Move render_mode support out of unireader.lua into djvureader.lua as it is djvu-specific.

Also added support for all other rendering modes handled by djvulibre.
Also made the message print a human-readable description of the mode rather than just the number.

djvu.c

@@ -401,15 +401,9 @@ static int drawPage(lua_State *L) {
 	DrawContext *dc = (DrawContext*) luaL_checkudata(L, 2, "drawcontext");
 	BlitBuffer *bb = (BlitBuffer*) luaL_checkudata(L, 3, "blitbuffer");
 	int render_mode = (int) luaL_checkint(L, 6);
-	ddjvu_render_mode_t djvu_render_mode;
+	ddjvu_render_mode_t djvu_render_mode = render_mode;
 	unsigned char adjusted_low[16], adjusted_high[16];
 	int i, adjust_pixels = 0;
-
-	if (render_mode)
-		djvu_render_mode = DDJVU_RENDER_BLACK;
-	else
-		djvu_render_mode = DDJVU_RENDER_COLOR;
-
 	ddjvu_format_t *pixelformat;
 	ddjvu_rect_t pagerect, renderrect;
 	uint8_t *imagebuffer = NULL;

djvureader.lua

@@ -21,8 +21,48 @@ end
 function DJVUReader:adjustDjvuReaderCommand()
 	self.commands:del(KEY_J, MOD_SHIFT, "J")
 	self.commands:del(KEY_K, MOD_SHIFT, "K")
+	self.commands:add(KEY_R, nil, "R",
+		"colour/b&w/colouronly/maskonly/backg/foreg",
+		function(self)
+			self:cycle_render_mode()
+	end) 
 end
 
+-- cycle through all rendering modes supported by djvulibre:
+--  0	(color page or stencil)
+--  1	(stencil or color page)
+--  2	(color page or fail)
+--  3	(stencil or fail)
+--  4	(color background layer)
+--  5	(color foreground layer)
+--  Note that if the values in the definition of ddjvu_render_mode_t in djvulibre/libdjvu/ddjvuapi.h change,
+--  then we should update our values here also. This is a bit risky, but these values never change, so it should be ok :)
+function DJVUReader:cycle_render_mode()
+	self.render_mode = (self.render_mode + 1)%6
+	Debug("cycle_render_mode, render_mode=", self.render_mode)
+	self:clearCache()
+	self.doc:cleanCache()
+	local render_mode_name
+	if self.render_mode == 0 then
+		render_mode_name = "COLOUR"
+	elseif self.render_mode == 1 then
+		render_mode_name = "BLACK & WHITE"
+	elseif self.render_mode == 2 then
+		render_mode_name = "COLOUR ONLY"
+	elseif self.render_mode == 3 then
+		render_mode_name = "MASK ONLY"
+	elseif self.render_mode == 4 then
+		render_mode_name = "COLOUR BACKGROUND"
+	elseif self.render_mode == 5 then
+		render_mode_name = "COLOUR FOREGROUND"
+	else
+		render_mode_name = "UNKNOWN"
+	end
+	showInfoMsgWithDelay("("..self.render_mode..") "..render_mode_name, 1000, 1)
+	self:redrawCurrentPage()
+end
+
+
 
 ----------------------------------------------------
 -- highlight support 

unireader.lua

@@ -34,9 +34,9 @@ UniReader = {
 	-- gamma setting:
 	globalgamma = 1.0,   -- GAMMA_NO_GAMMA
 
-	-- rendering mode toggle (used in djvu.c:drawPage())
-	-- if set to 1 render in BLACK & WHITE, otherwise COLOR
-	render_mode = 1,
+	-- DjVu page rendering mode (used in djvu.c:drawPage())
+	-- See comments in djvureader.lua:DJVUReader:cycle_render_mode()
+	render_mode = 0, -- COLOUR
 
 	-- cached tile size
 	fullwidth = 0,
@@ -1576,16 +1576,6 @@ function UniReader:modifyGamma(factor)
 	self:redrawCurrentPage()
 end
 
--- toggle rendering mode between colour (0) and b&w (1)
-function UniReader:toggle_render_mode()
-	Debug("toggle_render_mode, render_mode=", self.render_mode)
-	self.render_mode = 1 - self.render_mode
-	self:clearCache()
-	self.doc:cleanCache()
-	showInfoMsgWithDelay("New render_mode = "..self.render_mode, 1000, 1)
-	self:redrawCurrentPage()
-end
-
 -- adjust zoom state and trigger re-rendering
 function UniReader:setglobalzoom_mode(newzoommode)
 	if self.globalzoom_mode ~= newzoommode then
@@ -2217,11 +2207,6 @@ function UniReader:addAllCommands()
 				self:redrawCurrentPage()
 			end
 		end)
-	self.commands:add(KEY_R, nil, "R",
-		"toggle rendering mode: b&w/colour",
-		function(unireader)
-			unireader:toggle_render_mode()
-		end)
 	self.commands:add(KEY_R, MOD_SHIFT, "R",
 		"manual full screen refresh",
 		function(unireader)