ReaderRolling: avoid ANR on Android when (re)rendering. (#8501)

Wrap document opening and re-renderings (which can block
the app for some time) with setIgnoreInput() to avoid ANR
on Android.
Any setting update that could possibly cause a re-rendering
should send the UpdatePos event, to ensure the re-rendering
happens in ReaderRolling:onUpdatePos() where precautions
are taken to avoid ANR.

frontend/apps/reader/modules/readerrolling.lua

@@ -867,16 +867,24 @@ function ReaderRolling:onUpdatePos()
         -- we have set above) to avoid multiple refreshes.
         return true
     end
+
+    UIManager:discardEvents(math.huge) -- Discard any past and upcoming input events for the next hour.
+    Device:setIgnoreInput(true) -- Avoid ANRs on Android with unprocessed events.
+
     -- Calling this now ensures the re-rendering is done by crengine
     -- so updatePos() has good info and can reposition
     -- the previous xpointer accurately:
     self.ui.document:getCurrentPos()
+
     -- Otherwise, _readMetadata() would do that, but the positioning
     -- would not work as expected, for some reason (it worked
     -- previously because of some bad setDirty() in ConfigDialog widgets
     -- that were triggering a full repaint of crengine (so, the needed
     -- rerendering) before updatePos() is called.
     self:updatePos()
+
+    Device:setIgnoreInput(false) -- Allow processing of events (on Android).
+    UIManager:discardEvents(true) -- Discard events, which might have occured (double tap).
 end
 
 function ReaderRolling:updatePos()

frontend/apps/reader/readerui.lua

@@ -106,6 +106,8 @@ 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
 
+    Device:setIgnoreInput(true) -- Avoid ANRs on Android with unprocessed events.
+
     self.postInitCallback = {}
     self.postReaderCallback = {}
     -- if we are not the top level dialog ourselves, it must be given in the table
@@ -457,6 +459,8 @@ function ReaderUI:init()
     end
     self.postReaderCallback = nil
 
+    Device:setIgnoreInput(false) -- Allow processing of events (on Android).
+
     -- print("Ordered registered gestures:")
     -- for _, tzone in ipairs(self._ordered_touch_zones) do
     --     print("  "..tzone.def.id)

frontend/device/android/device.lua

@@ -311,6 +311,7 @@ function Device:performHapticFeedback(type)
 end
 
 function Device:setIgnoreInput(enable)
+    logger.dbg("android.setIgnoreInput", enable)
     android.setIgnoreInput(enable)
 end