Add utility function to expose if strip is being updated

wled00/FX.h

@@ -480,7 +480,9 @@ class WS2812FX {
       gammaCorrectCol = true,
       applyToAllSelected = true,
       segmentsAreIdentical(Segment* a, Segment* b),
-      setEffectConfig(uint8_t m, uint8_t s, uint8_t i, uint8_t p);
+      setEffectConfig(uint8_t m, uint8_t s, uint8_t i, uint8_t p),
+      // return true if the strip is being sent pixel updates
+      isUpdating(void);
 
     uint8_t
       mainSegment = 0,

wled00/FX_fcn.cpp

@@ -218,8 +218,11 @@ void WS2812FX::setPixelColor(uint16_t i, byte r, byte g, byte b, byte w)
                               //you can set it to 0 if the ESP is powered by USB and the LEDs by external
 
 void WS2812FX::show(void) {
-  if (_callback) _callback();
-  
+
+  // avoid race condition, caputre _callback value
+  show_callback callback = _callback;
+  if (callback) callback();
+
   //power limit calculation
   //each LED can draw up 195075 "power units" (approx. 53mA)
   //one PU is the power it takes to have 1 channel 1 step brighter per brightness step
@@ -291,10 +294,24 @@ void WS2812FX::show(void) {
     bus->SetBrightness(_brightness);
   }
   
+  // some buses send asynchronously and this method will return before
+  // all of the data has been sent.
+  // See https://github.com/Makuna/NeoPixelBus/wiki/ESP32-NeoMethods#neoesp32rmt-methods
   bus->Show();
   _lastShow = millis();
 }
 
+/**
+ * Returns a true value if any of the strips are still being updated.
+ * On some hardware (ESP32), strip updates are done asynchronously.
+ */
+bool WS2812FX::isUpdating() {
+  return !bus->CanShow();
+}
+
+/**
+ * Forces the next frame to be computed on all active segments.
+ */
 void WS2812FX::trigger() {
   _triggered = true;
 }

wled00/NpbWrapper.h

@@ -296,7 +296,6 @@ public:
 
   void Show()
   {
-    byte b;
     switch (_type)
     {
       case NeoPixelType_Grb:  _pGrb->Show();  break;
@@ -304,6 +303,22 @@ public:
     }
   }
 
+  /** 
+   * This will return true if enough time has passed since the last time Show() was called. 
+   * This also means that calling Show() will not cause any undue waiting. If the method for 
+   * the defined bus is hardware that sends asynchronously, then call CanShow() will let 
+   * you know if it has finished sending the data from the last Show().
+   */
+  bool CanShow()
+  {
+    switch (_type)
+    {
+      case NeoPixelType_Grb:  return _pGrb->CanShow();
+      case NeoPixelType_Grbw: return _pGrbw->CanShow();
+      default: return true;
+    }
+  }
+
   void SetPixelColor(uint16_t indexPixel, RgbwColor c)
   {
     RgbwColor col;