Slider : Fix extra entries in undo queue on drag

Changes.md

@@ -6,6 +6,7 @@ Fixes
 
 - ImageReader : Fixed crash caused by invalid OpenEXR `multiView` attributes.
 - LightEditor, RenderPassEditor : Added missing icon representing use of the `CreateIfMissing` tweak mode in the history window.
+- Slider : Fixed bug where two undo steps were needed to get back to the original value when dragging.
 
 1.3.16.6 (relative to 1.3.16.5)
 ========

python/GafferUI/Slider.py

@@ -429,6 +429,11 @@ def __buttonPress( self, widget, event ) :
 	def __dragBegin( self, widget, event ) :
 
 		if event.buttons == GafferUI.ButtonEvent.Buttons.Left and self.getSelectedIndex() is not None :
+			self.__setValueInternal(
+				self.getSelectedIndex(),
+				self.__eventValue( event ),
+				self.ValueChangedReason.DragBegin
+			)
 			return IECore.NullObject.defaultNullObject()
 
 		return None
@@ -450,7 +455,11 @@ def __dragMove( self, widget, event ) :
 
 	def __dragEnd( self, widget, event ) :
 
-		self.__dragMove( widget, event )
+		self.__setValueInternal(
+			self.getSelectedIndex(),
+			self.__eventValue( event ),
+			self.ValueChangedReason.DragEnd
+		)
 
 	def __keyPress( self, widget, event ) :