
.. _builing_applications:

Building applications using Mayavi
===================================

.. topic:: Section summary

    This section describes how Mayavi can be used as a scientific data
    visualization and 3D plotting tool in interactive application.

Mayavi can be used as a fully integrated and interactive 3D plotting tool
in a GUI application. Using the event model behind Traits and TVTK, all
the different properties of a visualization can be changed dynamically,
including the data visualized itself.

In this section, we first show how an interactive dialog embedding a
Mayavi scene can be built, using `Traits`. Then we show how to integrate
this dialog in a WxPython or a PyQt (or PySide) application.

Custom interactive dialogs
--------------------------

Mayavi and TVTK are entirely built using the Traits library which provides
easy callbacks and visualization for objects attribute. All the different
properties of the pipeline and pipeline objects are expressed as Traits,
i.e. special attributes that can be visualized in dialogs and that fire
callbacks when they are modified. In particular this means that when a
visualization object is modified, the scene can update automatically.

We strongly suggest that you refer to the `Traits`
`documentation <http://docs.enthought.com/traits>`_
for more details.  There are also a list of introductory
`materials <https://support.enthought.com/hc/en-us/articles/204469620-Introductory-materials-for-Traits-and-Traits-UI>`
for learning Traits and Traits UI.

.. _embedding_mayavi_traits:

Embedding a Mayavi scene in a Traits dialog
............................................

To build a custom dialog with a Mayavi scene, the best option is to
create a class deriving from the base `Traits` class. A special
attribute, called SceneModel can be used as an attribute to represent a
Mayavi scene that can accept objects. This defines the `model`, i.e. the
main `HasTraits` object in which the application logics is contained.

A view of this object, as a dialog, can be created using the
`.configure_traits` method of this object. If a view is explicitely
specified the embedded Mayavi scene can be represented with the usual
widget for scene by specifying for it the `SceneEditor`::

    from traits.api import HasTraits, Instance
    from traitsui.api import View, Item
    from tvtk.pyface.scene_model import SceneModel
    from tvtk.pyface.scene_editor import SceneEditor

    class MyModel(HasTraits):
        scene = Instance(SceneModel, ())

        view = View(Item('scene', height=400, show_label=False,
                        editor=SceneEditor()))

    MyModel().configure_traits()

A `Mayavi` button to pop up the pipeline dialog can be added on the
toolbar by specifying a different scene view to the `SceneEditor`::

    from mayavi.core.ui.mayavi_scene import MayaviScene

    #...
    editor=SceneEditor(scene_class=MayaviScene)
    #...

If, on the contrary, you want a view with no toolbar, you can replace the
`MayaviView` by a raw tvtk view::

    from tvtk.pyface.api import Scene

    #...
    editor=SceneEditor(scene_class=Scene)
    #...

The :ref:`example_mayavi_traits_ui` is a fairly comprehensive example that
demonstrates how you can embed almost the entire Mayavi UI into your traits
based UI.

A scene, with `mlab` embedded
..............................

An object representing a scene is interesting only if you can visualize
data with the scene. For this we can instanciate an `Engine` and assign
it to the scene. Having an `Engine` only for one scene allows us to
confine action and visualization objects only to this scene.

We can also use an `MlabSceneModel` instance, rather than a `SceneModel`,
imported from `mayavi.tools.mlab_scene_model`. This scene model
registers the figure in `mlab` (:ref:`simple-scripting-with-mlab`). It
has an embedded mlab attribute, that exposes the mlab commands (see
:ref:`mlab_plotting_functions`). For instance plotting 3D points can be
achieved with `self.scene.mlab.points3d(x, y, z, s)`.

.. warning:: Embedding several scenes in an application

    When using several 'MlabSceneModel' in an application, there is an
    ambiguity regarding which scene mlab should use to plot to. This is
    why relying on using the current figure, as mlab most often does, is
    dangerous.

    The solution to this, is explicitly pass in the Mayavi figure to
    mlab's figure keyword argument::

	mlab.points3d(x, y, z, s, figure=self.scene.mayavi_scene)

    However, this functionality is new in Mayavi 3.2.1.

    A full example with two embedded scenes is given on
    :ref:`example_multiple_mlab_scene_models`.

    Another way of creating isolation between scene is to explicitly
    insert them in different engines. This is demonstrated in
    :ref:`example_multiple_engines`

Making the visualization live
..............................

Having an interactive application is interesting only if you can do
custom, domain-specific, interaction with the visualization.

An important use case is modifying the data visualized as a parameter is
changed interactively. For this we can use the inplace modification of
the data of an mlab object, as for animation of an mlab plot (see
:ref:`mlab-animating-data`). Suppose we are plotting a line curve defined
by a function of two parameters::

    from numpy import linspace, pi, cos, sin

    def curve(n_mer, n_long):
        phi = linspace(0, 2*pi, 2000)
        return [ cos(phi*n_mer) * (1 + 0.5*cos(n_long*phi)),
                sin(phi*n_mer) * (1 + 0.5*cos(n_long*phi)),
                0.5*sin(n_long*phi),
                sin(phi*n_mer)]

Using `mlab`, we could plot the curve with `plot3d`::

    x, y, z, s = curve(4, 6)
    from mayavi import mlab
    plot = mlab.plot3d(x, y, z, s)

Modifying the plot for new parameters could be written::

    x, y, z, t = curve(4, 8)
    plot.mlab_source.trait_set(x=x, y=y, z=z, scalars=t)

