Physics Joints - Learn SpriteBuilder for iOS Game Development - page 308

Designing a shaft with a single body may be a little unusual at first because you have to
trace both the inner and outer walls of the shaft. Here's a trick that makes this less confus-
ing: from the initial rectangular polygon, drag the two bottom-most points down, several
points past the bottom of the spring. Now you can carve out the shaft more easily. Again,
10 points should suffice. (See Figure 9-19 for reference.)
Figure 9-19 . The springboard's shaft collision shape
The tricky part here is to design the shaft as straight as possible while making it just
slightly larger than the springboard's bolt shape. After all, the spring is supposed to move
unhindered up and down in the shaft, while its sideward movement should be restricted as
much as possible by the shaft. Figure 9-20 shows both collision shapes overlaid, using ad-
vanced image-processing technology (an artist did it).
Figure 9-20 . Shaft and bolt collision shapes rendered in the same image
Tip If you want to test the overlap quickly, collapse the springboard_spring in
the Timeline so that its child nodes are hidden. With either node selected in the
Timeline, you can use the up and down arrows to quickly select the other node,