feat: implement sunlight fading fix (PR #603)

Add user-toggleable setting to turn off display between refreshes,
which helps mitigate the sunlight fading issue on e-ink displays.

Changes:
- Add turnOffScreen parameter to HalDisplay methods
- Add fadingFix member and setFadingFix() to GfxRenderer
- Add fadingFix setting to CrossPointSettings with persistence
- Add "Sunlight Fading Fix" toggle in Display settings
- Update SDK submodule with turnOffScreen support

lib/GfxRenderer/GfxRenderer.cpp

@@ -531,7 +531,9 @@ void GfxRenderer::invertScreen() const {
   }
 }
 
-void GfxRenderer::displayBuffer(const HalDisplay::RefreshMode refreshMode) const { display.displayBuffer(refreshMode); }
+void GfxRenderer::displayBuffer(const HalDisplay::RefreshMode refreshMode) const {
+  display.displayBuffer(refreshMode, fadingFix);
+}
 
 std::string GfxRenderer::truncatedText(const int fontId, const char* text, const int maxWidth,
                                        const EpdFontFamily::Style style) const {
@@ -910,7 +912,7 @@ void GfxRenderer::copyGrayscaleLsbBuffers() const { display.copyGrayscaleLsbBuff
 
 void GfxRenderer::copyGrayscaleMsbBuffers() const { display.copyGrayscaleMsbBuffers(display.getFrameBuffer()); }
 
-void GfxRenderer::displayGrayBuffer() const { display.displayGrayBuffer(); }
+void GfxRenderer::displayGrayBuffer() const { display.displayGrayBuffer(fadingFix); }
 
 void GfxRenderer::freeBwBufferChunks() {
   for (auto& bwBufferChunk : bwBufferChunks) {

lib/GfxRenderer/GfxRenderer.h

@@ -37,6 +37,7 @@ class GfxRenderer {
   HalDisplay& display;
   RenderMode renderMode;
   Orientation orientation;
+  bool fadingFix = false;     // Sunlight fading fix - turn off screen after refresh
   int bezelCompensation = 0;  // Pixels to add for bezel defect compensation
   int bezelEdge = 0;          // Which physical edge (0=bottom, 1=top, 2=left, 3=right in portrait)
   uint8_t* bwBufferChunks[BW_BUFFER_NUM_CHUNKS] = {nullptr};
@@ -76,6 +77,9 @@ class GfxRenderer {
   void setOrientation(const Orientation o) { orientation = o; }
   Orientation getOrientation() const { return orientation; }
 
+  // Fading fix control
+  void setFadingFix(const bool enabled) { fadingFix = enabled; }
+
   // Screen ops
   int getScreenWidth() const;
   int getScreenHeight() const;

lib/hal/HalDisplay.cpp

@@ -28,7 +28,9 @@ EInkDisplay::RefreshMode convertRefreshMode(HalDisplay::RefreshMode mode) {
   }
 }
 
-void HalDisplay::displayBuffer(HalDisplay::RefreshMode mode) { einkDisplay.displayBuffer(convertRefreshMode(mode)); }
+void HalDisplay::displayBuffer(HalDisplay::RefreshMode mode, bool turnOffScreen) {
+  einkDisplay.displayBuffer(convertRefreshMode(mode), turnOffScreen);
+}
 
 void HalDisplay::refreshDisplay(HalDisplay::RefreshMode mode, bool turnOffScreen) {
   einkDisplay.refreshDisplay(convertRefreshMode(mode), turnOffScreen);
@@ -48,4 +50,4 @@ void HalDisplay::copyGrayscaleMsbBuffers(const uint8_t* msbBuffer) { einkDisplay
 
 void HalDisplay::cleanupGrayscaleBuffers(const uint8_t* bwBuffer) { einkDisplay.cleanupGrayscaleBuffers(bwBuffer); }
 
-void HalDisplay::displayGrayBuffer() { einkDisplay.displayGrayBuffer(); }
+void HalDisplay::displayGrayBuffer(bool turnOffScreen) { einkDisplay.displayGrayBuffer(turnOffScreen); }

lib/hal/HalDisplay.h

@@ -31,7 +31,7 @@ class HalDisplay {
   void drawImage(const uint8_t* imageData, uint16_t x, uint16_t y, uint16_t w, uint16_t h,
                  bool fromProgmem = false) const;
 
-  void displayBuffer(RefreshMode mode = RefreshMode::FAST_REFRESH);
+  void displayBuffer(RefreshMode mode = RefreshMode::FAST_REFRESH, bool turnOffScreen = false);
   void refreshDisplay(RefreshMode mode = RefreshMode::FAST_REFRESH, bool turnOffScreen = false);
 
