add wrapper for u8g2 display driver

src/helpers/ui/U8g2Display.h

@@ -0,0 +1,127 @@
+#pragma once
+
+#include "DisplayDriver.h"
+#include <U8g2lib.h>
+#include <Wire.h>
+
+#ifndef DISPLAY_ADDRESS
+  #define DISPLAY_ADDRESS   0x3C
+#endif
+
+#ifndef OLED_WIDTH
+  #define OLED_WIDTH        72
+#endif
+
+#ifndef OLED_HEIGHT
+  #define OLED_HEIGHT       40
+#endif
+
+class U8g2Display : public DisplayDriver {
+  // U8g2 constructor for SSD1306/SSD1315 72×40 panel — handles all
+  // GDDRAM column/page offsets, SETMULTIPLEX, SETDISPLAYOFFSET internally
+  U8G2_SSD1306_72X40_ER_F_HW_I2C _u8g2;
+  bool _isOn;
+  uint8_t _drawColor;
+
+  // Font metrics for current font (cached on setTextSize)
+  uint8_t _fontAscent;
+  uint8_t _fontHeight;
+
+  void applyFont(int sz) {
+    if (sz >= 2) {
+      _u8g2.setFont(u8g2_font_5x7_mr);      // 5×7 — "large" for this display
+    } else {
+      _u8g2.setFont(u8g2_font_5x7_mr);
+    }
+    _fontAscent = _u8g2.getAscent();
+    _fontHeight = _u8g2.getAscent() - _u8g2.getDescent();
+  }
+
+public:
+  U8g2Display() : DisplayDriver(OLED_WIDTH, OLED_HEIGHT),
+      _u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE),
+      _isOn(false), _drawColor(1), _fontAscent(5), _fontHeight(6) {}
+
+  bool begin() {
+    // Wire must already be initialised by board.begin() before this is called
+    bool ok = _u8g2.begin();
+    if (ok) {
+      _u8g2.setI2CAddress(DISPLAY_ADDRESS * 2);  // U8g2 uses 8-bit address
+      _u8g2.setFontPosTop();     // y coordinate = top of text, not baseline
+      _u8g2.setFontMode(1);      // transparent background
+      applyFont(1);              // default to compact font
+      _isOn = true;
+    }
+    return ok;
+  }
+
+  bool isOn() override { return _isOn; }
+
+  void turnOn() override {
+    _u8g2.setPowerSave(0);
+    _isOn = true;
+  }
+
+  void turnOff() override {
+    _u8g2.setPowerSave(1);
+    _isOn = false;
+  }
+
+  void clear() override {
+    _u8g2.clearBuffer();
+    _u8g2.sendBuffer();
+  }
+
+  void startFrame(Color bkg = DARK) override {
+    _u8g2.clearBuffer();
+    _drawColor = 1;
+    _u8g2.setDrawColor(1);
+    applyFont(1);
+  }
+
+  void setTextSize(int sz) override {
+    applyFont(sz);
+  }
+
+  void setColor(Color c) override {
+    _drawColor = (c != DARK) ? 1 : 0;
+    _u8g2.setDrawColor(_drawColor);
+  }
+
+  void setCursor(int x, int y) override {
+    _cursorX = x;
+    _cursorY = y;
+  }
+
+  void print(const char* str) override {
+    _u8g2.setDrawColor(_drawColor);
+    _u8g2.drawStr(_cursorX, _cursorY, str);
+  }
+
+  void fillRect(int x, int y, int w, int h) override {
+    _u8g2.setDrawColor(_drawColor);
+    _u8g2.drawBox(x, y, w, h);
+  }
+
+  void drawRect(int x, int y, int w, int h) override {
+    _u8g2.setDrawColor(_drawColor);
+    _u8g2.drawFrame(x, y, w, h);
+  }
+
+  void drawXbm(int x, int y, const uint8_t* bits, int w, int h) override {
+    _u8g2.setDrawColor(1);
+    _u8g2.drawXBM(x, y, w, h, bits);
+  }
+
+  uint16_t getTextWidth(const char* str) override {
+    return _u8g2.getStrWidth(str);
+  }
+
+  void endFrame() override {
+    _u8g2.sendBuffer();
+  }
+
+private:
+  int _cursorX = 0;
+  int _cursorY = 0;
+};