ReaderRolling: quicker partial rerenderings with EPUBs

Only available with EPUBs containing 2 or more fragments,
and a file size large enough to ensure a cache file is used.
The idea is simply, on any rendering setting change, to
skip the rerendering of the full book and to defer any
rerendering to the moment we draw a DocFragment, and
render only it.
So, on a setting change, only the fragment containing the
current page will be rerendered, and the new fragments we
may cross while turning pages.
When having done so, KOReader is in a degraded state (the
full page count is incorrect, the ToC is invalid...).
So, a full rerendering is needed, and one will happen
in the background, and when the user is idle, we reload
seamlessly and quickly from the cache file it has made.
ReaderFlipping will show some icons in the top left
corner to let it know at which steps in this procress
we are.

frontend/apps/reader/readerui.lua

@@ -63,7 +63,8 @@ local logger = require("logger")
 local time = require("ui/time")
 local util = require("util")
 local _ = require("gettext")
-local Screen = require("device").screen
+local Input = Device.input
+local Screen = Device.screen
 local T = ffiUtil.template
 
 local ReaderUI = InputContainer:extend{
@@ -109,6 +110,7 @@ function ReaderUI:init()
     -- cap screen refresh on pan to 2 refreshes per second
     local pan_rate = Screen.low_pan_rate and 2.0 or 30.0
 
+    Input:inhibitInput(true) -- Inhibit any past and upcoming input events.
     Device:setIgnoreInput(true) -- Avoid ANRs on Android with unprocessed events.
 
     self.postInitCallback = {}
@@ -479,6 +481,7 @@ function ReaderUI:init()
     self.postReaderCallback = nil
 
     Device:setIgnoreInput(false) -- Allow processing of events (on Android).
+    Input:inhibitInputUntil(0.2)
 
     -- print("Ordered registered gestures:")
     -- for _, tzone in ipairs(self._ordered_touch_zones) do
@@ -562,7 +565,7 @@ end
 --- @note: Will sanely close existing FileManager/ReaderUI instance for you!
 ---        This is the *only* safe way to instantiate a new ReaderUI instance!
 ---        (i.e., don't look at the testsuite, which resorts to all kinds of nasty hacks).
-function ReaderUI:showReader(file, provider)
+function ReaderUI:showReader(file, provider, seamless)
     logger.dbg("show reader ui")
 
     if lfs.attributes(file, "mode") ~= "file" then
@@ -584,21 +587,22 @@ function ReaderUI:showReader(file, provider)
     UIManager:broadcastEvent(Event:new("ShowingReader"))
     provider = provider or DocumentRegistry:getProvider(file)
     if provider.provider then
-        self:showReaderCoroutine(file, provider)
+        self:showReaderCoroutine(file, provider, seamless)
     end
 end
 
-function ReaderUI:showReaderCoroutine(file, provider)
+function ReaderUI:showReaderCoroutine(file, provider, seamless)
     UIManager:show(InfoMessage:new{
         text = T(_("Opening file '%1'."), BD.filepath(file)),
         timeout = 0.0,
+        invisible = seamless,
     })
     -- doShowReader might block for a long time, so force repaint here
     UIManager:forceRePaint()
     UIManager:nextTick(function()
         logger.dbg("creating coroutine for showing reader")
         local co = coroutine.create(function()
-            self:doShowReader(file, provider)
+            self:doShowReader(file, provider, seamless)
         end)
         local ok, err = coroutine.resume(co)
         if err ~= nil or ok == false then
@@ -612,7 +616,7 @@ function ReaderUI:showReaderCoroutine(file, provider)
     end)
 end
 
-function ReaderUI:doShowReader(file, provider)
+function ReaderUI:doShowReader(file, provider, seamless)
     logger.info("opening file", file)
     -- Only keep a single instance running
     if ReaderUI.instance then
@@ -664,7 +668,7 @@ function ReaderUI:doShowReader(file, provider)
         FileManager.instance:onClose()
     end
 
-    UIManager:show(reader, "full")
+    UIManager:show(reader, seamless and "ui" or "full")
 end
 
 -- NOTE: The instance reference used to be stored in a private module variable, hence the getter method.
@@ -832,7 +836,7 @@ function ReaderUI:onReload()
     self:reloadDocument()
 end
 
-function ReaderUI:reloadDocument(after_close_callback)
+function ReaderUI:reloadDocument(after_close_callback, seamless)
     local file = self.document.file
     local provider = getmetatable(self.document).__index
 
@@ -842,6 +846,7 @@ function ReaderUI:reloadDocument(after_close_callback)
 
     self:handleEvent(Event:new("CloseReaderMenu"))
     self:handleEvent(Event:new("CloseConfigMenu"))
+    self:handleEvent(Event:new("PreserveCurrentSession")) -- don't reset statistics' start_current_period
     self.highlight:onClose() -- close highlight dialog if any
     self:onClose(false)
     if after_close_callback then
@@ -849,7 +854,7 @@ function ReaderUI:reloadDocument(after_close_callback)
         after_close_callback(file, provider)
     end
 
-    self:showReader(file, provider)
+    self:showReader(file, provider, seamless)
 end
 
 function ReaderUI:switchDocument(new_file)