koreader/frontend/ui/reader/readerpaging.lua

local InputContainer = require("ui/widget/container/inputcontainer")
local Screen = require("ui/screen")
local Geom = require("ui/geometry")
local Input = require("ui/input")
local GestureRange = require("ui/gesturerange")
local Device = require("ui/device")
local Event = require("ui/event")
local UIManager = require("ui/uimanager")
local Math = require("optmath")
local DEBUG = require("dbg")
local _ = require("gettext")

local ReaderPaging = InputContainer:new{
	current_page = 0,
	number_of_pages = 0,
	last_pan_relative_y = 0,
	visible_area = nil,
	page_area = nil,
	show_overlap_enable = nil,
	overlap = Screen:scaleByDPI(DOVERLAPPIXELS),
	
	page_flipping_mode = false,
	bookmark_flipping_mode = false,
	flip_steps = {0,1,2,5,10,20,50,100}
}

function ReaderPaging:init()
	if Device:hasKeyboard() then
		self.key_events = {
			GotoNextPage = {
				{Input.group.PgFwd}, doc = "go to next page",
				event = "GotoPageRel", args = 1 },
			GotoPrevPage = {
				{Input.group.PgBack}, doc = "go to previous page",
				event = "GotoPageRel", args = -1 },

			GotoFirst = {
				{"1"}, doc = "go to start", event = "GotoPercent", args = 0},
			Goto11 = {
				{"2"}, doc = "go to 11%", event = "GotoPercent", args = 11},
			Goto22 = {
				{"3"}, doc = "go to 22%", event = "GotoPercent", args = 22},
			Goto33 = {
				{"4"}, doc = "go to 33%", event = "GotoPercent", args = 33},
			Goto44 = {
				{"5"}, doc = "go to 44%", event = "GotoPercent", args = 44},
			Goto55 = {
				{"6"}, doc = "go to 55%", event = "GotoPercent", args = 55},
			Goto66 = {
				{"7"}, doc = "go to 66%", event = "GotoPercent", args = 66},
			Goto77 = {
				{"8"}, doc = "go to 77%", event = "GotoPercent", args = 77},
			Goto88 = {
				{"9"}, doc = "go to 88%", event = "GotoPercent", args = 88},
			GotoLast = {
				{"0"}, doc = "go to end", event = "GotoPercent", args = 100},
		}
	end
	self.number_of_pages = self.ui.document.info.number_of_pages
	self.ui.menu:registerToMainMenu(self)
end

-- This method will  be called in onSetDimensions handler
function ReaderPaging:initGesListener()
	self.ges_events = {
		TapForward = {
			GestureRange:new{
				ges = "tap",
				range = Geom:new{
					x = Screen:getWidth()*DTAP_ZONE_FORWARD.x,
					y = Screen:getHeight()*DTAP_ZONE_FORWARD.y,
					w = Screen:getWidth()*DTAP_ZONE_FORWARD.w,
					h = Screen:getHeight()*DTAP_ZONE_FORWARD.h,
				}
			}
		},
		TapBackward = {
			GestureRange:new{
				ges = "tap",
				range = Geom:new{
					x = Screen:getWidth()*DTAP_ZONE_BACKWARD.x,
					y = Screen:getHeight()*DTAP_ZONE_BACKWARD.y,
					w = Screen:getWidth()*DTAP_ZONE_BACKWARD.w,
					h = Screen:getHeight()*DTAP_ZONE_BACKWARD.h,
				}
			}
		},
		Swipe = {
			GestureRange:new{
				ges = "swipe",
				range = Geom:new{
					x = 0, y = 0,
					w = Screen:getWidth(),
					h = Screen:getHeight(),
				}
			}
		},
		Pan = {
			GestureRange:new{
				ges = "pan",
				range = Geom:new{
					x = 0, y = 0,
					w = Screen:getWidth(),
					h = Screen:getHeight(),
				},
				rate = 4.0,
			}
		},
		PanRelease = {
			GestureRange:new{
				ges = "pan_release",
				range = Geom:new{
					x = 0, y = 0,
					w = Screen:getWidth(),
					h = Screen:getHeight(),
				},
			}
		},
	}
end

