Thanks Jeff. I didn't put path.translatemode(viz.CUBIC_BEZIER) in my code.
Yes, cubic_bezier mode has constant speed.
BTW, it's not bad for me to specify all positions of a animation path using bezier translation mode, but it is really hard to find positions in cubic_bezier translation mode. Having a cubic-bezier curve, do you have any easy way to get its intermediate points?
Thanks,
whj