Fix a few logic holes in dithering mode selection (#6419)

* Allow switching to SW dithering on a HW-capable device without that being lost on boot (and, worse, left in an undithered state).
* Make sure the automagic toggles between HW/SW in the Dev menu are properly saved.

base

@@ -1 +1 @@
-Subproject commit fac6e7c85250b138a5603f54fc3427d62c141420
+Subproject commit ac608dec4033f3eef8bcdd8c4861dc4efc0abaab

frontend/apps/filemanager/filemanagermenu.lua

@@ -356,11 +356,12 @@ function FileManagerMenu:setUpdateItemTable()
                 return not Device.screen.hw_dithering
             end,
             callback = function()
-                G_reader_settings:flipNilOrFalse("dev_no_hw_dither")
                 Device.screen:toggleHWDithering()
+                G_reader_settings:saveSetting("dev_no_hw_dither", not Device.screen.hw_dithering)
                 -- Make sure SW dithering gets disabled when we enable HW dithering
                 if Device.screen.hw_dithering and Device.screen.sw_dithering then
-                    Device.screen:toggleSWDithering()
+                    G_reader_settings:saveSetting("dev_no_sw_dither", true)
+                    Device.screen:toggleSWDithering(false)
                 end
                 UIManager:setDirty("all", "full")
             end,
@@ -376,11 +377,12 @@ function FileManagerMenu:setUpdateItemTable()
                 return not Device.screen.sw_dithering
             end,
             callback = function()
-                G_reader_settings:flipNilOrFalse("dev_no_sw_dither")
                 Device.screen:toggleSWDithering()
+                G_reader_settings:saveSetting("dev_no_sw_dither", not Device.screen.sw_dithering)
                 -- Make sure HW dithering gets disabled when we enable SW dithering
                 if Device.screen.hw_dithering and Device.screen.sw_dithering then
-                    Device.screen:toggleHWDithering()
+                    G_reader_settings:saveSetting("dev_no_hw_dither", true)
+                    Device.screen:toggleHWDithering(false)
                 end
                 UIManager:setDirty("all", "full")
             end,

reader.lua

@@ -130,10 +130,15 @@ end
 if Device:hasEinkScreen() then
     Device.screen:setupDithering()
     if Device.screen.hw_dithering and G_reader_settings:isTrue("dev_no_hw_dither") then
-        Device.screen:toggleHWDithering()
+        Device.screen:toggleHWDithering(false)
     end
     if Device.screen.sw_dithering and G_reader_settings:isTrue("dev_no_sw_dither") then
-        Device.screen:toggleSWDithering()
+        Device.screen:toggleSWDithering(false)
+    end
+    -- NOTE: If device can HW dither (i.e., after setupDithering(), hw_dithering is true, but sw_dithering is false),
+    --       but HW dither is explicitly disabled, and SW dither enabled, don't leave SW dither disabled (i.e., re-enable sw_dithering)!
+    if Device:canHWDither() and G_reader_settings:isTrue("dev_no_hw_dither") and G_reader_settings:nilOrFalse("dev_no_sw_dither") then
+        Device.screen:toggleSWDithering(true)
     end
 end