Suppose we want to make a person walk back and forth from (-300,0) to (300,0), right behind the main characters. We'll use background controllers to accomplish this task.
First, define the walking animations. Say that the character's walking sprites are 10,0 through 10,3 and that they face to the right.
; Walk right
[Begin Action 10]
10,0,0,0,6
10,1,0,0,6
10,2,0,0,6
10,3,0,0,6
; Walk left
[Begin Action 11]
10,0,0,0,6,H
10,1,0,0,6,H
10,2,0,0,6,H
10,3,0,0,6,H
Now start the character off at the far left edge of his range.
[BGDef]
(...)
[BG Peregrinator]
type = anim
actionno = 10
id = 10
start = -300, 0
delta = 1,1
Let's give Peregrinator a comfortable ambling speed of 2 pixels per tick. The one-way distance for his walk is 600 pixels, which will take 300 ticks. In total, it'll take him 600 ticks to make the round trip. Using this knowledge, set up the background controllers appropriately: since the entire situation repeats every 600 ticks, we can set the global looptime to 600.
[BGCtrlDef Peregrinator]
; reset the whole deal every 600 ticks.
looptime = 600
ctrlID = 10
; Set velocity of 2 pixels/sec rightward at time 0.
[BGCtrl Walk Right]
type = VelSet
time = 0
x = 2
; Set velocity of 2 pixels/sec leftward at time 300.
[BGCtrl Walk Left]
type = VelSet
time = 300
x = -2
And that's it! You can make the walk look better by having Peregrinator slow down and display a turning animation at each end of his walk. This would entail use of the VelAdd and Anim controllers. If you want Peregrinator to stop and start at regular intervals as he goes from one end to the other, you could create more VelSet and Anim controllers with their own individual looptimes (to get the behavior to repeat at regular intervals).
