[pyclutter] examples: Add constraints example

[Emmanuele Bassi <ebassi src gnome org>]

commit 88af0c1d37e5c612fc71ebc43c306c82e57f1f1c
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Apr 13 10:56:50 2015 +0100

    examples: Add constraints example
    
    Ported from C.

 examples/Makefile.am    |    3 +-
 examples/constraints.py |   62 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletions(-)
---
diff --git a/examples/Makefile.am b/examples/Makefile.am
index c07f55d..1d7ac5b 100644
--- a/examples/Makefile.am
+++ b/examples/Makefile.am
@@ -1,2 +1,3 @@
 EXTRA_DIST = \
-       basic-actor.py
+       basic-actor.py \
+       constraints.py
diff --git a/examples/constraints.py b/examples/constraints.py
new file mode 100644
index 0000000..404feb1
--- /dev/null
+++ b/examples/constraints.py
@@ -0,0 +1,62 @@
+from gi.repository import Clutter
+
+if __name__ == '__main__':
+    # The main stage
+    stage = Clutter.Stage(title='Constraints', user_resizable=True)
+    stage.props.background_color = Clutter.Color.get_static(Clutter.StaticColor.ALUMINIUM_1)
+    stage.connect('destroy', Clutter.main_quit)
+
+    # First actor, with a fixed (100, 25) size
+    layer_a = Clutter.Actor()
+    layer_a.props.background_color = Clutter.Color.get_static(Clutter.StaticColor.SCARLET_RED)
+    layer_a.set_size(100, 25)
+    stage.add_child(layer_a)
+
+    # The first actor is anchored to the center of the stage
+    layer_a.add_constraint(Clutter.AlignConstraint(source=stage, align_axis=Clutter.AlignAxis.BOTH, 
factor=0.5))
+
+    # Second actor, with no explicit size
+    layer_b = Clutter.Actor()
+    layer_b.props.background_color = Clutter.Color.get_static(Clutter.StaticColor.BUTTER_DARK)
+    stage.add_child(layer_b)
+
+    # The second actor tracks the X coordinate and the width of the first actor
+    layer_b.add_constraint(Clutter.BindConstraint(source=layer_a, coordinate=Clutter.BindCoordinate.X))
+    layer_b.add_constraint(Clutter.BindConstraint(source=layer_a, coordinate=Clutter.BindCoordinate.WIDTH))
+
+    # The second actor is snapped between the bottom edge of the first actor
+    # and the bottom edge of the stage; vertical spacing of 10px is added for
+    # padding
+    layer_b.add_constraint(Clutter.SnapConstraint(source=layer_a,
+                                                  from_edge=Clutter.SnapEdge.TOP,
+                                                  to_edge=Clutter.SnapEdge.BOTTOM,
+                                                  offset=10))
+    layer_b.add_constraint(Clutter.SnapConstraint(source=stage,
+                                                  from_edge=Clutter.SnapEdge.BOTTOM,
+                                                  to_edge=Clutter.SnapEdge.BOTTOM,
+                                                  offset=-10))
+
+    # The third actor, again with no explicit size
+    layer_c = Clutter.Actor()
+    layer_c.props.background_color = Clutter.Color.get_static(Clutter.StaticColor.CHAMELEON_LIGHT)
+    stage.add_child(layer_c)
+
+    # Like the second actor, the third one also track the X coordinate and
+    # width of the first actor
+    layer_c.add_constraint(Clutter.BindConstraint(source=layer_a, coordinate=Clutter.BindCoordinate.X))
+    layer_c.add_constraint(Clutter.BindConstraint(source=layer_a, coordinate=Clutter.BindCoordinate.WIDTH))
+
+    # The third layer is snapped between the top of the first layer and
+    # the top of the stage
+    layer_c.add_constraint(Clutter.SnapConstraint(source=layer_a,
+                                                  from_edge=Clutter.SnapEdge.BOTTOM,
+                                                  to_edge=Clutter.SnapEdge.TOP,
+                                                  offset=-10))
+    layer_c.add_constraint(Clutter.SnapConstraint(source=stage,
+                                                  from_edge=Clutter.SnapEdge.TOP,
+                                                  to_edge=Clutter.SnapEdge.TOP,
+                                                  offset=10))
+
+    stage.show()
+
+    Clutter.main()