LCD_BACKLIGHT_TIMEOUT support for neopixel LCDs.

Marlin/Configuration.h

@@ -3403,7 +3403,8 @@
   // Use some of the NeoPixel LEDs for static (background) lighting
   //#define NEOPIXEL_BKGD_INDEX_FIRST   0 // Index of the first background LED
   //#define NEOPIXEL_BKGD_INDEX_LAST    5 // Index of the last background LED
-  //#define NEOPIXEL_BKGD_COLOR { 255, 255, 255, 0 }  // R, G, B, W
+  //#define NEOPIXEL_BKGD_COLOR         { 255, 255, 255, 0 }  // R, G, B, W
+  //#define NEOPIXEL_BKGD_TIMEOUT_COLOR {  25,  25,  25, 0 }  // R, G, B, W
   //#define NEOPIXEL_BKGD_ALWAYS_ON       // Keep the backlight on when other NeoPixels are off
 #endif
 

Marlin/src/feature/leds/neopixel.cpp

@@ -54,7 +54,15 @@ Adafruit_NeoPixel Marlin_NeoPixel::adaneo1(NEOPIXEL_PIXELS, NEOPIXEL_PIN, NEOPIX
     set_background_color(background_color);
   }
 
-#endif
+  void Marlin_NeoPixel::set_background_off() {
+    #ifndef NEOPIXEL_BKGD_TIMEOUT_COLOR
+      #define NEOPIXEL_BKGD_TIMEOUT_COLOR { 0, 0, 0, 0 }
+    #endif
+    constexpr uint8_t background_color_off[4] = NEOPIXEL_BKGD_TIMEOUT_COLOR;
+    set_background_color(background_color_off);
+  }
+
+#endif // NEOPIXEL_BKGD_INDEX_FIRST
 
 void Marlin_NeoPixel::set_color(const uint32_t color) {
   if (neoindex >= 0) {

Marlin/src/feature/leds/neopixel.h

@@ -91,6 +91,7 @@ class Marlin_NeoPixel {
     static void set_background_color(const uint8_t r, const uint8_t g, const uint8_t b, const uint8_t w);
     static void set_background_color(const uint8_t (&rgbw)[4]) { set_background_color(rgbw[0], rgbw[1], rgbw[2], rgbw[3]); }
     static void reset_background_color();
+    static void set_background_off();
   #endif
 
   static void begin() {

Marlin/src/inc/SanityCheck.h

@@ -3241,8 +3241,14 @@ static_assert(X_MAX_LENGTH >= X_BED_SIZE, "Movement bounds (X_MIN_POS, X_MAX_POS
 #if LCD_BACKLIGHT_TIMEOUT_MINS
   #if !HAS_ENCODER_ACTION
     #error "LCD_BACKLIGHT_TIMEOUT_MINS requires an LCD with encoder or keypad."
+  #elif ENABLED(NEOPIXEL_BKGD_INDEX_FIRST)
+    #if PIN_EXISTS(LCD_BACKLIGHT)
+      #error "LCD_BACKLIGHT_PIN and NEOPIXEL_BKGD_INDEX_FIRST are not supported at the same time."
+    #elif ENABLED(NEOPIXEL_BKGD_ALWAYS_ON)
+      #error "LCD_BACKLIGHT_TIMEOUT is not compatible with NEOPIXEL_BKGD_ALWAYS_ON."
+    #endif
   #elif !PIN_EXISTS(LCD_BACKLIGHT)
-    #error "LCD_BACKLIGHT_TIMEOUT_MINS requires LCD_BACKLIGHT_PIN."
+    #error "LCD_BACKLIGHT_TIMEOUT_MINS requires either LCD_BACKLIGHT_PIN or NEOPIXEL_BKGD_INDEX_FIRST."
   #endif
 #endif
 

