feat(power): dim the backlight after ten idle seconds

src/main.cpp

@@ -43,6 +43,22 @@ static void fallbackScreen(const char* message) {
   halted = true;
 }
 
+// ponytail: fixed 10s / 8% dim, no fade. Make it a setting when someone asks.
+constexpr uint32_t kDimAfterMs = 10000;
+constexpr int kBacklightChannel = 0;
+uint32_t lastTouchMs = 0;
+bool dimmed = false;
+
+void updateBacklight() {
+  if (touch.touched())
+    lastTouchMs = millis();
+  bool idle = millis() - lastTouchMs > kDimAfterMs;
+  if (idle == dimmed)
+    return;
+  dimmed = idle;
+  ledcWrite(kBacklightChannel, dimmed ? 20 : 255);
+}
+
 void setup() {
   Serial.begin(115200);
 
@@ -61,6 +77,12 @@ void setup() {
   touchSpi.begin(14, 12, 13, TOUCH_CS);
   touch.begin(touchSpi);
 
+  // TFT_eSPI leaves TFT_BL a plain output; LEDC takes it over for dimming.
+  ledcSetup(kBacklightChannel, 5000, 8);
+  ledcAttachPin(TFT_BL, kBacklightChannel);
+  ledcWrite(kBacklightChannel, 255);
+  lastTouchMs = millis();
+
   sdSpi.begin(SD_SCK, SD_MISO, SD_MOSI, SD_CS);
   if (!SD.begin(SD_CS, sdSpi)) {
     fallbackScreen("SD card mount failed");
@@ -79,6 +101,7 @@ void loop() {
     delay(100);
     return;
   }
+  updateBacklight();
   net::loop();
   host.loop();
   // The launcher failing to start is the one error no app can recover from.