Ensure opacity is applied to DrawNode used in Label (#2396)

* Ensure opacity is applied to label underline

* Set DrawNode opacity

* Apply formatting

Author: rh101

core/2d/Label.cpp

@@ -1503,7 +1503,9 @@ void Label::enableUnderline()
     {
         _lineDrawNode = DrawNode::create();
         _lineDrawNode->setGlobalZOrder(getGlobalZOrder());
-        _lineDrawNode->properties.setFactor(_lineDrawNode->properties.getFactor() * 2.0f);  // 2.0f: Makes the line smaller 
+        _lineDrawNode->setOpacity(_displayedOpacity);
+        _lineDrawNode->properties.setFactor(_lineDrawNode->properties.getFactor() *
+                                            2.0f);  // 2.0f: Makes the line smaller 
         addChild(_lineDrawNode, 100000);
     }
 }
@@ -1520,7 +1522,9 @@ void Label::enableStrikethrough()
     {
         _lineDrawNode = DrawNode::create();
         _lineDrawNode->setGlobalZOrder(getGlobalZOrder());
-        _lineDrawNode->properties.setFactor(_lineDrawNode->properties.getFactor() * 2.0f); // 2.0f: Makes the line smaller 
+        _lineDrawNode->setOpacity(_displayedOpacity);
+        _lineDrawNode->properties.setFactor(_lineDrawNode->properties.getFactor() *
+                                            2.0f);  // 2.0f: Makes the line smaller 
         addChild(_lineDrawNode, 100000); 
     }
 }
@@ -2424,6 +2428,12 @@ void Label::updateDisplayedOpacity(uint8_t parentOpacity)
     {
         it.second->updateDisplayedOpacity(_displayedOpacity);
     }
+
+    if (_lineDrawNode)
+    {
+        _lineDrawNode->setOpacity(_displayedOpacity);
+        _contentDirty = true;
+    }
 }
 
 // FIXME: it is not clear what is the difference between setTextColor() and setColor()