Marlin/src/lcd/marlinui.cpp

@@ -24,7 +24,7 @@
 
 #include "../MarlinCore.h" // for printingIsPaused
 
-#if LED_POWEROFF_TIMEOUT > 0 || BOTH(HAS_WIRED_LCD, PRINTER_EVENT_LEDS)
+#if LED_POWEROFF_TIMEOUT > 0 || BOTH(HAS_WIRED_LCD, PRINTER_EVENT_LEDS) || (defined(LCD_BACKLIGHT_TIMEOUT_MINS) && defined(NEOPIXEL_BKGD_INDEX_FIRST))
   #include "../feature/leds/leds.h"
 #endif
 
@@ -186,12 +186,17 @@ constexpr uint8_t epps = ENCODER_PULSES_PER_STEP;
 #if LCD_BACKLIGHT_TIMEOUT_MINS
 
   constexpr uint8_t MarlinUI::backlight_timeout_min, MarlinUI::backlight_timeout_max;
-
   uint8_t MarlinUI::backlight_timeout_minutes; // Initialized by settings.load()
   millis_t MarlinUI::backlight_off_ms = 0;
+
   void MarlinUI::refresh_backlight_timeout() {
     backlight_off_ms = backlight_timeout_minutes ? millis() + backlight_timeout_minutes * 60UL * 1000UL : 0;
-    WRITE(LCD_BACKLIGHT_PIN, HIGH);
+    #ifdef NEOPIXEL_BKGD_INDEX_FIRST
+      neo.reset_background_color();
+      neo.show();
+    #elif PIN_EXISTS(LCD_BACKLIGHT)
+      WRITE(LCD_BACKLIGHT_PIN, HIGH);
+    #endif
   }
 
 #elif HAS_DISPLAY_SLEEP
@@ -1196,8 +1201,14 @@ void MarlinUI::init() {
       #endif
 
       #if LCD_BACKLIGHT_TIMEOUT_MINS
+
         if (backlight_off_ms && ELAPSED(ms, backlight_off_ms)) {
-          WRITE(LCD_BACKLIGHT_PIN, LOW); // Backlight off
+          #ifdef NEOPIXEL_BKGD_INDEX_FIRST
+            neo.set_background_off();
+            neo.show();
+          #elif PIN_EXIST(LCD_BACKLIGHT)
+            WRITE(LCD_BACKLIGHT_PIN, LOW); // Backlight off
+          #endif
           backlight_off_ms = 0;
         }
       #elif HAS_DISPLAY_SLEEP

buildroot/tests/LPC1768

@@ -17,7 +17,7 @@ restore_configs
 opt_set MOTHERBOARD BOARD_RAMPS_14_RE_ARM_EFB SERIAL_PORT_3 3 \
         NEOPIXEL_TYPE NEO_RGB RGB_LED_R_PIN P2_12 RGB_LED_G_PIN P1_23 RGB_LED_B_PIN P1_22 RGB_LED_W_PIN P1_24
 opt_enable FYSETC_MINI_12864_2_1 SDSUPPORT SDCARD_READONLY SERIAL_PORT_2 RGBW_LED E_DUAL_STEPPER_DRIVERS \
-           NEOPIXEL_LED NEOPIXEL_IS_SEQUENTIAL NEOPIXEL_STARTUP_TEST NEOPIXEL_BKGD_INDEX_FIRST NEOPIXEL_BKGD_INDEX_LAST NEOPIXEL_BKGD_COLOR NEOPIXEL_BKGD_ALWAYS_ON
+           NEOPIXEL_LED NEOPIXEL_IS_SEQUENTIAL NEOPIXEL_STARTUP_TEST NEOPIXEL_BKGD_INDEX_FIRST NEOPIXEL_BKGD_INDEX_LAST NEOPIXEL_BKGD_COLOR NEOPIXEL_BKGD_TIMEOUT_COLOR NEOPIXEL_BKGD_ALWAYS_ON
 exec_test $1 $2 "ReARM EFB VIKI2, SDSUPPORT, 2 Serial ports (USB CDC + UART0), NeoPixel" "$3"
 
 #restore_configs