function ReaderPaging:onReadSettings(config)
	self.page_positions = config:readSetting("page_positions") or {}
	self:gotoPage(config:readSetting("last_page") or 1)
	self.show_overlap_enable = config:readSetting("show_overlap_enable")
	if self.show_overlap_enable == nil then
		self.show_overlap_enable = DSHOWOVERLAP
	end
end

function ReaderPaging:onSaveSettings()
	self.ui.doc_settings:saveSetting("page_positions", self.page_positions)
	self.ui.doc_settings:saveSetting("last_page", self:getTopPage())
	self.ui.doc_settings:saveSetting("percent_finished", self.current_page/self.number_of_pages)
	self.ui.doc_settings:saveSetting("show_overlap_enable", self.show_overlap_enable)
end

function ReaderPaging:addToMainMenu(tab_item_table)
	if self.ui.document.info.has_pages then
		table.insert(tab_item_table.typeset, {
			text_func = function() 
				return self.show_overlap_enable and 
				_("Turn off page overlap") or 
				_("Turn on page overlap")
			end,
			callback = function()
				self.show_overlap_enable = not self.show_overlap_enable
			end
		})
	end
end

--[[
Set reading position on certain page
Page position is a fractional number ranging from 0 to 1, indicating the read percentage on
certain page. With the position information on each page whenever users change font size, 
page margin or line spacing or close and reopen the book, the page view will be roughly the same.
--]]
function ReaderPaging:setPagePosition(page, pos)
	DEBUG("set page position", pos)
	self.page_positions[page] = pos
end

--[[
Get reading position on certain page
--]]
function ReaderPaging:getPagePosition(page)
	-- Page number ought to be integer, somehow I notice that with 
	-- fractional page number the reader runs silently well, but the 
	-- number won't fit to retrieve page position. 
	page = math.floor(page)
	DEBUG("get page position", self.page_positions[page])
	return self.page_positions[page] or 0
end

function ReaderPaging:onTapForward()
	self:onPagingRel(1)
	return true
end

function ReaderPaging:onTapBackward()
	self:onPagingRel(-1)
	return true
end

function ReaderPaging:onTogglePageFlipping()
	self.view.flipping_visible = not self.view.flipping_visible
	self.page_flipping_mode = self.view.flipping_visible
	self.flipping_page = self.current_page
	
	if self.page_flipping_mode then
		self:updateOriginalPage(self.current_page)
		self:enterFlippingMode()
	else
		self:updateOriginalPage(nil)
		self:exitFlippingMode()
	end
	self.view:resetLayout()
	self.ui:handleEvent(Event:new("SetHinting", not self.page_flipping_mode))
	self.ui:handleEvent(Event:new("ReZoom"))
	UIManager:setDirty(self.view.dialog, "partial")
end

function ReaderPaging:onToggleBookmarkFlipping()
	 self.bookmark_flipping_mode = not self.bookmark_flipping_mode
	
	if self.bookmark_flipping_mode then
		self.orig_flipping_mode = self.view.flipping_visible
		self.orig_dogear_mode = self.view.dogear_visible
		
		self.view.flipping_visible = true
		self.view.dogear_visible = true
		self.bm_flipping_orig_page = self.current_page
		self:enterFlippingMode()
	else
		self.view.flipping_visible = self.orig_flipping_mode
		self.view.dogear_visible = self.orig_dogear_mode
		self:exitFlippingMode()
		self:gotoPage(self.bm_flipping_orig_page)
	end
	self.view:resetLayout()
	self.ui:handleEvent(Event:new("SetHinting", not self.bookmark_flipping_mode))
	self.ui:handleEvent(Event:new("ReZoom"))
	UIManager:setDirty(self.view.dialog, "partial")
end

