add VGroup and HGroup convenience widgets

The are convenience Container sublasses which make it easier to create
horizontal and vertical layouts without resort to custom 'constraint'
declarations.

enaml/widgets/api.py

@@ -26,6 +26,7 @@
 from .form import Form
 from .frame import Border
 from .group_box import GroupBox
+from .h_group import HGroup
 from .html import Html
 from .image_view import ImageView
 from .label import Label
@@ -57,6 +58,7 @@
 from .time_selector import TimeSelector
 from .timer import Timer
 from .tool_bar import ToolBar
+from .v_group import VGroup
 from .vtk_canvas import VTKCanvas
 from .web_view import WebView
 from .window import Window

enaml/widgets/h_group.py

@@ -0,0 +1,65 @@
+#------------------------------------------------------------------------------
+# Copyright (c) 2014, Nucleic Development Team.
+#
+# Distributed under the terms of the Modified BSD License.
+#
+# The full license is in the file COPYING.txt, distributed with this software.
+#------------------------------------------------------------------------------
+from atom.api import Bool, Int, Typed, observe
+
+from enaml.core.declarative import d_
+from enaml.layout.layout_helpers import align, hbox
+from enaml.layout.spacers import Spacer
+
+from .container import Container
+
+
+class HGroup(Container):
+    """ A Container subclass which groups child widgets horizontally.
+
+    User constraints are applied *in addition* to the horizontal group
+    constraints. Widgets are aligned along their vertical center.
+
+    """
+    #: The horizontal spacing to place between widgets.
+    spacing = d_(Int(10))
+
+    #: The optional spacer to add as the first layout item.
+    leading_spacer = d_(Typed(Spacer))
+
+    #: The optional spacer to add as the last layout item.
+    trailing_spacer = d_(Typed(Spacer))
+
+    #: Whether to align the widths of the widgets.
+    align_widths = d_(Bool(True))
+
+    #--------------------------------------------------------------------------
+    # Observers
+    #--------------------------------------------------------------------------
+    @observe('spacing', 'leading_spacer', 'trailing_spacer', 'align_widths')
+    def _layout_invalidated(self, change):
+        """ A private observer which invalidates the layout.
+
+        """
+        # The superclass handler is sufficient.
+        super(HGroup, self)._layout_invalidated(change)
+
+    #--------------------------------------------------------------------------
+    # Layout Constraints
+    #--------------------------------------------------------------------------
+    def layout_constraints(self):
+        """ The constraints generation for a HGroup.
+
+        This method supplies horizontal group constraints for the
+        children of the container in addition to any user-supplied
+        constraints.
+
+        """
+        widgets = self.visible_widgets()
+        items = [self.leading_spacer] + widgets + [self.trailing_spacer]
+        cns = self.constraints[:]
+        cns.append(hbox(*items, spacing=self.spacing))
+        cns.append(align('v_center', *widgets))
+        if self.align_widths:
+            cns.append(align('width', *widgets))
+        return cns

enaml/widgets/v_group.py

@@ -0,0 +1,60 @@
+#------------------------------------------------------------------------------
+# Copyright (c) 2014, Nucleic Development Team.
+#
+# Distributed under the terms of the Modified BSD License.
+#
+# The full license is in the file COPYING.txt, distributed with this software.
+#------------------------------------------------------------------------------
+from atom.api import Int, Typed, observe
+
+from enaml.core.declarative import d_
+from enaml.layout.layout_helpers import align, vbox
+from enaml.layout.spacers import Spacer
+
+from .container import Container
+
+
+class VGroup(Container):
+    """ A Container subclass which groups child widgets vertically.
+
+    User constraints are applied *in addition* to the vertical group
+    constraints. Widgets are aligned along their left edge.
+
+    """
+    #: The vertical spacing to place between widgets.
+    spacing = d_(Int(10))
+
+    #: The optional spacer to add as the first layout item.
+    leading_spacer = d_(Typed(Spacer))
+
+    #: The optional spacer to add as the last layout item.
+    trailing_spacer = d_(Typed(Spacer))
+
+    #--------------------------------------------------------------------------
+    # Observers
+    #--------------------------------------------------------------------------
+    @observe('spacing', 'leading_spacer', 'trailing_spacer')
+    def _layout_invalidated(self, change):
+        """ A private observer which invalidates the layout.
+
+        """
+        # The superclass handler is sufficient.
+        super(VGroup, self)._layout_invalidated(change)
+
+    #--------------------------------------------------------------------------
+    # Layout Constraints
+    #--------------------------------------------------------------------------
+    def layout_constraints(self):
+        """ The constraints generation for a VGroup.
+
+        This method supplies left-aligned vertical group constraints for
+        the children of the container in addition to any user-supplied
+        constraints.
+
+        """
+        widgets = self.visible_widgets()
+        items = [self.leading_spacer] + widgets + [self.trailing_spacer]
+        cns = self.constraints[:]
+        cns.append(vbox(*items, spacing=self.spacing))
+        cns.append(align('left', *widgets))
+        return cns