Sequences, Parallels & Intervals: Rock your Panda

in Panda3D, a Sequence is a list of ‘actions’ to be executed in order. Each action in the sequence is executed once and waits for the previous action to finish.

s=Sequence(a,b,c,name="NAME") # to create a sequence
s.play() # play once
s.loop() # play over and over
s.stop() # I'm making this up

Typically, a sequence consists in Intervals. The Panda3D manual has a large chapter dedicated to Intervals. Meanwhile, the Actor class provides easy methods to define intervals for position (pos), rotation (hpr) and scale (scale!).
An interval changes a property (location, rotation, scale, color…) at every frame until that property reaches a specified target value. As you can see, an optional start value can be defined for the property we are interpolating.

Actor
  posInterval(seconds,Point3(x,y,z), [start=Point3(x0,y0,z0)])
  hprInterval(seconds,Vec3(x,y,z)) # in degrees, e.g (180,0,0)
  scaleInterval(...)
  posHprInterval(...)
  posScaleInterval(...)
  hprScaleInterval(...)
  posHprScaleInterval(...)

A Parallel uses the same syntax as a sequence. With a parallel, actions are executed in… parallel.

Import statements

# I want to use sequences and parallels
from direct.interval.IntervalGlobal import *
# I have an actor that I want to move around/rotate
from direct.actor import Actor #use actor methods

Wait a second, is that all?

You may have guessed that Sequence and Parallel inherit from Interval. This allows generating complex, hierarchic sequences.

Sometimes we just need to yield a little bit before playing a sound or doing over things. The Wait interval does just that.

w=Wait(seconds) # defines a 'pause' in a sequence

Finally, the Func interval, lets us call any function as part of a sequence:

f=Func(function[,arg1[,arg2[,...]]])

Use and abuse?

Animation is an art, and you’ll find much more in the Panda3D manual, in the meantime, there’s a couple of points worth raising:

• Where a complex animation is not very interactive, it may not be worth programming at all. What are animation packages for?
• If your animation is very dynamic, consider updating your objects directly using a task (see previous article). Say you were programming boids. How much should we rely on intervals, and how much on intervals and sequences?

That’s it for now.

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