function ReaderPaging:enterFlippingMode()
	self.orig_reflow_mode = self.view.document.configurable.text_wrap
	self.orig_footer_mode = self.view.footer_visible
	self.orig_scroll_mode = self.view.page_scroll
	self.orig_zoom_mode = self.view.zoom_mode
	DEBUG("store zoom mode", self.orig_zoom_mode)
	self.DGESDETECT_DISABLE_DOUBLE_TAP = DGESDETECT_DISABLE_DOUBLE_TAP
	
	self.view.document.configurable.text_wrap = 0
	self.view.page_scroll = false
	self.view.footer_visible = true
	Input.disable_double_tap = false
	DGESDETECT_DISABLE_DOUBLE_TAP = false
	self.ui:handleEvent(Event:new("SetZoomMode", "page"))
end

function ReaderPaging:exitFlippingMode()
	self.view.document.configurable.text_wrap = self.orig_reflow_mode
	self.view.page_scroll = self.orig_scroll_mode
	self.view.footer_visible = self.orig_footer_mode
	DGESDETECT_DISABLE_DOUBLE_TAP = self.DGESDETECT_DISABLE_DOUBLE_TAP
	Input.disable_double_tap = DGESDETECT_DISABLE_DOUBLE_TAP
	DEBUG("restore zoom mode", self.orig_zoom_mode)
	self.ui:handleEvent(Event:new("SetZoomMode", self.orig_zoom_mode))
end

function ReaderPaging:updateOriginalPage(page)
	self.original_page = page
end

function ReaderPaging:updateFlippingPage(page)
	self.flipping_page = page
end

function ReaderPaging:pageFlipping(flipping_page, flipping_ges)
	local whole = self.number_of_pages
	local steps = #self.flip_steps
	local stp_proportion = flipping_ges.distance / Screen:getWidth()
	local abs_proportion = flipping_ges.distance / Screen:getHeight()
	if flipping_ges.direction == "east" then
		self:gotoPage(flipping_page - self.flip_steps[math.ceil(steps*stp_proportion)])
	elseif flipping_ges.direction == "west" then
		self:gotoPage(flipping_page + self.flip_steps[math.ceil(steps*stp_proportion)])
	elseif flipping_ges.direction == "south" then
		self:gotoPage(flipping_page - math.floor(whole*abs_proportion))
	elseif flipping_ges.direction == "north" then
		self:gotoPage(flipping_page + math.floor(whole*abs_proportion))
	end
	UIManager:setDirty(self.view.dialog, "partial")
end

function ReaderPaging:bookmarkFlipping(flipping_page, flipping_ges)
	if flipping_ges.direction == "east" then
		self.ui:handleEvent(Event:new("GotoPreviousBookmark", flipping_page))
	elseif flipping_ges.direction == "west" then
		self.ui:handleEvent(Event:new("GotoNextBookmark", flipping_page))
	end
	UIManager:setDirty(self.view.dialog, "partial")
end

function ReaderPaging:onSwipe(arg, ges)
	if self.bookmark_flipping_mode then
		self:bookmarkFlipping(self.current_page, ges)
	elseif self.page_flipping_mode and self.original_page then
		self:gotoPage(self.original_page)
	elseif ges.direction == "west" then
		self:onPagingRel(1)
	elseif ges.direction == "east" then
		self:onPagingRel(-1)
	else
		UIManager.full_refresh = true
	end
	return true
end

function ReaderPaging:onPan(arg, ges)
	if self.bookmark_flipping_mode then
		return true
	elseif self.page_flipping_mode then
		if self.view.zoom_mode == "page" then
			self:pageFlipping(self.flipping_page, ges)
		else
			self.view:PanningStart(-ges.relative.x, -ges.relative.y)
		end
	elseif ges.direction == "north" or ges.direction == "south" then
		self:onPanningRel(self.last_pan_relative_y - ges.relative.y)
		self.last_pan_relative_y = ges.relative.y
	end
	return true
end

