.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_auto_tutorials_04_shaders_viz_shader.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_auto_tutorials_04_shaders_viz_shader.py:


=============
Varying Color
=============

This example shows how to use shaders to generate a shaded output. We will
demonstrate how to load polydata then use a custom shader calls to render
a custom shaded model.
First, a bunch of imports.


.. code-block:: default


    from fury import window, ui, io, utils
    from fury.shaders import shader_to_actor, add_shader_callback







Let's download  and load the model


.. code-block:: default


    from fury.data.fetcher import fetch_viz_models, read_viz_models
    fetch_viz_models()
    model = read_viz_models('utah.obj')






.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    Dataset is already in place. If you want to fetch it again please first remove the folder /Users/koudoro/.fury/models 



Let's start by loading the polydata of choice.
For this example we use the standard utah teapot model.
currently supported formats include OBJ, VKT, FIB, PLY, STL and XML


.. code-block:: default


    utah = io.load_polydata(model)
    utah = utils.get_polymapper_from_polydata(utah)
    utah = utils.get_actor_from_polymapper(utah)
    mapper = utah.GetMapper()








To change the default shader we add a shader replacement.
Specify vertex shader using vtkShader.Vertex
Specify fragment shader using vtkShader.Fragment


.. code-block:: default

    vertex_shader_code_decl = \
        """
        out vec4 myVertexVC;
        """

    vertex_shader_code_impl = \
        """
        myVertexVC = vertexMC;
        """

    fragment_shader_code_decl = \
        """
        uniform float time;
        out vec4 myVertexVC;
        """

    fragment_shader_code_impl = \
        """
        vec2 iResolution = vec2(1024,720);
        vec2 uv = myVertexVC.xy/iResolution;
        vec3 col = 0.5 + 0.5 * cos((time/30) + uv.xyx + vec3(0, 2, 4));
        fragOutput0 = vec4(col, 1.0);
        """

    shader_to_actor(utah, "vertex", impl_code=vertex_shader_code_impl,
                    decl_code=vertex_shader_code_decl)
    shader_to_actor(utah, "fragment", decl_code=fragment_shader_code_decl)
    shader_to_actor(utah, "fragment", impl_code=fragment_shader_code_impl,
                    block="light")







Let's create a scene.


.. code-block:: default


    scene = window.Scene()

    global timer
    timer = 0







The timer will call this user defined callback every 30 milliseconds.


.. code-block:: default



    def timer_callback(obj, event):
        global timer
        timer += 1.0
        showm.render()
        scene.azimuth(5)








The shader callback will update the color of our utah pot via the update of
the timer variable.


.. code-block:: default


    def shader_callback(_caller, _event, calldata=None):
        program = calldata
        global timer
        if program is not None:
            try:
                program.SetUniformf("time", timer)
            except ValueError:
                pass


    add_shader_callback(utah, shader_callback)






Let's add a textblock to the scene with a custom message


.. code-block:: default


    tb = ui.TextBlock2D()
    tb.message = "Hello Shaders"







Change the property of the actor


.. code-block:: default


    utah.GetProperty().SetOpacity(0.5)







Show Manager

Now that all the elements have been initialised, we add them to the show
manager.


.. code-block:: default


    current_size = (1024, 720)
    showm = window.ShowManager(scene, size=current_size, reset_camera=False)

    showm.initialize()
    showm.add_timer_callback(True, 30, timer_callback)

    scene.add(utah)
    scene.add(tb)

    interactive = False
    if interactive:
        showm.start()

    window.record(showm.scene, size=current_size, out_path="viz_shader.png")



.. image:: /auto_tutorials/04_shaders/images/sphx_glr_viz_shader_001.png
    :class: sphx-glr-single-img





.. rst-class:: sphx-glr-timing

   **Total running time of the script:** ( 0 minutes  0.177 seconds)


.. _sphx_glr_download_auto_tutorials_04_shaders_viz_shader.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: viz_shader.py <viz_shader.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: viz_shader.ipynb <viz_shader.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_