refactor(eink): centralise scale() helper, hoist out of Lemon hot loop

Per-char recomputation of (width() >= height() ? 2 : 1) in drawLemonChar
and lemonXAdvance is now passed in by the caller. print() and
getTextWidth() compute scale() once and feed it to every glyph. All
other callers in the file route through the helper for consistency.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/helpers/ui/GxEPDDisplay.cpp

@@ -51,8 +51,7 @@ uint32_t GxEPDDisplay::decodeUtf8(const uint8_t*& p) {
 // y is the GFX baseline (display.getCursorY()), which equals original_y + 8*sc.
 // Pixels are placed at y + yo*sc + row*sc — identical to how GFX would render
 // a scaled GFX font, but bypassing GFX so multi-byte UTF-8 is decoded correctly.
-int16_t GxEPDDisplay::drawLemonChar(int16_t x, int16_t y, uint32_t cp) {
-  int sc = (width() >= height()) ? 2 : 1;
+int16_t GxEPDDisplay::drawLemonChar(int16_t x, int16_t y, uint32_t cp, int sc) {
   for (uint8_t i = 0; i < lemonIconCount; i++) {
     if (pgm_read_dword(&lemonIconCPs[i]) == cp) {
       const GFXglyph* g = &lemonIconGlyphs[i];
@@ -95,11 +94,11 @@ int16_t GxEPDDisplay::drawLemonChar(int16_t x, int16_t y, uint32_t cp) {
   return x + xa * sc;
 }
 
-uint8_t GxEPDDisplay::lemonXAdvance(uint32_t cp) {
+uint8_t GxEPDDisplay::lemonXAdvance(uint32_t cp, int sc) {
   uint8_t xa;
   if (cp < Lemon.first || cp > Lemon.last) xa = 6;
   else xa = pgm_read_byte(&lemonGlyphs[cp - Lemon.first].xAdvance);
-  return xa * ((width() >= height()) ? 2 : 1);
+  return xa * sc;
 }
 
 bool GxEPDDisplay::begin() {
@@ -152,7 +151,7 @@ void GxEPDDisplay::startFrame(Color bkg) {
   display.fillScreen(GxEPD_WHITE);
   display.setTextColor(_curr_color = GxEPD_BLACK);
   _text_sz = 1;
-  int sc = (width() >= height()) ? 2 : 1;
+  int sc = scale();
   display.setFont(_use_lemon ? &Lemon : NULL);
   display.setTextSize(sc);
   display_crc.reset();
@@ -165,7 +164,7 @@ void GxEPDDisplay::setTextSize(int sz) {
   // Size 1 scales with orientation: 1× in portrait (≈OLED width), 2× in landscape.
   // Size 2 always uses 2× built-in (12×16) — fixed because layout Y-positions are hardcoded.
   // Size 3 always uses FreeSans18pt for large headings.
-  int sc = (width() >= height()) ? 2 : 1;
+  int sc = scale();
   switch (sz) {
     case 3:
       display.setFont(&FreeSans18pt7b);
@@ -173,7 +172,7 @@ void GxEPDDisplay::setTextSize(int sz) {
       break;
     case 2:
       display.setFont(NULL);
-      display.setTextSize((width() >= height()) ? 4 : 2);
+      display.setTextSize(scale() * 2);
       break;
     default:
       display.setFont(_use_lemon ? &Lemon : NULL);
@@ -197,7 +196,7 @@ void GxEPDDisplay::setCursor(int x, int y) {
   display_crc.update<int>(y);
   // Offset y by the font ascender: callers pass top-of-cell y, GFX fonts
   // expect baseline y. Without this, text would be clipped at the top.
-  int sc = (width() >= height()) ? 2 : 1;
+  int sc = scale();
   display.setCursor(x, y + fontAscender(_text_sz, _use_lemon, sc));
 }
 
@@ -207,17 +206,17 @@ void GxEPDDisplay::print(const char* str) {
   if (_use_lemon && _text_sz == 1) {
     int16_t cx = display.getCursorX();
     int16_t cy = display.getCursorY();
-    int sc = (width() >= height()) ? 2 : 1;
+    const int sc = scale();
     const uint8_t* p = (const uint8_t*)str;
     while (*p) {
       uint32_t cp = decodeUtf8(p);
       if (cp == '\n') { cy += Lemon.yAdvance * sc; cx = 0; }
-      else            { cx = drawLemonChar(cx, cy, cp); }
+      else            { cx = drawLemonChar(cx, cy, cp, sc); }
     }
     display.setCursor(cx, cy);
     return;
   }
-  int sc = (width() >= height()) ? 2 : 1;
+  int sc = scale();
   for (const char* p = str; *p; p++) {
     if ((uint8_t)*p == 0xDB) {
       int cx = display.getCursorX();
@@ -245,7 +244,7 @@ void GxEPDDisplay::drawRect(int x, int y, int w, int h) {
   display_crc.update<int>(w);
   display_crc.update<int>(h);
   display.drawRect(x, y, w, h, _curr_color);
-  if (width() >= height() && w > 2 && h > 2)
+  if (scale() == 2 && w > 2 && h > 2)
     display.drawRect(x + 1, y + 1, w - 2, h - 2, _curr_color);
 }
 
@@ -270,8 +269,9 @@ void GxEPDDisplay::drawXbm(int x, int y, const uint8_t* bits, int w, int h) {
 uint16_t GxEPDDisplay::getTextWidth(const char* str) {
   if (_use_lemon && _text_sz == 1) {
     uint16_t total = 0;
+    const int sc = scale();
     const uint8_t* p = (const uint8_t*)str;
-    while (*p) total += lemonXAdvance(decodeUtf8(p));
+    while (*p) total += lemonXAdvance(decodeUtf8(p), sc);
     return total;
   }
   display.setTextWrap(false);

src/helpers/ui/GxEPDDisplay.h

@@ -58,8 +58,9 @@ class GxEPDDisplay : public DisplayDriver {
   uint8_t _partial_count = 0;
 
   static uint32_t decodeUtf8(const uint8_t*& p);
-  int16_t drawLemonChar(int16_t x, int16_t y, uint32_t cp);
-  uint8_t lemonXAdvance(uint32_t cp);
+  int16_t drawLemonChar(int16_t x, int16_t y, uint32_t cp, int sc);
+  uint8_t lemonXAdvance(uint32_t cp, int sc);
+  int scale() const { return (width() >= height()) ? 2 : 1; }
 
 public:
 #if defined(EINK_DISPLAY_MODEL)
@@ -77,13 +78,13 @@ public:
   // Size 1 scales with orientation (portrait 1×, landscape 2×); size 2 is always 12×16;
   // size 3 is FreeSans18pt (~17×28). Landscape = width >= height.
   int getCharWidth() const override {
-    int sc = (width() >= height()) ? 2 : 1;
+    int sc = scale();
     if (_text_sz == 3) return 17;
     if (_text_sz == 2) return 12 * sc;
     return (_use_lemon ? 5 : 6) * sc;
   }
   int getLineHeight() const override {
-    int sc = (width() >= height()) ? 2 : 1;
+    int sc = scale();
     if (_text_sz == 3) return 28;
     if (_text_sz == 2) return 16 * sc;
     return (_use_lemon ? 10 : 8) * sc;