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# Draw a bunch of lines

This example demonstrates how multiple line-pieces can be drawn using one call, by discarding some fragments.

Note that this example uses canvas.context.X() to call gloo functions. These functions are also available as vispy.gloo.X(), but apply explicitly to the canvas.

Mouse wheel allows zooming in on the lines. Spacebar controls a timer that triggers rotation of the lines in 3D space.

    import numpy as np
    from vispy import gloo
    from vispy import app
    from vispy.util.transforms import perspective, translate, rotate

    W, H = 400, 400

    # Create vertices
    n = 100
    a_position = np.random.uniform(-1, 1, (n, 3)).astype(np.float32)
    a_id = np.random.randint(0, 30, (n, 1))
    a_id = np.sort(a_id, axis=0).astype(np.float32)

    VERT_SHADER = """
    uniform mat4 u_model;
    uniform mat4 u_view;
    uniform mat4 u_projection;
    attribute vec3 a_position;
    attribute float a_id;
    varying float v_id;
    void main (void) {
        v_id = a_id;
        gl_Position = u_projection * u_view * u_model * vec4(a_position,1.0);
    }
    """

    FRAG_SHADER = """
    varying float v_id;
    void main()
    {
        float f = fract(v_id);
        // The second useless test is needed on OSX 10.8
        if( (f > 0.0001) && (f < .9999) )
            discard;
        else
            gl_FragColor = vec4(0,0,0,1);
    }
    """

    class Canvas(app.Canvas):

        # ---------------------------------
        def __init__(self):
            app.Canvas.__init__(self, keys='interactive', size=(W, H))

            self.program = gloo.Program(VERT_SHADER, FRAG_SHADER)

            # Set uniform and attribute
            self.program['a_id'] = gloo.VertexBuffer(a_id)
            self.program['a_position'] = gloo.VertexBuffer(a_position)

            self.translate = 5
            self.view = translate((0, 0, -self.translate), dtype=np.float32)
            self.model = np.eye(4, dtype=np.float32)

            gloo.set_viewport(0, 0, self.physical_size[0], self.physical_size[1])
            self.projection = perspective(45.0, self.size[0] /
                                          float(self.size[1]), 1.0, 1000.0)
            self.program['u_projection'] = self.projection

            self.program['u_model'] = self.model
            self.program['u_view'] = self.view

            self.theta = 0
            self.phi = 0

            self.context.set_clear_color('white')
            self.context.set_state('translucent')

            self.timer = app.Timer('auto', connect=self.on_timer, start=True)

            self.show()

        # ---------------------------------
        def on_key_press(self, event):
            if event.text == ' ':
                if self.timer.running:
                    self.timer.stop()
                else:
                    self.timer.start()

        # ---------------------------------
        def on_timer(self, event):
            self.theta += .5
            self.phi += .5
            self.model = np.dot(rotate(self.theta, (0, 0, 1)),
                                rotate(self.phi, (0, 1, 0)))
            self.program['u_model'] = self.model
            self.update()

        # ---------------------------------
        def on_resize(self, event):
            gloo.set_viewport(0, 0, event.physical_size[0], event.physical_size[1])
            self.projection = perspective(45.0, event.size[0] /
                                          float(event.size[1]), 1.0, 1000.0)
            self.program['u_projection'] = self.projection

        # ---------------------------------
        def on_mouse_wheel(self, event):
            self.translate += event.delta[1]
            self.translate = max(2, self.translate)
            self.view = translate((0, 0, -self.translate))
            self.program['u_view'] = self.view
            self.update()

        # ---------------------------------
        def on_draw(self, event):
            self.context.clear()
            self.program.draw('line_strip')

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

Total running time of the script: (0 minutes 0.584 seconds)

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