In a dialog, this would be::

    from traits.api import HasTraits, Range, Instance, \
                        on_trait_change
    from traitsui.api import View, Item, HGroup
    from tvtk.pyface.scene_editor import SceneEditor
    from mayavi.tools.mlab_scene_model import \
                        MlabSceneModel
    from mayavi.core.ui.mayavi_scene import MayaviScene


    class Visualization(HasTraits):
        meridional = Range(1, 30,  6)
        transverse = Range(0, 30, 11)
        scene      = Instance(MlabSceneModel, ())

        def __init__(self):
            # Do not forget to call the parent's __init__
            HasTraits.__init__(self)
            x, y, z, t = curve(self.meridional, self.transverse)
            self.plot = self.scene.mlab.plot3d(x, y, z, t, colormap='Spectral')

        @on_trait_change('meridional,transverse')
        def update_plot(self):
            x, y, z, t = curve(self.meridional, self.transverse)
            self.plot.mlab_source.trait_set(x=x, y=y, z=z, scalars=t)


        # the layout of the dialog created
        view = View(Item('scene', editor=SceneEditor(scene_class=MayaviScene),
                        height=250, width=300, show_label=False),
                    HGroup(
                            '_', 'meridional', 'transverse',
                        ),
                    )

    visualization = Visualization()
    visualization.configure_traits()

This code creates the following dialog:

.. image:: images/example_mlab_interactive_dialog.jpg
    :align: center

A complete, runnable, code based on the above comments is given in the
:ref:`example_mlab_interactive_dialog`.

.. warning:: Visualization objects and properties created before a scene is available

    When creating a traited object with an embedded scene, the scene can
    be created and populated before a view on it is actually open.
    However, some VTK objects or properties require a scene with a camera
    and interaction to be open to work properly, mainly because either
    they orient themselves to the camera, or deal with interaction with
    keyboard or mouse (such as interactors, eg an implicit plane). As a
    result some property changes on VTK objects will raise warnings or
    simply not work when applied without a dialog opened. When embedding
    a scene in a Traits object, the best option is to create and modify
    these objects only when the scene is activated, by listening to
    changes on the 'scene.activated' traits::

        @on_trait_change('scene.activated')
        def create_plot(self):
            # Do the plotting here
            # ...

    The :ref:`example_lorenz_ui` shows a good example of this situation.

.. topic:: Learning by examples

 Several full-featured examples can be used to learn more about how to
 develop an application with visualization and data processing with Traits
 and Mayavi:

 * :ref:`example_lorenz_ui`: A didactic and simple example that shows
   how the lorenz model can be integrated and visualized interactively
   while changing the model parameters.

 * :ref:`example_mayavi_traits_ui`: An example showing how you can mimic
   the UI of the Mayavi application with simple code using Traits.

 * :ref:`example_multiple_engines`: An example showing how you can
   isolate different scenes by affecting them to different engines.

 * :ref:`example_coil_design_application`: A full-blown and elaborate
   application enabling specification of a current-loop description for
   a coil, and integration of the resulting magnetic field with real-time
   visualization of the field and the coil structure.


Integrating in a WxPython application
--------------------------------------

Using the `Visualization` class defined above::

    import wx

    class MainWindow(wx.Frame):
        def __init__(self, parent, id):
            wx.Frame.__init__(self, parent, id, 'Mayavi in Wx')
            self.visualization = Visualization()
            self.control = self.visualization.edit_traits(parent=self,
                                    kind='subpanel').control
            self.Show()

    app = wx.PySimpleApp()
    frame = MainWindow(None, wx.ID_ANY)
    app.MainLoop()

Two examples of integrating Mayavi visualization with Wx applications are
given:

    * :ref:`example_wx_embedding`: a simple example, as above.
    * :ref:`example_wx_mayavi_embed_in_notebook`: a more complexe example,
      showing 2 different Mayavi views embedded in a Wx notebook.

.. _integrating_pyqt:

Integrating in a Qt application
----------------------------------

Mayavi dialogs can also be integrated in a PyQt or PySide application.

Before defining the `Visualization` class, you should set the toolkit
used by Traits to the Qt backend::

    import os
    os.environ['ETS_TOOLKIT'] = 'qt4'

Also, as Traits runs with PyQt and PySide, if you use PyQt, you must make
sure that you switch its binding in a mode that is compatible with PySide
(internal string representation mode), **before you import any PyQt
code**::

    import sip
    sip.setapi('QString', 2)

By default, with modern versions of the Enthought Tool Suite, Traits will
use PySide. To force the use of PyQt, you must set the QT_API environment
variable::

    os.environ['QT_API'] = 'pyqt'

Then using the visualization class defined above::

    from PyQt4 import QtGui

    class MainWindow(QtGui.QMainWindow):
        def __init__(self, parent=None):
            QtGui.QWidget.__init__(self, parent)
            self.visualization = Visualization()
            self.ui = self.visualization.edit_traits().control
            self.setCentralWidget(self.ui)

    window = MainWindow()
    window.show()
    QtGui.qApp.exec_()


For a full-blown example of embedding in Qt, see
:ref:`example_qt_embedding`.

.. warning::

    On definition of the model (and thus previous to the start of the
    event loop), Traits sets up some hooks on the main QApplication. As a
    result if you instanciate a new one, using for instance::

	app = QtGui.QApplication()

    Your Traits application will not work.


