Minor flash tweaks after #6528 (#6540)

* Boundaries are now detected both when paging forward and backward.

Fixes potential false-negatives in the chapter boundary heuristic code, as mentioned in https://github.com/koreader/koreader/pull/6528#issuecomment-678610188 ;).

* Tweaked ReaderFooter to not repaint ReaderUI when it's unnecessary. (toggling/cycling it on a page with significant image content would flash the full screen).

* Only flash the first time a page w/ significant image content is shown. (Menus, among other things, could otherwise re-trip the flash).

frontend/apps/reader/modules/readerfooter.lua

@@ -1766,10 +1766,36 @@ function ReaderFooter:_updateFooterText(force_repaint, force_recompute)
     -- NOTE: That's assuming using "fast" for pans was a good idea, which, it turned out, not so much ;).
     -- NOTE: We skip repaints on page turns/pos update, as that's redundant (and slow).
     if force_repaint then
-        -- NOTE: We need to repaint everything when toggling the progress bar, for some reason.
-        UIManager:setDirty(self.view.dialog, function()
-            return "ui", self.footer_content.dimen
-        end)
+        -- NOTE: Getting the dimensions of the widget is impossible without having drawn it first,
+        --       so, we'll fudge it if need be...
+        local refresh_dim = self.footer_content.dimen
+        -- No content yet...
+        if not refresh_dim then
+            -- So, instead, compute self.footer_content's height ourselves: i.e., self.vertical_frame + self.bottom_padding...
+            refresh_dim = self.dimen
+            if self.view.footer_visible then
+                refresh_dim.h = self.vertical_frame:getSize().h + self.bottom_padding
+            else
+                -- When going invisible, the text is no longer visible, so the frame's height is off by self.height
+                refresh_dim.h = self.vertical_frame:getSize().h + self.height + self.bottom_padding
+            end
+            refresh_dim.y = self._saved_screen_height - refresh_dim.h
+        end
+        -- If we're making the footer visible (or it already is), we don't need to repaint ReaderUI behind it
+        if self.view.footer_visible then
+            -- 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)
+        else
+            UIManager:setDirty(self.view.dialog, function()
+                return "ui", refresh_dim
+            end)
+        end
     end
 end
 

frontend/apps/reader/modules/readertoc.lua

@@ -59,23 +59,29 @@ function ReaderToc:onUpdateToc()
 end
 
 function ReaderToc:onPageUpdate(pageno)
-    self.pageno = pageno
     if UIManager.FULL_REFRESH_COUNT == -1 or G_reader_settings:isTrue("refresh_on_chapter_boundaries") then
         local flash_on_second = G_reader_settings:nilOrFalse("no_refresh_on_second_chapter_page")
-        if self:isChapterEnd(pageno, 0) then
-            self.chapter_refresh = true
-        elseif self.chapter_refresh and self:isChapterStart(pageno, 0) then
-            UIManager:setDirty(nil, "full")
-            if not flash_on_second then
-                self.chapter_refresh = false
+        local paging_forward, paging_backward
+        if flash_on_second then
+            if self.pageno then
+                if pageno > self.pageno then
+                    paging_forward = true
+                elseif pageno < self.pageno then
+                    paging_backward = true
+                end
             end
-        elseif self.chapter_refresh and self:isChapterSecondPage(pageno, 0) then
+        end
+
+        if paging_backward and self:isChapterEnd(pageno, 0) then
+            UIManager:setDirty(nil, "full")
+        elseif self:isChapterStart(pageno, 0) then
+            UIManager:setDirty(nil, "full")
+        elseif paging_forward and self:isChapterSecondPage(pageno, 0) then
             UIManager:setDirty(nil, "full")
-            self.chapter_refresh = false
-        else
-            self.chapter_refresh = false
         end
     end
+
+    self.pageno = pageno
 end
 
 function ReaderToc:onPosUpdate(pos, pageno)

frontend/apps/reader/modules/readerview.lua

@@ -223,9 +223,12 @@ function ReaderView:paintTo(bb, x, y)
         -- With some nil guards because this may not be implemented in every engine ;).
         if img_count and img_count > 0 and img_coverage and img_coverage >= 0.075 then
             self.dialog.dithered = true
-            -- Request a flashing update while we're at it
-            UIManager:setDirty(nil, "full")
+            -- Request a flashing update while we're at it, but only if it's the first time we're painting it
+            if self.state.drawn == false then
+                UIManager:setDirty(nil, "full")
+            end
         end
+        self.state.drawn = true
     end
 end
 
@@ -760,6 +763,7 @@ end
 
 function ReaderView:onPageUpdate(new_page_no)
     self.state.page = new_page_no
+    self.state.drawn = false
     self:recalculate()
     self.highlight.temp = {}
     self:checkAutoSaveSettings()