fix(reader): preserve KOReader covers in night mode

Counter-invert custom cover pixels before KOReader applies its screen-wide night mode so artwork retains its original colors.

Closes #1885

koreader-plugin/bookorbit.koplugin/bookorbit_board_ui.lua

@@ -16,6 +16,7 @@ data (titles, authors, quotes) may be shortened; pass data = true for those.
 
 local BD = require("ui/bidi")
 local CenterContainer = require("ui/widget/container/centercontainer")
+local Screen = require("device").screen
 local FrameContainer = require("ui/widget/container/framecontainer")
 local Geom = require("ui/geometry")
 local HorizontalGroup = require("ui/widget/horizontalgroup")
@@ -637,6 +638,7 @@ function BoardCover:paintTo(bb, x, y)
         local px_, py_ = x + math.floor((w - img.w) / 2), y + math.floor((h - img.h) / 2)
         bb:blitFrom(img.bb, px_, py_, 0, 0, img.w, img.h)
         if self.dim then bb:lightenRect(x, y, w, h, 0.55) end
+        if Screen.night_mode then bb:invertRect(px_, py_, img.w, img.h) end
         if self.border > 0 then bb:paintBorder(px_, py_, img.w, img.h, self.border, self.border_col or INK.gb) end
         return
     end
@@ -658,6 +660,9 @@ function BoardCover:paintTo(bb, x, y)
     elseif self.lighten then
         bb:lightenRect(dx, dy, dw, dh, self.lighten)
     end
+    if Screen.night_mode then
+        bb:invertRect(dx, dy, dw, dh)
+    end
     if self.border > 0 then
         bb:paintBorder(dx, dy, dw, dh, self.border, self.border_col or INK.gb)
     end

koreader-plugin/spec/bookorbit_board_cover_night_mode_test.lua

@@ -0,0 +1,88 @@
+package.path = "koreader-plugin/bookorbit.koplugin/?.lua;" .. package.path
+
+local widget = {}
+function widget:extend(options)
+    local class = options or {}
+    class.__index = class
+    return setmetatable(class, { __index = self })
+end
+function widget:new(options)
+    return setmetatable(options or {}, { __index = self })
+end
+
+for _, name in ipairs({
+    "ui/geometry", "ui/widget/container/centercontainer", "ui/widget/container/framecontainer",
+    "ui/widget/container/leftcontainer", "ui/widget/container/rightcontainer",
+    "ui/widget/container/widgetcontainer", "ui/widget/horizontalgroup", "ui/widget/horizontalspan",
+    "ui/widget/overlapgroup", "ui/widget/textboxwidget", "ui/widget/textwidget",
+    "ui/widget/verticalgroup", "ui/widget/verticalspan", "ui/widget/widget",
+}) do
+    package.loaded[name] = widget
+end
+
+local native_width, native_height = 100, 150
+local native = {
+    getWidth = function() return native_width end,
+    getHeight = function() return native_height end,
+}
+local scaled = { free = function() end }
+package.loaded["ui/renderimage"] = {
+    renderImageFile = function() return native end,
+    scaleBlitBuffer = function() return scaled end,
+}
+package.loaded["ui/bidi"] = {}
+package.loaded["bookorbit_board_icons"] = {}
+package.loaded["bookorbit_board_metrics"] = {
+    INK = { gb = 32, ge = 224 },
+    px = function(value) return value end,
+}
+
+local Screen = { night_mode = false }
+package.loaded["device"] = { screen = Screen }
+
+local BoardUI = require("bookorbit_board_ui")
+local cover = BoardUI.cover({}, 100, 150, {
+    path = "cover.jpg",
+    border = 1,
+    dim = true,
+})
+
+local calls = {}
+local bb = setmetatable({}, {
+    __index = function(_, name)
+        return function(_, ...)
+            table.insert(calls, { name, ... })
+        end
+    end,
+})
+
+cover:paintTo(bb, 7, 11)
+assert(calls[1][1] == "blitFrom", "the cover image is painted")
+assert(calls[2][1] == "lightenRect", "the offline treatment is painted over the image")
+assert(calls[3][1] == "paintBorder", "day mode leaves the image colors unchanged")
+
+calls = {}
+Screen.night_mode = true
+cover:paintTo(bb, 7, 11)
+assert(calls[1][1] == "blitFrom", "the cover image is painted in night mode")
+assert(calls[2][1] == "lightenRect", "the offline treatment stays before night-mode correction")
+assert(calls[3][1] == "invertRect", "night mode counter-inverts the image before the screen is inverted")
+assert(calls[3][2] == 7 and calls[3][3] == 11 and calls[3][4] == 100 and calls[3][5] == 150,
+    "only the painted image rectangle is counter-inverted")
+assert(calls[4][1] == "paintBorder", "the UI border remains subject to night-mode inversion")
+
+native_width, native_height = 100, 100
+local plated = BoardUI.cover({}, 100, 150, {
+    path = "square-cover.jpg",
+    border = 1,
+    plate = true,
+})
+calls = {}
+plated:paintTo(bb, 7, 11)
+assert(calls[1][1] == "paintRect" and calls[2][1] == "blitFrom", "a nonstandard cover is painted on its plate")
+assert(calls[3][1] == "invertRect", "a plated cover is also corrected in night mode")
+assert(calls[3][2] == 7 and calls[3][3] == 36 and calls[3][4] == 100 and calls[3][5] == 100,
+    "the plate stays inverted with the UI while the image keeps its original colors")
+assert(calls[4][1] == "paintBorder", "the plated image border remains subject to night-mode inversion")
+
+print("bookorbit_board_cover_night_mode_test.lua: passed")

koreader-plugin/spec/bookorbit_board_padding_test.lua

@@ -14,6 +14,7 @@ for _, name in ipairs({
 end
 package.loaded["ui/bidi"] = {}
 package.loaded["ui/renderimage"] = {}
+package.loaded["device"] = { screen = {} }
 package.loaded["bookorbit_board_icons"] = {}
 package.loaded["bookorbit_board_metrics"] = { INK = {}, px = function(n) return n end }