function ReaderPaging:onPanRelease(arg, ges)
	if self.page_flipping_mode then
		if self.view.zoom_mode == "page" then
			self:updateFlippingPage(self.current_page)
		else
			self.view:PanningStop()
		end
	else
		self.last_pan_relative_y = 0
		UIManager.full_refresh = true
	end
end

function ReaderPaging:onZoomModeUpdate(new_mode)
	-- we need to remember zoom mode to handle page turn event
	self.zoom_mode = new_mode
end

function ReaderPaging:onPageUpdate(new_page_no, orig)
	self.current_page = new_page_no
	if orig ~= "scrolling" then
		self.ui:handleEvent(Event:new("InitScrollPageStates", orig))
	end
end

function ReaderPaging:onViewRecalculate(visible_area, page_area)
	-- we need to remember areas to handle page turn event
	self.visible_area = visible_area:copy()
	self.page_area = page_area
end

function ReaderPaging:onGotoPercent(percent)
	DEBUG("goto document offset in percent:", percent)
	local dest = math.floor(self.number_of_pages * percent / 100)
	if dest < 1 then dest = 1 end
	if dest > self.number_of_pages then
		dest = self.number_of_pages
	end
	self:gotoPage(dest)
	return true
end

function ReaderPaging:onPagingRel(diff)
	if self.view.page_scroll then
		self:onScrollPageRel(diff)
	else
		self:onGotoPageRel(diff)
	end
	self:setPagePosition(self:getTopPage(), self:getTopPosition())
	return true
end

function ReaderPaging:onPanningRel(diff)
	if self.view.page_scroll then
		self:onScrollPanRel(diff)
	end
	self:setPagePosition(self:getTopPage(), self:getTopPosition())
	return true
end

--[[
Get read percentage on current page.
--]]
function ReaderPaging:getTopPosition()
	if self.view.page_scroll then
		local state = self.view.page_states[1]
		return (state.visible_area.y - state.page_area.y)/state.page_area.h
	else
		return 0
	end
end

--[[
Get page number of the page drawn at the very top part of the screen.
--]]
function ReaderPaging:getTopPage()
	if self.view.page_scroll then
		local state = self.view.page_states[1]
		return state and state.page or self.current_page
	else
		return self.current_page
	end
end

function ReaderPaging:onInitScrollPageStates(orig)
	--DEBUG.traceback()
	DEBUG("init scroll page states", orig)
	if self.view.page_scroll and self.view.state.page then
		self.orig_page = self.current_page
		self.view.page_states = {}
		local blank_area = Geom:new{}
		blank_area:setSizeTo(self.view.dimen)
		while blank_area.h > 0 do
			local offset = Geom:new{}
			-- caculate position in current page
			if self.current_page == self.orig_page then
				local page_area = self.view:getPageArea(
					self.view.state.page,
					self.view.state.zoom,
					self.view.state.rotation)
				offset.y = page_area.h * self:getPagePosition(self.current_page)
			end
			local state = self:getNextPageState(blank_area, offset)
			--DEBUG("init new state", state)
			table.insert(self.view.page_states, state)
			if blank_area.h > 0 then
				blank_area.h = blank_area.h - self.view.page_gap.height
			end
			if blank_area.h > 0 then
				self:gotoPage(self.current_page + 1, "scrolling")
			end
		end
		self:gotoPage(self.orig_page, "scrolling")
	end
	return true
end

function ReaderPaging:onUpdateScrollPageRotation(rotation)
	for _, state in ipairs(self.view.page_states) do
		state.rotation = rotation
	end
	return true
end

function ReaderPaging:onUpdateScrollPageGamma(gamma)
	for _, state in ipairs(self.view.page_states) do
		state.gamma = gamma
	end
	return true
end

