NumericWidget : Mouse wheel adjust value

Fixes GafferHQ#6009.

Changes.md

@@ -19,6 +19,7 @@ Improvements
   - Improved layout of Box node plug creator visibility toggles.
 - ArnoldShader : Moved the `toon` shader's `*_tonemap_hue_saturation` parameters to appropriate sections in the UI.
 - File Browser : The "Type" column can now be sorted. This sorts directories separately from files, which are sorted by their extension.
+- NumericWidget : Added the ability to use the mouse wheel to adjust values in the same manner as <kbd>Up</kbd> and <kbd>Down</kbd> (#6009).
 
 Fixes
 -----

python/GafferUI/NumericWidget.py

@@ -60,6 +60,7 @@ def __init__( self, value, **kw ) :
 		self.__dragStart = None
 
 		self.keyPressSignal().connect( Gaffer.WeakMethod( self.__keyPress ), scoped = False )
+		self.wheelSignal().connect( Gaffer.WeakMethod( self.__wheel ), scoped = False )
 		self.buttonPressSignal().connect( Gaffer.WeakMethod( self.__buttonPress ), scoped = False )
 		self.dragBeginSignal().connect( Gaffer.WeakMethod( self.__dragBegin ), scoped = False )
 		self.dragEnterSignal().connect( Gaffer.WeakMethod( self.__dragEnter ), scoped = False )
@@ -141,6 +142,19 @@ def __keyPress( self, widget, event ) :
 
 		return False
 
+	def __wheel( self, widget, event ) :
+
+		assert( widget is self )
+
+		if not self.getEditable() :
+			return False
+
+		scaleFactor = 15.0
+
+		self.__incrementIndex( self.getCursorPosition(), event.wheelRotation / scaleFactor )
+
+		return True
+
 	def __incrementIndex( self, index, increment ) :
 
 		text = self.getText()