# Multiple engines example

An example to show how you can have multiple engines in one application.

Mutliple engines can be useful for more separation, eg to script each engine separately, or to avoid side effects between scenes.

This example shows how to explicitly set the engine for an embedded scene.

To define default arguments, it makes use of the Traits initialization style, rather than overriding the __init__.

Python source code: `multiple_engines.py`

    # Author:  Gael Varoquaux <gael _dot_ varoquaux _at_ normalesup _dot_ org>
    # Copyright (c) 2009, Enthought, Inc.
    # License: BSD Style.

    from traits.api import HasTraits, Instance, on_trait_change
    from traitsui.api import View, Group, Item

    from mayavi.core.api import Engine
    from mayavi.core.ui.api import MayaviScene, MlabSceneModel, \
                SceneEditor

    ################################################################################
    class MyApp(HasTraits):

        # The first engine. As default arguments (an empty tuple) are given,
        # traits initializes it.
        engine1 = Instance(Engine, args=())

        scene1 = Instance(MlabSceneModel)

        def _scene1_default(self):
            " The default initializer for 'scene1' "
            self.engine1.start()
            scene1 = MlabSceneModel(engine=self.engine1)
            return scene1

        engine2 = Instance(Engine, ())

        scene2 = Instance(MlabSceneModel)

        def _scene2_default(self):
            " The default initializer for 'scene2' "
            self.engine2.start()
            scene2 = MlabSceneModel(engine=self.engine2)
            return scene2

        # We populate the scenes only when it is activated, to avoid problems
        # with VTK objects that expect an active scene
        @on_trait_change('scene1.activated')
        def populate_scene1(self):
            self.scene1.mlab.test_surf()

        @on_trait_change('scene2.activated')
        def populate_scene2(self):
            self.scene2.mlab.test_mesh()

        # The layout of the view
        view = View(Group(Item('scene1',
                            editor=SceneEditor(scene_class=MayaviScene),
                            width=480, height=480)),
                    Group(Item('scene2',
                            editor=SceneEditor(scene_class=MayaviScene),
                            width=480, height=480)),
                    resizable=True)

    if __name__ == '__main__':
        MyApp().configure_traits()