Improve new backlight (#8018)

Backlight function improvement

radio/src/functions.cpp

@@ -356,6 +356,12 @@ void evalFunctions(const CustomFunctionData * functions, CustomFunctionsContext
 
           case FUNC_BACKLIGHT:
           {
+            newActiveFunctions |= (1u << FUNCTION_BACKLIGHT);
+            if (!CFN_PARAM(cfn)) {  // When no source is set, backlight works like original backlight and turn on regardless of backlight settings
+              requiredBacklightBright = BACKLIGHT_FORCED_ON;
+              break;
+            }
+
             getvalue_t raw = getValue(CFN_PARAM(cfn));
 #if defined(COLORLCD)
             if (raw == -1024)

radio/src/opentx.cpp

@@ -695,20 +695,27 @@ void checkBacklight()
       }
     }
 
-    bool backlightOn = (g_eeGeneral.backlightMode == e_backlight_mode_on || (g_eeGeneral.backlightMode != e_backlight_mode_off && lightOffCounter));
-
-    if (flashCounter) {
-      backlightOn = !backlightOn;
-    }
-
-    if (backlightOn) {
-      currentBacklightBright = requiredBacklightBright;
+    if (requiredBacklightBright == BACKLIGHT_FORCED_ON) {
+      currentBacklightBright = g_eeGeneral.backlightBright;
       BACKLIGHT_ENABLE();
     }
     else {
-      BACKLIGHT_DISABLE();
+      bool backlightOn = ((g_eeGeneral.backlightMode == e_backlight_mode_on) ||
+                          (g_eeGeneral.backlightMode != e_backlight_mode_off && lightOffCounter) ||
+                          (g_eeGeneral.backlightMode == e_backlight_mode_off && isFunctionActive(FUNCTION_BACKLIGHT)));
+
+      if (flashCounter) {
+        backlightOn = !backlightOn;
+      }
+
+      if (backlightOn) {
+        currentBacklightBright = requiredBacklightBright;
+        BACKLIGHT_ENABLE();
+      }
+      else {
+        BACKLIGHT_DISABLE();
+      }
     }
-  }
 }
 
 void resetBacklightTimeout()

radio/src/opentx.h

@@ -852,6 +852,7 @@ enum FunctionsActive {
 #endif
   FUNCTION_BACKGND_MUSIC,
   FUNCTION_BACKGND_MUSIC_PAUSE,
+  FUNCTION_BACKLIGHT,
 };
 
 #define VARIO_FREQUENCY_ZERO   700/*Hz*/

radio/src/targets/horus/board.h

@@ -546,7 +546,8 @@ void backlightInit();
 #else
 void backlightEnable(uint8_t dutyCycle = 0);
 #endif
-#define BACKLIGHT_LEVEL_MAX   100
+#define BACKLIGHT_LEVEL_MAX     100
+#define BACKLIGHT_FORCED_ON     BACKLIGHT_LEVEL_MAX + 1
 #if defined(PCBX12S)
 #define BACKLIGHT_LEVEL_MIN   5
 #elif defined(RADIO_FAMILY_T16)

radio/src/targets/sky9x/board.h

@@ -274,6 +274,7 @@ extern "C" {
 #define isBacklightEnabled()           (PWM->PWM_CH_NUM[0].PWM_CDTY != 100)
 #define BACKLIGHT_ENABLE()             backlightEnable()
 #define BACKLIGHT_DISABLE()            backlightDisable()
+#define BACKLIGHT_FORCED_ON            101
 
 // ADC driver
 #define NUM_POTS                       3

radio/src/targets/taranis/board.h

@@ -660,6 +660,7 @@ void pwrResetHandler();
 void backlightInit();
 void backlightDisable();
 #define BACKLIGHT_DISABLE()             backlightDisable()
+#define BACKLIGHT_FORCED_ON             101
 uint8_t isBacklightEnabled();
 #if !defined(__cplusplus)
   #define backlightEnable(...)