), 3),
+            make_mode(_("COLOUR BACKGROUND (show only background)"), 4),
+            make_mode(_("COLOUR FOREGROUND (show only foreground)"), 5),
+        }
+    }
+end
+
 return ReaderView

frontend/document/djvudocument.lua

@@ -9,6 +9,7 @@ local Configurable = require("configurable")
 local DjvuDocument = Document:new{
     _document = false,
     -- libdjvulibre manages its own additional cache, default value is hard written in c module.
+    is_djvu = true,
     djvulibre_cache_size = nil,
     dc_null = DrawContext.new(),
     options = KoptOptions,