diff --git a/crereader.lua b/crereader.lua
index 880f99083..81e55dc73 100644
--- a/crereader.lua
+++ b/crereader.lua
@@ -25,7 +25,7 @@ function CREReader:open(filename)
 	end
 	local style_sheet = "./data/"..file_type..".css"
 	ok, self.doc = pcall(cre.openDocument, filename, style_sheet, 
-						width, height)
+						G_width, G_height)
 	if not ok then
 		return false, self.doc -- will contain error message
 	end
@@ -81,6 +81,8 @@ end
 ----------------------------------------------------
 function CREReader:goto(pos, pos_type)
 	local prev_xpointer = self.doc:getXPointer()
+	local width, height = G_width, G_height
+
 	if pos_type == "xpointer" then
 		self.doc:gotoXPointer(pos)
 		pos = self.doc:getCurrentPos()
@@ -125,11 +127,11 @@ function CREReader:gotoTocEntry(entry)
 end
 
 function CREReader:nextView()
-	return self.pos + height - self.pan_overlap_vertical
+	return self.pos + G_height - self.pan_overlap_vertical
 end
 
 function CREReader:prevView()
-	return self.pos - height + self.pan_overlap_vertical
+	return self.pos - G_height + self.pan_overlap_vertical
 end
 
 ----------------------------------------------------
@@ -174,10 +176,10 @@ end
 ----------------------------------------------------
 -- used in CREReader:showMenu()
 function CREReader:_drawReadingInfo()
-	local ypos = height - 50
+	local ypos = G_height - 50
 	local load_percent = self.percent/100
 
-	fb.bb:paintRect(0, ypos, width, 50, 0)
+	fb.bb:paintRect(0, ypos, G_width, 50, 0)
 
 	ypos = ypos + 15
 	local face, fhash = Font:getFaceAndHash(22)
@@ -189,7 +191,7 @@ function CREReader:_drawReadingInfo()
 		"Position: "..load_percent.."%".."    "..cur_section, true)
 
 	ypos = ypos + 15
-	blitbuffer.progressBar(fb.bb, 10, ypos, width-20, 15,
+	blitbuffer.progressBar(fb.bb, 10, ypos, G_width - 20, 15,
 							5, 4, load_percent/100, 8)
 end
 
@@ -254,7 +256,7 @@ function CREReader:adjustCreReaderCommands()
 				item_array = face_list,
 			}
 
-			local item_no = fonts_menu:choose(0, height)
+			local item_no = fonts_menu:choose(0, G_height)
 			print(face_list[item_no])
 			if item_no then
 				cr.doc:setFontFace(face_list[item_no])
diff --git a/djvureader.lua b/djvureader.lua
index c9ec0cdf4..460b2167d 100644
--- a/djvureader.lua
+++ b/djvureader.lua
@@ -66,13 +66,13 @@ function DJVUReader:_isEntireWordInScreenHeightRange(w)
 			(self.cur_full_height - (w.y1 * self.globalzoom) >=
 				-self.offset_y) and
 			(self.cur_full_height - (w.y0 * self.globalzoom) <= 
-				-self.offset_y + height)
+				-self.offset_y + G_height)
 end
 
 function DJVUReader:_isEntireWordInScreenWidthRange(w)
 	return	(w ~= nil) and
 			(w.x0 * self.globalzoom >= -self.offset_x) and
-			(w.x1 * self.globalzoom <= -self.offset_x + width)
+			(w.x1 * self.globalzoom <= -self.offset_x + G_width)
 end
 
 -- make sure at least part of the word can be seen in screen
@@ -81,9 +81,9 @@ function DJVUReader:_isWordInScreenRange(w)
 			(self.cur_full_height - (w.y0 * self.globalzoom) >=
 				-self.offset_y) and
 			(self.cur_full_height - (w.y1 * self.globalzoom) <= 
-				-self.offset_y + height) and
+				-self.offset_y + G_height) and
 			(w.x1 * self.globalzoom >= -self.offset_x) and
-			(w.x0 * self.globalzoom <= -self.offset_x + width)
+			(w.x0 * self.globalzoom <= -self.offset_x + G_width)
 end
 
 function DJVUReader:toggleTextHighLight(word_list)
diff --git a/filesearcher.lua b/filesearcher.lua
index da013f386..415dac45f 100644
--- a/filesearcher.lua
+++ b/filesearcher.lua
@@ -164,7 +164,7 @@ function FileSearcher:addAllCommands()
 		"invoke search inputbox",
 		function(self)
 			old_keywords = self.keywords
-			self.keywords = InputBox:input(height-100, 100,
+			self.keywords = InputBox:input(G_height - 100, 100,
 				"Search:", old_keywords)
 			if self.keywords then
 				self:setSearchResult(self.keywords)
@@ -181,7 +181,7 @@ function FileSearcher:addAllCommands()
 				menu_title = "Fonts Menu",
 				item_array = Font.fonts,
 			}
-			local re = fonts_menu:choose(0, height)
+			local re = fonts_menu:choose(0, G_height)
 			if re then
 				Font.cfont = Font.fonts[re]
 				Font:update()
@@ -195,14 +195,10 @@ function FileSearcher:addAllCommands()
 			file_entry = self.result[self.perpage*(self.page-1)+self.current]
 			file_full_path = file_entry.dir .. "/" .. file_entry.name
 
