KOptOptions: Allow toggling SW dithering

Fix #8748

frontend/apps/reader/modules/readerview.lua

@@ -221,7 +221,7 @@ function ReaderView:paintTo(bb, x, y)
     self.dialog.dithered = nil
     -- For KOpt, let the user choose.
     if self.ui.document.info.has_pages then
-        -- Also enforce dithering in PicDocument
+        -- Also enforce HW dithering in PicDocument
         if self.ui.document.is_pic or self.document.configurable.hw_dithering == 1 then
             self.dialog.dithered = true
         end

frontend/dispatcher.lua

@@ -190,6 +190,7 @@ local settingsList = {
     kopt_contrast = {category="absolutenumber", paging=true},
     kopt_page_opt = {category="configurable", paging=true},
     kopt_hw_dithering = {category="configurable", paging=true, condition=Device:hasEinkScreen() and Device:canHWDither()},
+    kopt_sw_dithering = {category="configurable", paging=true, condition=Device:hasEinkScreen() and Device.screen.fb_bpp == 8},
     kopt_quality = {category="configurable", paging=true},
     kopt_doc_language = {category="string", paging=true},
     kopt_forced_ocr = {category="configurable", paging=true},
@@ -355,6 +356,7 @@ local dispatcher_menu_order = {
     "kopt_contrast",
     "kopt_page_opt",
     "kopt_hw_dithering",
+    "kopt_sw_dithering",
     "kopt_quality",
 
     "kopt_doc_language",

frontend/document/canvascontext.lua

@@ -51,6 +51,10 @@ function CanvasContext:init(device)
         self.is_bgr = true
         Mupdf.bgr = true
     end
+
+    self.hasEinkScreen = device.hasEinkScreen
+    self.canHWDither = device.canHWDither
+    self.fb_bpp = device.screen.fb_bpp
 end
 
 

frontend/document/document.lua

@@ -495,11 +495,21 @@ Draw page content to blitbuffer.
 --]]
 function Document:drawPage(target, x, y, rect, pageno, zoom, rotation, gamma, render_mode)
     local tile = self:renderPage(pageno, rect, zoom, rotation, gamma, render_mode)
-    target:blitFrom(tile.bb,
-        x, y,
-        rect.x - tile.excerpt.x,
-        rect.y - tile.excerpt.y,
-        rect.w, rect.h)
+    -- Enable SW dithering if requested (only available in koptoptions)
+    -- Much Like ReaderView, also enforce SW dithering in PicDocument if the device can't do HW dithering...
+    if (self.is_pic and CanvasContext:hasEinkScreen() and not CanvasContext:canHWDither() and CanvasContext.fb_bpp == 8) or (self.configurable.sw_dithering and self.configurable.sw_dithering == 1) then
+        target:ditherblitFrom(tile.bb,
+            x, y,
+            rect.x - tile.excerpt.x,
+            rect.y - tile.excerpt.y,
+            rect.w, rect.h)
+    else
+        target:blitFrom(tile.bb,
+            x, y,
+            rect.x - tile.excerpt.x,
+            rect.y - tile.excerpt.y,
+            rect.w, rect.h)
+    end
 end
 
 function Document:getDrawnImagesStatistics()

frontend/ui/data/koptoptions.lua

@@ -497,14 +497,25 @@ This can also be used to remove some gray background or to convert a grayscale o
             },
             {
                 name = "hw_dithering",
-                name_text = _("Dithering"),
+                name_text = _("HW Dithering"),
                 toggle = {_("off"), _("on")},
                 values = {0, 1},
                 default_value = 0,
                 advanced = true,
                 show = Device:hasEinkScreen() and Device:canHWDither(),
                 name_text_hold_callback = optionsutil.showValues,
-                help_text = _([[Enable Hardware dithering.]]),
+                help_text = _([[Enable hardware dithering.]]),
+            },
+            {
+                name = "sw_dithering",
+                name_text = _("SW Dithering"),
+                toggle = {_("off"), _("on")},
+                values = {0, 1},
+                default_value = 0,
+                advanced = true,
+                show = Device:hasEinkScreen() and Device.screen.fb_bpp == 8,
+                name_text_hold_callback = optionsutil.showValues,
+                help_text = _([[Enable software dithering.]]),
             },
             {
                 name = "quality",