function ReaderPaging:getNextPageState(blank_area, offset)
	local page_area = self.view:getPageArea(
		self.view.state.page,
		self.view.state.zoom,
		self.view.state.rotation)
	local visible_area = Geom:new{x = 0, y = 0}
	visible_area.w, visible_area.h = blank_area.w, blank_area.h
	visible_area.x, visible_area.y = page_area.x, page_area.y
	visible_area = visible_area:shrinkInside(page_area, offset.x, offset.y)
	-- shrink blank area by the height of visible area
	blank_area.h = blank_area.h - visible_area.h
	return {
		page = self.view.state.page,
		zoom = self.view.state.zoom,
		rotation = self.view.state.rotation,
		gamma = self.view.state.gamma,
		offset = Geom:new{ x = self.view.state.offset.x, y = 0},
		visible_area = visible_area,
		page_area = page_area,
	}
end

function ReaderPaging:getPrevPageState(blank_area, offset)
	local page_area = self.view:getPageArea(
		self.view.state.page,
		self.view.state.zoom,
		self.view.state.rotation)
	local visible_area = Geom:new{x = 0, y = 0}
	visible_area.w, visible_area.h = blank_area.w, blank_area.h
	visible_area.x = page_area.x
	visible_area.y = page_area.y + page_area.h - visible_area.h
	visible_area = visible_area:shrinkInside(page_area, offset.x, offset.y)
	-- shrink blank area by the height of visible area
	blank_area.h = blank_area.h - visible_area.h
	return {
		page = self.view.state.page,
		zoom = self.view.state.zoom,
		rotation = self.view.state.rotation,
		gamma = self.view.state.gamma,
		offset = Geom:new{ x = self.view.state.offset.x, y = 0},
		visible_area = visible_area,
		page_area = page_area,
	}
end

function ReaderPaging:updateTopPageState(state, blank_area, offset)
	local visible_area = Geom:new{x = 0, y = 0}
	visible_area.w, visible_area.h = blank_area.w, blank_area.h
	visible_area.x, visible_area.y = state.visible_area.x, state.visible_area.y
	if state.page == self.number_of_pages then
		visible_area:offsetWithin(state.page_area, offset.x, offset.y)
	else
		visible_area = visible_area:shrinkInside(state.page_area, offset.x, offset.y)
	end
	-- shrink blank area by the height of visible area
	blank_area.h = blank_area.h - visible_area.h
	state.visible_area = visible_area
	return state
end

function ReaderPaging:updateBottomPageState(state, blank_area, offset)
	local visible_area = Geom:new{x = 0, y = 0}
	visible_area.w, visible_area.h = blank_area.w, blank_area.h
	visible_area.x = state.page_area.x
	visible_area.y = state.visible_area.y + state.visible_area.h - visible_area.h
	if state.page == 1 then
		visible_area:offsetWithin(state.page_area, offset.x, offset.y)
	else
		visible_area = visible_area:shrinkInside(state.page_area, offset.x, offset.y)
	end
	-- shrink blank area by the height of visible area
	blank_area.h = blank_area.h - visible_area.h
	state.visible_area = visible_area
	return state
end

function ReaderPaging:genPageStatesFromTop(top_page_state, blank_area, offset)
	-- Offset should always be greater than 0
	-- otherwise if offset is less than 0 the height of blank area will be
	-- larger than 0 even if page area is much larger than visible area,
	-- which will trigger the drawing of next page leaving part of current
	-- page undrawn. This should also be true for generating from bottom.
	if offset.y < 0 then offset.y = 0 end
	local state = self:updateTopPageState(top_page_state, blank_area, offset)
	--DEBUG("updated state", state)
	local page_states = {}
	if state.visible_area.h > 0 then
		table.insert(page_states, state)
	end
	--DEBUG("blank area", blank_area)
	local current_page = state.page
	while blank_area.h > 0 do
		blank_area.h = blank_area.h - self.view.page_gap.height
		if blank_area.h > 0 then
			if self.current_page == self.number_of_pages then break end
			self:gotoPage(current_page + 1, "scrolling")
			current_page = current_page + 1
			local state = self:getNextPageState(blank_area, Geom:new{})
			--DEBUG("new state", state)
			table.insert(page_states, state)
		end
	end
	return page_states
end

