The following example demonstrates the use of a clutter.BehaviourPath with a simple custom alpha callback. This simply moves the rectangle from the top-left to the bottom-right of the canvas at constant speed:

Source Code

File: main.py

import sys

import clutter


# This must return a value between 0 and 1.0
# This will be called as many times per seconds as specified in our call to
# clutter.Timeline.
def on_alpha(alpha, data):
    # Get the position in the timeline,
    # so we can base our value upon it
    timeline = alpha.get_timeline()
    return timeline.get_progress()


def main():
    stage_color = clutter.Color(0, 0, 0, 255)
    rect_color = clutter.Color(255, 255, 255, 153)

    # Get the stage and set its size and color
    stage = clutter.Stage()
    stage.set_size(200, 200)
    stage.set_color(stage_color)

    # Add a rectangle to the stage
    rect = clutter.Rectangle(rect_color)
    rect.set_size(40, 40)
    rect.set_position(10, 10)
    stage.add(rect)
    rect.show()

    # Show the stage
    stage.connect('destroy', clutter.main_quit)
    stage.show()

    timeline = clutter.Timeline(5000) # milliseconds
    timeline.set_loop(True)
    timeline.start()

    # Instead of our custom callback,
    # we could use a standard callback. For instance, CLUTTER_ALPHA_SINE_INC.
    alpha = clutter.Alpha(timeline)
    alpha.set_func(on_alpha, None)

    behaviour = clutter.BehaviourPath(alpha, knots=((10, 10), (150, 150)))
    behaviour.apply(rect)

    # Start the main loop, so we can respond to events
    clutter.main()

    return 0


if __name__ == '__main__':
    sys.exit(main())