-			-- rotation mode might be changed while reading, so
-			-- record height_percent here
-			local height_percent = height/fb.bb:getHeight()
 			openFile(file_full_path)
-
 			--reset height and item index if screen has been rotated
 			local item_no = self.perpage * (self.page - 1) + self.current
-			self.perpage = math.floor(height / self.spacing) - 2
+			self.perpage = math.floor(G_height / self.spacing) - 2
 			self.current = item_no % self.perpage
 			self.page = math.floor(item_no / self.perpage) + 1
 
@@ -218,6 +214,7 @@ function FileSearcher:addAllCommands()
 end
 
 function FileSearcher:choose(keywords)
+	local width, height = G_width, G_height
 	self.perpage = math.floor(height / self.spacing) - 2
 	self.pagedirty = true
 	self.markerdirty = false
diff --git a/helppage.lua b/helppage.lua
index 33ba5e9a9..cedb17906 100644
--- a/helppage.lua
+++ b/helppage.lua
@@ -30,7 +30,7 @@ HelpPage.hface, HelpPage.hfhash = Font:getFaceAndHash(HelpPage.hfsize, "sans")
 HelpPage.ffsize = 15
 HelpPage.fface, HelpPage.ffhash = Font:getFaceAndHash(HelpPage.ffsize, "sans")
 
-function HelpPage:show(ypos, height,commands)
+function HelpPage:show(ypos, height, commands)
 	self.commands = {}
 	self.items = 0
 	local keys = {}
diff --git a/pdfreader.lua b/pdfreader.lua
index 9413e0127..334a69d85 100644
--- a/pdfreader.lua
+++ b/pdfreader.lua
@@ -13,7 +13,7 @@ function PDFReader:open(filename)
 		return false, self.doc -- will contain error message
 	end
 	if self.doc:needsPassword() then
-		local password = InputBox:input(height-100, 100, "Pass:")
+		local password = InputBox:input(G_height-100, 100, "Pass:")
 		if not password or not self.doc:authenticatePassword(password) then
 			self.doc:close()
 			self.doc = nil
diff --git a/reader.lua b/reader.lua
index 193eb768d..091f6f37b 100755
--- a/reader.lua
+++ b/reader.lua
@@ -121,7 +121,7 @@ if optarg["G"] ~= nil then
 end
 
 fb = einkfb.open("/dev/fb0")
-width, height = fb:getSize()
+G_width, G_height = fb:getSize()
 -- read current rotation mode
 Screen:updateRotationMode()
 Screen.native_rotation_mode = Screen.cur_rotation_mode
@@ -146,7 +146,7 @@ if ARGV[optind] and lfs.attributes(ARGV[optind], "mode") == "directory" then
 	local running = true
 	FileChooser:setPath(ARGV[optind])
 	while running do
-		local file, callback = FileChooser:choose(0,height)
+		local file, callback = FileChooser:choose(0, G_height)
 		if callback then
 			callback()
 		else
diff --git a/rendertext_example.lua b/rendertext_example.lua
index 12dbf524d..3c208b8f5 100755
--- a/rendertext_example.lua
+++ b/rendertext_example.lua
@@ -3,7 +3,7 @@ require "rendertext"
 require "graphics"
 
 fb = einkfb.open("/dev/fb0")
-width, height = fb:getSize()
+G_width, G_height = fb:getSize()
 
 print("open")
 
diff --git a/screen.lua b/screen.lua
index 0ac639044..25edb1096 100644
--- a/screen.lua
+++ b/screen.lua
@@ -77,6 +77,8 @@ function Screen:updateRotationMode()
 end
 
 function Screen:saveCurrentBB()
+	local width, height = G_width, G_height
+
 	if not self.saved_bb then
 		self.saved_bb = Blitbuffer.new(width, height)
 	end
@@ -92,7 +94,7 @@ function Screen:resotreFromSavedBB()
 end
 
 function Screen:getCurrentScreenBB()
-	local bb = Blitbuffer.new(width, height)
+	local bb = Blitbuffer.new(G_width, G_height)
 	bb:blitFullFrom(fb.bb)
 	return bb
 end
diff --git a/unireader.lua b/unireader.lua
index bc5294a8e..ad14cd5d2 100644
--- a/unireader.lua
+++ b/unireader.lua
@@ -250,6 +250,7 @@ function UniReader:drawOrCache(no, preCache)
 