function ReaderPaging:genPageStatesFromBottom(bottom_page_state, blank_area, offset)
	-- scroll up offset should always be less than 0
	if offset.y > 0 then offset.y = 0 end
	local state = self:updateBottomPageState(bottom_page_state, blank_area, offset)
	--DEBUG("updated state", state)
	local page_states = {}
	if state.visible_area.h > 0 then
		table.insert(page_states, state)
	end
	--DEBUG("blank area", blank_area)
	local current_page = state.page
	while blank_area.h > 0 do
		blank_area.h = blank_area.h - self.view.page_gap.height
		if blank_area.h > 0 then
			if self.current_page == 1 then break end
			self:gotoPage(current_page - 1, "scrolling")
			current_page = current_page - 1
			local state = self:getPrevPageState(blank_area, Geom:new{})
			--DEBUG("new state", state)
			table.insert(page_states, 1, state)
		end
	end
	return page_states
end

function ReaderPaging:onScrollPanRel(diff)
	DEBUG("pan relative height:", diff)
	local blank_area = Geom:new{}
	blank_area:setSizeTo(self.view.dimen)
	if diff > 0 then
		local first_page_state = table.remove(self.view.page_states, 1)
		local offset = Geom:new{
			x = 0,
			y = diff,
		}
		self.view.page_states = self:genPageStatesFromTop(first_page_state, blank_area, offset)
	end
	if diff < 0 then
		local last_page_state = table.remove(self.view.page_states)
		local offset = Geom:new{
			x = 0,
			y = diff
		}
		self.view.page_states = self:genPageStatesFromBottom(last_page_state, blank_area, offset)
	end
	-- update current pageno to the very last part in current view
	self:gotoPage(self.view.page_states[#self.view.page_states].page, "scrolling")
	
	UIManager:setDirty(self.view.dialog, "fast")
end

function ReaderPaging:onScrollPageRel(diff)
	DEBUG("scroll relative page:", diff)
	local blank_area = Geom:new{}
	blank_area:setSizeTo(self.view.dimen)
	if diff > 0 then
		local last_page_state = table.remove(self.view.page_states)
		local offset = Geom:new{
			x = 0,
			y = last_page_state.visible_area.h - self.overlap
		}
		self.view.page_states = self:genPageStatesFromTop(last_page_state, blank_area, offset)
	end
	if diff < 0 then
		local first_page_state = table.remove(self.view.page_states, 1)
		local offset = Geom:new{
			x = 0,
			y = -first_page_state.visible_area.h + self.overlap
		}
		self.view.page_states = self:genPageStatesFromBottom(first_page_state, blank_area, offset)
	end
	-- update current pageno to the very last part in current view
	self:gotoPage(self.view.page_states[#self.view.page_states].page, "scrolling")
	UIManager:setDirty(self.view.dialog)
end

function ReaderPaging:onGotoPageRel(diff)
	DEBUG("goto relative page:", diff)
	local new_va = self.visible_area:copy()
	local x_pan_off, y_pan_off = 0, 0

	if self.zoom_mode == "free" then
		-- do nothing in free zoom mode
	elseif self.zoom_mode:find("width") then
		y_pan_off = self.visible_area.h * diff
	elseif self.zoom_mode:find("height") then
		x_pan_off = self.visible_area.w * diff
	else
		-- must be fit content or page zoom mode
		if self.visible_area.w == self.page_area.w then
			y_pan_off = self.visible_area.h * diff
		else
			x_pan_off = self.visible_area.w * diff
		end
	end
	-- adjust offset to help with page turn decision
	-- we dont take overlap into account here yet, otherwise new_va will
	-- always intersect with page_area
	x_pan_off = Math.roundAwayFromZero(x_pan_off)
	y_pan_off = Math.roundAwayFromZero(y_pan_off)
	new_va.x = Math.roundAwayFromZero(self.visible_area.x+x_pan_off)
	new_va.y = Math.roundAwayFromZero(self.visible_area.y+y_pan_off)

