ListContainer alignment

Changes.md

@@ -14,6 +14,7 @@ Improvements
 - LightEditor, RenderPassEditor : History windows now use a context determined relative to the current focus node.
 - NumericWidget : Added the ability to use <kbd>Ctrl</kbd> + scroll wheel to adjust values in the same manner as <kbd>Up</kbd> and <kbd>Down</kbd> (#6009). [^1]
 - NodeEditor : Improved performance when showing a node with many colour plugs. Showing the Arnold `standard_surface` shader is now almost 2x faster. [^1]
+- ListContainer : Adding a child widget with non-default alignment no longer causes the container to take up all available space.
 
 Fixes
 -----

python/GafferUI/GraphEditor.py

@@ -74,12 +74,7 @@ def __init__( self, scriptNode, **kw ) :
 		self.__gadgetWidget.getViewportGadget().preRenderSignal().connect( Gaffer.WeakMethod( self.__preRender ) )
 
 		with GafferUI.ListContainer( borderWidth = 8, spacing = 0 ) as overlay :
-			with GafferUI.ListContainer(
-				GafferUI.ListContainer.Orientation.Horizontal,
-				parenting = {
-					"verticalAlignment" : GafferUI.VerticalAlignment.Top,
-				}
-			) :
+			with GafferUI.ListContainer( GafferUI.ListContainer.Orientation.Horizontal ) :
 				GafferUI.Spacer( imath.V2i( 1 ) )
 				GafferUI.MenuButton(
 					image = "annotations.png", hasFrame = False,
@@ -88,6 +83,7 @@ def __init__( self, scriptNode, **kw ) :
 						title = "Annotations"
 					)
 				)
+			GafferUI.Spacer( imath.V2i( 1 ) )
 
 		self.__gadgetWidget.addOverlay( overlay )
 

python/GafferUI/ListContainer.py

@@ -45,6 +45,28 @@
 from Qt import QtWidgets
 from Qt import QtCore
 
+class _WidgetItem( QtWidgets.QWidgetItem ) :
+	# A customized `QWidgetItem` to return a `maximumSize()` without taking
+	# into account its `alignment`. Qt's `QBoxLayout` returns `QLAYOUTSIZE_MAX`
+	# whenever there's an alignment set, resulting in unnecessarily greedy
+	# aligned layouts. We override `QWidgetItem` instead of `QBoxLayout`
+	# because in `QBoxLayout.insertWidget()`, the widget is wrapped in a
+	# `QWidgetItem` object that does its own calculation of `maximumSize()`
+	# rather than defer to the contained widget or its layout.
+
+	def __init__( self, widget ) :
+
+		QtWidgets.QWidgetItem.__init__( self, widget )
+
+	def maximumSize( self ) :
+
+		a = self.alignment()
+		self.setAlignment( QtCore.Qt.Alignment() )
+		s = QtWidgets.QWidgetItem.maximumSize( self )
+		self.setAlignment( a )
+
+		return s
+
 ## The ListContainer holds a series of Widgets either in a column or a row.
 # It attempts to provide a list like interface for manipulation of the widgets.
 class ListContainer( GafferUI.ContainerWidget ) :
@@ -86,7 +108,12 @@ def append( self, child, expand=False, horizontalAlignment=None, verticalAlignme
 		self.__widgets.append( child )
 
 		stretch = 1 if expand else 0
-		self.__qtLayout.addWidget( child._qtWidget(), stretch, self.__convertToQtAlignment( horizontalAlignment, verticalAlignment ) )
+
+		if horizontalAlignment is not None or verticalAlignment is not None :
+			self.__qtLayout.addItem( self.__widgetItem( child._qtWidget(), horizontalAlignment, verticalAlignment ) )
+		else :
+			self.__qtLayout.addWidget( child._qtWidget(), stretch, self.__convertToQtAlignment( horizontalAlignment, verticalAlignment ) )
+
 		child._applyVisibility()
 
 	def remove( self, child ) :
@@ -106,7 +133,11 @@ def insert( self, index, child, expand=False, horizontalAlignment=None, vertical
 		self.__widgets.insert( index, child )
 
 		stretch = 1 if expand else 0
-		self.__qtLayout.insertWidget( index, child._qtWidget(), stretch, self.__convertToQtAlignment( horizontalAlignment, verticalAlignment ) )
+
+		if horizontalAlignment is not None or verticalAlignment is not None :
+			self.__qtLayout.insertItem( index, self.__widgetItem( child._qtWidget(), horizontalAlignment, verticalAlignment ) )
+		else :
+			self.__qtLayout.insertWidget( index, child._qtWidget(), stretch, self.__convertToQtAlignment( horizontalAlignment, verticalAlignment ) )
 		child._applyVisibility()
 
 	def index( self, child ) :
@@ -178,6 +209,16 @@ def __len__( self ) :
 
 		return len( self.__widgets )
 
+	def __widgetItem( self, qtWidget, horizontalAlignment, verticalAlignment ) :
+
+		# Duplicate the logic in `QBoxLayout.insertWidget()` but with our
+		# customized `QWidgetItem`.
+		self._qtWidget().layout().addChildWidget( qtWidget )
+		widgetItem = _WidgetItem( qtWidget )
+		widgetItem.setAlignment( self.__convertToQtAlignment( horizontalAlignment, verticalAlignment ) )
+
+		return widgetItem
+
 	def __convertToQtAlignment( self, horizontalAlignment, verticalAlignment):
 
 		if not horizontalAlignment and not verticalAlignment:

python/GafferUITest/ListContainerTest.py

@@ -370,5 +370,19 @@ def testSliceSetItemAtEnd( self ) :
 		self.assertEqual( c[0].s, "a" )
 		self.assertEqual( c[1].s, "b" )
 
+	def testAlignmentSize( self ) :
+
+		with GafferUI.Window( "Test" ) as w :
+			with GafferUI.ListContainer( GafferUI.ListContainer.Orientation.Vertical ) as v :
+				l1 = GafferUI.Label( "test", parenting = { "verticalAlignment" : GafferUI.VerticalAlignment.Top } )
+				l2 = GafferUI.Label( "test" )
+
+		w._qtWidget().resize( 200, 200 )
+		w.setVisible( True )
+		self.waitForIdle()
+
+		self.assertEqual( v.size().y, l1.size().y + l2.size().y )
+		self.assertEqual( l2._qtWidget().pos().y(), l1.size().y )
+
 if __name__ == "__main__":
 	unittest.main()