 	-- ideally, this should be factored out and only be called when needed (TODO)
 	local ok, page = pcall(self.doc.openPage, self.doc, no)
+	local width, height = G_width, G_height
 	if not ok then
 		-- TODO: error handling
 		return nil
@@ -362,6 +363,7 @@ end
 function UniReader:setzoom(page, preCache)
 	local dc = DrawContext.new()
 	local pwidth, pheight = page:getSize(self.nulldc)
+	local width, height = G_width, G_height
 	print("# page::getSize "..pwidth.."*"..pheight);
 	local x0, y0, x1, y1 = page:getUsedBBox()
 	if x0 == 0.01 and y0 == 0.01 and x1 == -0.01 and y1 == -0.01 then
@@ -517,6 +519,8 @@ end
 -- render and blit a page
 function UniReader:show(no)
 	local pagehash, offset_x, offset_y = self:drawOrCache(no)
+	local width, height = G_width, G_height
+
 	if not pagehash then
 		return
 	end
@@ -662,7 +666,8 @@ function UniReader:nextView()
 			pageno = pageno + 1
 		else
 			-- goto next view of current page
-			self.offset_y = self.offset_y - height + self.pan_overlap_vertical
+			self.offset_y = self.offset_y - G_height
+							+ self.pan_overlap_vertical
 		end
 	else
 		-- not in fit to content width pan mode, just do a page turn
@@ -688,7 +693,8 @@ function UniReader:prevView()
 			pageno = pageno - 1
 		else
 			-- goto previous view of current page
-			self.offset_y = self.offset_y + height - self.pan_overlap_vertical
+			self.offset_y = self.offset_y + G_height
+							- self.pan_overlap_vertical
 		end
 	else
 		-- not in fit to content width pan mode, just do a page turn
@@ -735,7 +741,8 @@ end
 -- @ orien: 1 for clockwise rotate, -1 for anti-clockwise
 function UniReader:screenRotate(orien)
 	Screen:screenRotate(orien)
-	width, height = fb:getSize()
+	-- update global width and height variable
+	G_width, G_height = fb:getSize()
 	self:clearCache()
 	self:redrawCurrentPage()
 end
@@ -849,7 +856,7 @@ end
 
 -- used in UniReader:showMenu()
 function UniReader:_drawReadingInfo()
-	local ypos = height - 50
+	local width, height = G_width, G_height
 	local load_percent = (self.pageno / self.doc:getPages())
 	local face, fhash = Font:getFaceAndHash(22)
 
@@ -1060,7 +1067,7 @@ function UniReader:addAllCommands()
 	self.commands:add(KEY_G,nil,"G",
 		"goto page",
 		function(unireader)
-			local page = InputBox:input(height-100, 100, "Page:")
+			local page = InputBox:input(G_height-100, 100, "Page:")
 			-- convert string to number
 			if not pcall(function () page = page + 0 end) then
 				page = unireader.pageno
@@ -1074,7 +1081,7 @@ function UniReader:addAllCommands()
 	self.commands:add(KEY_H,nil,"H",
 		"show help page",
 		function(unireader)
-			HelpPage:show(0,height,unireader.commands)
+			HelpPage:show(0, G_height, unireader.commands)
 			unireader:redrawCurrentPage()
 		end)
 	self.commands:add(KEY_T,nil,"T",
@@ -1130,8 +1137,8 @@ function UniReader:addAllCommands()
 			local bbox = {}
 			bbox["x0"] = - unireader.offset_x / unireader.globalzoom
 			bbox["y0"] = - unireader.offset_y / unireader.globalzoom
-			bbox["x1"] = bbox["x0"] + width / unireader.globalzoom
-			bbox["y1"] = bbox["y0"] + height / unireader.globalzoom
+			bbox["x1"] = bbox["x0"] + G_width / unireader.globalzoom
+			bbox["y1"] = bbox["y0"] + G_height / unireader.globalzoom
 			bbox.pan_x = unireader.pan_x
 			bbox.pan_y = unireader.pan_y
 			unireader.bbox[unireader.pageno] = bbox
@@ -1176,8 +1183,8 @@ function UniReader:addAllCommands()
 					x = unireader.shift_x / 5
 					y = unireader.shift_y / 5
 				elseif unireader.pan_by_page then
-					x = width;
-					y = height - unireader.pan_overlap_vertical; -- overlap for lines which didn't fit
+					x = G_width;
+					y = G_height - unireader.pan_overlap_vertical; -- overlap for lines which didn't fit
 				else
 					x = unireader.shift_x
 					y = unireader.shift_y