.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/gloo/geometry_shader.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

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

        :ref:`Go to the end <sphx_glr_download_gallery_gloo_geometry_shader.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_gloo_geometry_shader.py:


Use a Geometry Shader
=====================

Simple geometry shader: Takes one point as input emits one triangle as output.

NOTE: This example is currently not processed in CI.

.. GENERATED FROM PYTHON SOURCE LINES 15-95



.. image-sg:: /gallery/gloo/images/sphx_glr_geometry_shader_001.png
   :alt: geometry shader
   :srcset: /gallery/gloo/images/sphx_glr_geometry_shader_001.png
   :class: sphx-glr-single-img





.. code-block:: Python


    import numpy as np
    from vispy import gloo
    from vispy import app

    # geometry shaders require full OpenGL namespace provided by PyOpenGL
    gloo.gl.use_gl('gl+')


    position = np.random.normal(loc=0, scale=0.3, size=(1000, 2)).astype('float32')


    VERT_SHADER = """
    #version 330

    in vec2 a_position;

    void main (void) {
        gl_Position = vec4(a_position, 0, 1);
        gl_PointSize = 3.0;
    }
    """


    GEOM_SHADER = """
    #version 330

    layout (points) in;
    layout (triangle_strip, max_vertices=3) out;

    void main(void) {
        vec4 p = gl_in[0].gl_Position;
    
        gl_Position = p;
        EmitVertex();
        gl_Position = p + vec4(0.06, 0.03, 0, 0);
        EmitVertex();
        gl_Position = p + vec4(0.03, 0.06, 0, 0);
        EmitVertex();
        EndPrimitive();
    }
    """


    FRAG_SHADER = """
    #version 330

    out vec4 frag_color;

    void main()
    {
        frag_color = vec4(0,0,0,0.5);
    }
    """


    class Canvas(app.Canvas):
        def __init__(self):
            app.Canvas.__init__(self, keys='interactive', size=(400, 400))
            self.program = gloo.Program()
            self.program.set_shaders(vert=VERT_SHADER, geom=GEOM_SHADER,
                                     frag=FRAG_SHADER)
            self.program['a_position'] = gloo.VertexBuffer(position)
            gloo.set_viewport(0, 0, self.physical_size[0], self.physical_size[1])
            self.context.set_clear_color('white')
            self.context.set_state('translucent', cull_face=False,
                                   depth_test=False)
            self.show()

        def on_resize(self, event):
            gloo.set_viewport(0, 0, event.physical_size[0], event.physical_size[1])

        def on_draw(self, event):
            self.context.clear()
            self.program.draw('points')


    if __name__ == '__main__':
        canvas = Canvas()
        app.run()


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

   **Total running time of the script:** (0 minutes 0.448 seconds)


.. _sphx_glr_download_gallery_gloo_geometry_shader.py:

.. only:: html

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

    .. container:: sphx-glr-download sphx-glr-download-jupyter

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

    .. container:: sphx-glr-download sphx-glr-download-python

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

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: geometry_shader.zip <geometry_shader.zip>`


.. only:: html

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

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