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# Spatial Filtering

Example demonstrating spatial filtering using spatial-filters fragment shader.

Left and Right Arrow Keys toggle through available filters.

    import numpy as np

    from vispy.io import load_spatial_filters
    from vispy import gloo
    from vispy import app
    from vispy.util.logs import set_log_level
    # turn off INFO messages, see PR #1363
    # Some shader compilers will optimize out the 'u_shape' and 'u_kernel'
    # uniforms for the Nearest filter since they are unused, resulting in
    # an INFO message about them not being active
    set_log_level('warning')

    # create 5x5 matrix with border pixels 0, center pixels 1
    # and other pixels 0.5
    img_array = np.zeros(25).reshape((5, 5)).astype(np.float32)
    img_array[1:4, 1::2] = 0.5
    img_array[1::2, 2] = 0.5
    img_array[2, 2] = 1.0

    # loading interpolation kernel
    kernel, names = load_spatial_filters()
    names = [name + '2D' for name in names]

    # A simple texture quad
    data = np.zeros(4, dtype=[('a_position', np.float32, 2),
                              ('a_texcoord', np.float32, 2)])
    data['a_position'] = np.array([[-1, -1], [+1, -1], [-1, +1], [+1, +1]])
    data['a_texcoord'] = np.array([[1, 0], [1, 1], [0, 0], [0, 1]])

    VERT_SHADER = """
    // Attributes
    attribute vec2 a_position;
    attribute vec2 a_texcoord;

    // Varyings
    varying vec2 v_texcoord;

    // Main
    void main (void)
    {
        v_texcoord = a_texcoord;
        gl_Position = vec4(a_position,0.0,1.0);
    }
    """

    FRAG_SHADER = """
    #include "misc/spatial-filters.frag"
    uniform sampler2D u_texture;
    uniform vec2      u_shape;
    varying vec2      v_texcoord;
    void main()
    {
        gl_FragColor = %s(u_texture, u_shape, v_texcoord);
    }

    """

    class Canvas(app.Canvas):

        def __init__(self):
            app.Canvas.__init__(self, keys='interactive', size=((512), (512)))

            self.program = gloo.Program(VERT_SHADER, FRAG_SHADER % 'Nearest2D')
            self.texture = gloo.Texture2D(img_array, interpolation='nearest')

            # using packed data as discussed in pr #1069
            self.kernel = gloo.Texture2D(kernel, interpolation='nearest')
            self.program['u_texture'] = self.texture
            self.program['u_shape'] = img_array.shape[1], img_array.shape[0]
            self.program['u_kernel'] = self.kernel

            self.names = names
            self.filter = 16
            self.title = 'Spatial Filtering using %s Filter' % \
                         self.names[self.filter]

            self.program.bind(gloo.VertexBuffer(data))

            self.context.set_clear_color('white')
            self.context.set_viewport(0, 0, 512, 512)
            self.show()

        def on_key_press(self, event):
            if event.key in ['Left', 'Right']:
                if event.key == 'Right':
                    step = 1
                else:
                    step = -1
                self.filter = (self.filter + step) % 17
                self.program.set_shaders(VERT_SHADER,
                                         FRAG_SHADER % self.names[self.filter])

                self.title = 'Spatial Filtering using %s Filter' % \
                             self.names[self.filter]
                self.update()

        def on_resize(self, event):
            self.context.set_viewport(0, 0, *event.physical_size)

        def on_draw(self, event):
            self.context.clear(color=True, depth=True)
            self.program.draw('triangle_strip')

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

Total running time of the script: (0 minutes 0.872 seconds)

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