feat: Add FreeInkDisplay functions to work with absolute grayscale luts

libs/display/FreeInkDisplay/include/FreeInkDisplay.h

@@ -123,6 +123,8 @@ class FreeInkDisplay {
   bool supportsBusyGrayscaleStaging() const;
   void prepareGrayscaleTarget();
   bool supportsStripGrayscale() const;
+  // True only when the runtime-selected panel driver accepts absolute LUT plane encoding.
+  bool supportsAbsoluteGrayscale() const;
   // True when displayGrayscaleBase() defers the base activation so the gray
   // planes join it in one waveform (Paper Mono) - see PanelDriver.
   bool combinesGrayscaleBase() const;
@@ -244,6 +246,7 @@ class FreeInkDisplay {
   // EXPERIMENTAL: Windowed update - display only a rectangular region
   void displayWindow(uint16_t x, uint16_t y, uint16_t w, uint16_t h, bool turnOffScreen = false);
   void displayGrayBuffer(bool turnOffScreen = false, const unsigned char* lut = nullptr, bool factoryMode = false);
+  void displayAbsoluteGrayBuffer(bool turnOffScreen = false);
   void displayGrayCalibration(uint16_t customX, uint16_t customY, uint16_t customW, uint16_t customH);
 
   void refreshDisplay(RefreshMode mode = FAST_REFRESH, bool turnOffScreen = false);

libs/display/FreeInkDisplay/src/FreeInkDisplay.cpp

@@ -783,6 +783,19 @@ void FreeInkDisplay::displayGrayBuffer(bool turnOffScreen, const unsigned char*
   _driver->displayGray(_bus, frameBuffer, turnOffScreen, lut, factoryMode);
 }
 
+void FreeInkDisplay::displayAbsoluteGrayBuffer(bool turnOffScreen) {
+#if defined(SSD1677_PROBE_DEBUG) && SSD1677_PROBE_DEBUG
+  Serial.printf("[EPD] displayAbsoluteGrayBuffer\n");
+#endif
+  // Inverted mode deliberately renders a crisp BW page. Writing normal
+  // grayscale planes afterward would partially undo the output inversion.
+  if (_inverted) return;
+  syncPendingAsync();
+  _shadowValid = false;
+  _redRamSynced = false;  // grayscale leaves RED holding a gray plane, not the BW baseline
+  _driver->displayGrayAbsolute(_bus, frameBuffer, turnOffScreen);
+}
+
 void FreeInkDisplay::displayGrayCalibration(uint16_t customX, uint16_t customY, uint16_t customW, uint16_t customH) {
   if (_inverted) return;
   syncPendingAsync();
@@ -859,6 +872,10 @@ bool FreeInkDisplay::supportsStripGrayscale() const {
   return !_inverted && _driver && _driver->supportsStripGrayscale();
 }
 
+bool FreeInkDisplay::supportsAbsoluteGrayscale() const {
+  return !_inverted && _driver && _driver->supportsAbsoluteGrayscale();
+}
+
 bool FreeInkDisplay::combinesGrayscaleBase() const { return _driver && _driver->combinesGrayscaleBase(); }
 
 void FreeInkDisplay::cleanupGrayscaleBuffers(const uint8_t* bwBuffer) {

libs/display/FreeInkDisplay/src/driver/PanelDriver.h

@@ -101,6 +101,11 @@ class PanelDriver {
 
   // --- grayscale (dual-plane LSB/MSB) ---
   virtual bool supportsStripGrayscale() const { return false; }
+
+  // True when this controller accepts absolute selector planes via displayGrayAbsolute()
+  // This is a runtime capability because one firmware image may include several drivers
+  // and driver configurations and select the controller during boot.
+  virtual bool supportsAbsoluteGrayscale() const { return false; }
   // True when displayGrayscaleBase() DEFERS the base activation so the gray
   // planes join it in a single waveform (Paper Mono). Hosts should then route the
   // grayscale base through displayGrayscaleBase() instead of display(): a
@@ -139,6 +144,10 @@ class PanelDriver {
     (void)factoryMode;
     display(bus, fb, nullptr, RefreshMode::Fast, turnOff);
   }
+  virtual void displayGrayAbsolute(EpdBus& bus, const uint8_t* fb, bool turnOff)
+  {
+    displayGray(bus, fb, turnOff, nullptr, false);
+  }
   // Diagnostic four-gray comparison. The full frame is first rendered with
   // the controller's flashing OTP waveform; `custom*` is then rebuilt with the
   // driver's non-flashing grayscale path. Default drivers keep the OTP frame.

libs/display/FreeInkDisplay/src/driver/Ssd1677Driver.cpp

@@ -66,6 +66,8 @@ const Ssd1677Config& ssd1677DefaultConfig() {
       0xC0,  // borderWaveformGray: written explicitly with the external AA LUT (vendor
              // reference stage 2); same value the B/W paths leave in the register, so
              // the wire state is unchanged — just no longer relying on carry-over
+      false, // grayPowerUpFirst
+      true,  // enableAbsoluteLut
   };
   return cfg;
 }
@@ -635,6 +637,11 @@ void Ssd1677Driver::displayGray(EpdBus& bus, const uint8_t* fb, bool turnOff, co
   setCustomLut(bus, false, nullptr);
 }
 
+void Ssd1677Driver::displayGrayAbsolute(EpdBus& bus, const uint8_t* fb, bool turnOff)
+{
+  displayGray(bus, fb, turnOff, lut_factory_quality, true);
+}
+
 void Ssd1677Driver::cleanupGrayscaleBuffers(EpdBus& bus, const uint8_t* bw) {
   if (!bw) return;
   setRamArea(bus, 0, 0, _w, _h);

libs/display/FreeInkDisplay/src/driver/Ssd1677Driver.h

@@ -53,6 +53,7 @@ struct Ssd1677Config {
   // collapsing toward B/W). The X4 keeps the panel powered between fast
   // refreshes, so it never needs this and keeps stock behavior.
   bool grayPowerUpFirst = false;
+  bool enableAbsoluteLut = false;
 };
 
 // Standard config (Xteink X4 / GDEQ0426T82). Panel mounting (mirror/180°) is NOT
@@ -85,11 +86,13 @@ class Ssd1677Driver : public PanelDriver {
   void seedPreviousFrame(EpdBus& bus, const uint8_t* buf) override;
 
   bool supportsStripGrayscale() const override { return true; }
+  bool supportsAbsoluteGrayscale() const override { return _cfg.enableAbsoluteLut; }
   void copyGrayscaleLsb(EpdBus& bus, const uint8_t* lsb) override;
   void copyGrayscaleMsb(EpdBus& bus, const uint8_t* msb) override;
   void writeGrayscalePlaneStrip(EpdBus& bus, GrayPlane plane, const uint8_t* rows, uint16_t yStart,
                                 uint16_t numRows) override;
   void displayGray(EpdBus& bus, const uint8_t* fb, bool turnOff, const unsigned char* lut, bool factoryMode) override;
+  void displayGrayAbsolute(EpdBus& bus, const uint8_t* fb, bool turnOff) override;
   void cleanupGrayscaleBuffers(EpdBus& bus, const uint8_t* bw) override;
 
   // No grayscaleRevert override: stock parity — the OEM firmware has no revert