   // Power management
@@ -45,7 +45,7 @@ class HalDisplay {
   void copyGrayscaleMsbBuffers(const uint8_t* msbBuffer);
   void cleanupGrayscaleBuffers(const uint8_t* bwBuffer);
 
-  void displayGrayBuffer();
+  void displayGrayBuffer(bool turnOffScreen = false);
 
  private:
   EInkDisplay einkDisplay;

open-x4-sdk

@@ -1 +1 @@
-Subproject commit dede09001c4c7bc96bd3616716cdf80913f57658
+Subproject commit be6ba1b62b1262929cded6ccdae774a098d33010

src/CrossPointSettings.cpp

@@ -23,7 +23,7 @@ void readAndValidate(FsFile& file, uint8_t& member, const uint8_t maxValue) {
 namespace {
 constexpr uint8_t SETTINGS_FILE_VERSION = 1;
 // Increment this when adding new persisted settings fields
-constexpr uint8_t SETTINGS_COUNT = 29;  // 28 + bezelCompensationEdge
+constexpr uint8_t SETTINGS_COUNT = 30;  // 29 + fadingFix
 constexpr char SETTINGS_FILE[] = "/.crosspoint/settings.bin";
 }  // namespace
 
@@ -72,6 +72,8 @@ bool CrossPointSettings::saveToFile() const {
   serialization::writePod(outputFile, bezelCompensation);
   // Which physical edge needs bezel compensation
   serialization::writePod(outputFile, bezelCompensationEdge);
+  // Sunlight fading fix
+  serialization::writePod(outputFile, fadingFix);
   // New fields added at end for backward compatibility
   outputFile.close();
 
@@ -182,6 +184,9 @@ bool CrossPointSettings::loadFromFile() {
     // Which physical edge needs bezel compensation
     readAndValidate(inputFile, bezelCompensationEdge, BEZEL_EDGE_COUNT);
     if (++settingsRead >= fileSettingsCount) break;
+    // Sunlight fading fix
+    serialization::readPod(inputFile, fadingFix);
+    if (++settingsRead >= fileSettingsCount) break;
     // New fields added at end for backward compatibility
   } while (false);
 

src/CrossPointSettings.h

@@ -144,6 +144,8 @@ class CrossPointSettings {
   uint8_t hideBatteryPercentage = HIDE_NEVER;
   // Long-press chapter skip on side buttons
   uint8_t longPressChapterSkip = 1;
+  // Sunlight fading compensation (0 = off, 1 = on)
+  uint8_t fadingFix = 0;
   // System-wide display contrast (0 = normal, 1 = high)
   uint8_t displayContrast = 0;
   // Bezel compensation - extra margin for physical screen edge defects (0-10px)

src/activities/settings/SettingsActivity.cpp

@@ -15,7 +15,7 @@ namespace {
 // Visibility condition for bezel edge setting (only show when compensation > 0)
 bool isBezelCompensationEnabled() { return SETTINGS.bezelCompensation > 0; }
 
-constexpr int displaySettingsCount = 9;
+constexpr int displaySettingsCount = 10;
 const SettingInfo displaySettings[displaySettingsCount] = {
     // Should match with SLEEP_SCREEN_MODE
     SettingInfo::Enum("Sleep Screen", &CrossPointSettings::sleepScreen, {"Dark", "Light", "Custom", "Cover", "None"}),
@@ -28,6 +28,7 @@ const SettingInfo displaySettings[displaySettingsCount] = {
     SettingInfo::Enum("Hide Battery %", &CrossPointSettings::hideBatteryPercentage, {"Never", "In Reader", "Always"}),
     SettingInfo::Enum("Refresh Frequency", &CrossPointSettings::refreshFrequency,
                       {"1 page", "5 pages", "10 pages", "15 pages", "30 pages"}),
+    SettingInfo::Enum("Sunlight Fading Fix", &CrossPointSettings::fadingFix, {"OFF", "ON"}),
     SettingInfo::Value("Bezel Compensation", &CrossPointSettings::bezelCompensation, {0, 10, 1}),
     SettingInfo::Enum("Bezel Edge", &CrossPointSettings::bezelCompensationEdge, {"Bottom", "Top", "Left", "Right"},
                       isBezelCompensationEnabled)};

src/main.cpp

@@ -524,6 +524,8 @@ void loop() {
 
   gpio.update();
 
+  renderer.setFadingFix(SETTINGS.fadingFix);
+
   if (Serial && millis() - lastMemPrint >= 10000) {
     // Basic heap info
     Serial.printf("[%lu] [MEM] Free: %d bytes, Total: %d bytes, Min Free: %d bytes\n", millis(), ESP.getFreeHeap(),