Prevent automatic footer refreshes from drawing the footer on top of stuff that isn't ReaderUI (#6648)

* Prevent refreshing the footer automatically where it doesn't make sense to.

Issue exposed by #6540
Fix #6616

frontend/apps/reader/modules/readerconfig.lua

@@ -81,6 +81,7 @@ end
 
 function ReaderConfig:onShowConfigMenu()
     self.config_dialog = ConfigDialog:new{
+        covers_footer = true, -- hint for UIManager:repaintReaderFooter
         dimen = self.dimen:copy(),
         document = self.document,
         ui = self.ui,

frontend/apps/reader/modules/readerfooter.lua

@@ -1795,11 +1795,13 @@ function ReaderFooter:_updateFooterText(force_repaint, force_recompute)
             -- Unfortunately, it's not a modal (we never show() it), so it's not in the window stack,
             -- instead, it's baked inside ReaderUI, so it gets slightly trickier...
             -- NOTE: self.view.footer -> self ;).
-            UIManager:setDirty(self.view.footer, function()
-                return "ui", refresh_dim
-            end)
-            -- c.f., ReaderView:paintTo()
-            UIManager:widgetRepaint(self.view.footer, 0, 0)
+            if UIManager:repaintReaderFooter(self.view.footer) then
+                -- NOTE: repaintReaderFooter will sometimes choose *not* to repaint, in which case,
+                --       we don't want to generate a bogus setDirty call ;).
+                UIManager:setDirty(self.view.footer, function()
+                    return "ui", refresh_dim
+                end)
+            end
         else
             UIManager:setDirty(self.view.dialog, function()
                 return "ui", refresh_dim
@@ -2005,6 +2007,16 @@ function ReaderFooter:onSuspend()
     end
 end
 
+-- We want to be able to disable auto_refresh_time when displaying *some* non-fullscreen widgets on top of ReaderUI,
+-- otherwise it'll happily keep on ticking and drawing on top of stuff it ought not to... (#6616)
+--- @note: If the widget actually makes it to UIManager's window stack (i.e., it's passed to UIManager:show()),
+---        it's generally simpler to set covers_footer when initializing the Widget object.
+-- Since these Events are not currently in use, comment the handlers out ;).
+--[[
+ReaderFooter.onDisableFooterAutoRefresh = ReaderFooter.onSuspend
+ReaderFooter.onRestoreFooterAutoRefresh = ReaderFooter.onResume
+--]]
+
 function ReaderFooter:onFrontlightStateChanged()
     if self.settings.frontlight then
         self:onUpdateFooter(true)

frontend/apps/reader/modules/readerlink.lua

@@ -1263,6 +1263,7 @@ function ReaderLink:showAsFootnotePopup(link, neglect_current_location)
     local FootnoteWidget = require("ui/widget/footnotewidget")
     local popup
     popup = FootnoteWidget:new{
+        covers_footer = true, -- hint for UIManager:repaintReaderFooter
         html = html,
         doc_font_size = Screen:scaleBySize(self.ui.font.font_size),
         doc_margins = self.ui.document:getPageMargins(),

frontend/ui/uimanager.lua

@@ -1045,6 +1045,16 @@ function UIManager:_repaint()
         end
     end
 
+    -- Show IDs of covered widgets when debugging
+    --[[
+    if start_idx > 1 then
+        for i = 1, start_idx-1 do
+            local widget = self._window_stack[i]
+            logger.dbg("NOT painting widget:", widget.widget.name or widget.widget.id or tostring(widget))
+        end
+    end
+    --]]
+
     for i = start_idx, #self._window_stack do
         local widget = self._window_stack[i]
         -- paint if current widget or any widget underneath is dirty
@@ -1141,6 +1151,43 @@ function UIManager:widgetRepaint(widget, x, y)
     widget:paintTo(Screen.bb, x, y)
 end
 
+-- Now, this one is basically widgetRepaint, but tailored for a very,
+-- very specific use-case related to ReaderFooter:setupAutoRefreshTime
+-- (c.f., #6648)
+function UIManager:repaintReaderFooter(readerfooter_widget)
+    if not readerfooter_widget then return false end
+
+    -- Don't repaint if there's another widget than ReaderUI flagged as covers_fullscreen being shown,
+    -- or if a non-fullscreen widget is flagged as covers_footer.
+    -- This isn't particularly pretty, but, oh, well (#6616).
+    local skip_repaint = false
+    -- c.f., UIManager:_repaint
+    for i = #self._window_stack, 1, -1 do
+        local widget = self._window_stack[i].widget
+        if widget.covers_fullscreen then
+            if widget.name and widget.name == "ReaderUI" then  -- luacheck: ignore
+                -- NOP (i.e., continue)
+            else
+                skip_repaint = true
+                logger.dbg("Skipping ReaderFooter repaint, because something covers ReaderUI")
+                break
+            end
+        elseif widget.covers_footer then
+            skip_repaint = true
+            logger.dbg("Skipping ReaderFooter repaint, because something covers ReaderFooter")
+            break
+        end
+    end
+    if skip_repaint then return false end
+
+    logger.dbg("Explicit ReaderFooter repaint:", readerfooter_widget.name or readerfooter_widget.id or tostring(readerfooter_widget))
+    -- c.f., ReaderView:paintTo()
+    readerfooter_widget:paintTo(Screen.bb, 0, 0)
+
+    -- Inform the caller that we did, in fact, repaint it.
+    return true
+end
+
 function UIManager:setInputTimeout(timeout)
     self.INPUT_TIMEOUT = timeout or 200*1000
 end
@@ -1178,6 +1225,8 @@ function UIManager:handleInput()
     repeat
         wait_until, now = self:_checkTasks()
         --dbg("---------------------------------------------------")
+        --dbg("wait_until", wait_until)
+        --dbg("now", now)
         --dbg("exec stack", self._task_queue)
         --dbg("window stack", self._window_stack)
         --dbg("dirty stack", self._dirty)