Implement battery low mode rendering and update logic

src/ui/FaceRenderer.cpp

@@ -36,12 +36,18 @@ void FaceRenderer::loop(const MoistureSensor& moisture, const BatterySensor& bat
 
   updateMood(moisture.percent());
   updateDeathMode(now);
+  updateBatteryLowMode(battery.percent());
 
   if (_deadMode) {
     renderDead(now, battery);
     return;
   }
 
+  if (_batteryLowMode) {
+    renderBatteryLow(now, battery);
+    return;
+  }
+
   if (_mood == HAPPY) updateHappy(now);
   else if (_mood == DRY) updateDry(now);
   else updateTooWet(now);
@@ -76,6 +82,11 @@ void FaceRenderer::updateDeathMode(unsigned long now) {
   }
 }
 
+void FaceRenderer::updateBatteryLowMode(int batteryPercent) {
+  // Enter nervous mode when battery is critically low (< 10%)
+  _batteryLowMode = (batteryPercent < 10);
+}
+
 void FaceRenderer::updateHappy(unsigned long now) {
   if ((long)(now - _nextGazeMs) >= 0) {
     _targetX = randRangeI8(-3, 3);
@@ -151,6 +162,48 @@ void FaceRenderer::renderDead(unsigned long now, const BatterySensor& battery) {
   d.display();
 }
 
+void FaceRenderer::renderBatteryLow(unsigned long now, const BatterySensor& battery) {
+  auto &d = _display->oled();
+  d.clearDisplay();
+
+  // Nervous animation: eyes glance up at battery icon repeatedly
+  // Battery icon is at (110, 2) in top-right corner
+  // Eyes are centered at (40, 24) for left, (88, 24) for right
+
+  // Create a glancing pattern: look up at battery, then center, repeat
+  int glancePhase = (now / 800) % 3;  // 3 phases: up, center, up
+
+  int pupilX = 0, pupilY = 0;
+
+  if (glancePhase == 0 || glancePhase == 2) {
+    // Look up toward battery icon (upper right)
+    pupilX = 3;   // Look right
+    pupilY = -4;  // Look up
+  } else {
+    // Brief center position between glances
+    pupilX = 0;
+    pupilY = -2;  // Still slightly upward (worried/anxious)
+  }
+
+  // Draw eyes with pupils positioned
+  if (_blinking) {
+    drawEyesClosed();
+  } else {
+    drawEyesOpen(pupilX, pupilY);
+  }
+
+  // Worried eyebrows
+  drawBrowsWorried();
+
+  // Nervous mouth (wavy/uncertain)
+  drawMouthNervous();
+
+  // Draw battery icon in top-right corner (blinking)
+  _display->drawBatteryIcon(110, 2, battery.percent(), true);
+
+  d.display();
+}
+
 void FaceRenderer::renderNormal(unsigned long now, const BatterySensor& battery) {
   auto &d = _display->oled();
   d.clearDisplay();
@@ -212,6 +265,15 @@ void FaceRenderer::drawBrowsVerySad() {
   d.drawLine(80, 18, 102, 12, 1);
 }
 
+void FaceRenderer::drawBrowsWorried() {
+  auto &d = _display->oled();
+  // Raised/arched worried eyebrows
+  d.drawLine(26, 14, 36, 10, 1);
+  d.drawLine(36, 10, 48, 12, 1);
+  d.drawLine(80, 12, 92, 10, 1);
+  d.drawLine(92, 10, 102, 14, 1);
+}
+
 void FaceRenderer::drawMouthHappy() {
   auto &d = _display->oled();
   for (int i = 0; i < 5; i++)
@@ -229,6 +291,15 @@ void FaceRenderer::drawMouthFlat() {
   d.drawLine(52, 48, 76, 48, 1);
 }
 
+void FaceRenderer::drawMouthNervous() {
+  auto &d = _display->oled();
+  // Wavy/uncertain nervous mouth
+  d.drawLine(52, 48, 58, 47, 1);
+  d.drawLine(58, 47, 64, 48, 1);
+  d.drawLine(64, 48, 70, 47, 1);
+  d.drawLine(70, 47, 76, 48, 1);
+}
+
 void FaceRenderer::drawBubbles(int off) {
   auto &d = _display->oled();
   d.drawCircle(10 + off, 12, 4, 1);