	if new_va:notIntersectWith(self.page_area) then
		-- view area out of page area, do a page turn
		self:gotoPage(self.current_page + diff)
		-- if we are going back to previous page, reset
		-- view area to bottom of previous page
		if x_pan_off < 0 then
			self.view:PanningUpdate(self.page_area.w, 0)
		elseif y_pan_off < 0 then
			self.view:PanningUpdate(0, self.page_area.h)
		end
		-- reset dim_area
		--self.view.dim_area.h = 0
		--self.view.dim_area.w = 0
		--
	else
		-- not end of page yet, goto next view
		-- adjust panning step according to overlap
		if x_pan_off > self.overlap then
			-- moving to next view, move view
			x_pan_off = x_pan_off - self.overlap
		elseif x_pan_off < -self.overlap then
			x_pan_off = x_pan_off + self.overlap
		end
		if y_pan_off > self.overlap then
			y_pan_off = y_pan_off - self.overlap
		elseif y_pan_off < -self.overlap then
			y_pan_off = y_pan_off + self.overlap
		end
		-- we have to calculate again to count into overlap
		new_va.x = Math.roundAwayFromZero(self.visible_area.x+x_pan_off)
		new_va.y = Math.roundAwayFromZero(self.visible_area.y+y_pan_off)
		-- fit new view area into page area
		new_va:offsetWithin(self.page_area, 0, 0)
		-- calculate panning offsets
		local panned_x = new_va.x - self.visible_area.x
		local panned_y = new_va.y - self.visible_area.y
		-- adjust for crazy float point overflow...
		if math.abs(panned_x) < 1 then
			panned_x = 0
		end
		if math.abs(panned_y) < 1 then
			panned_y = 0
		end
		-- singal panning update
		self.view:PanningUpdate(panned_x, panned_y)
		-- update dime area in ReaderView
		if self.show_overlap_enable then
			self.view.dim_area.h = new_va.h - math.abs(panned_y)
			self.view.dim_area.w = new_va.w - math.abs(panned_x)
			if panned_y < 0 then
				self.view.dim_area.y = new_va.y - panned_y
			else
				self.view.dim_area.y = 0
			end
			if panned_x < 0 then
				self.view.dim_area.x = new_va.x - panned_x
			else
				self.view.dim_area.x = 0
			end
		end
		-- update self.visible_area
		self.visible_area = new_va
	end

	return true
end

function ReaderPaging:onRedrawCurrentPage()
	self.ui:handleEvent(Event:new("PageUpdate", self.current_page))
	return true
end

function ReaderPaging:onSetDimensions()
	-- update listening according to new screen dimen
	if Device:isTouchDevice() then
		self:initGesListener()
	end
end

-- wrapper for bounds checking
function ReaderPaging:gotoPage(number, orig)
	--DEBUG.traceback()
	if number == self.current_page or not number then
		return true
	end
	if number > self.number_of_pages
	or number < 1 then
		DEBUG("wrong page number: "..number.."!")
		return false
	end
	DEBUG("going to page number", number)

	-- this is an event to allow other controllers to be aware of this change
	self.ui:handleEvent(Event:new("PageUpdate", number, orig))
	return true
end

function ReaderPaging:onGotoPage(number)
	self:gotoPage(number)
	return true
end

function ReaderPaging:onGotoPercentage(percentage)
	if percentage < 0 then percentage = 0 end
	if percentage > 1 then percentage = 1 end
	self:gotoPage(math.floor(percentage*self.number_of_pages))
	return true
end

return ReaderPaging