Physics Joints - Learn SpriteBuilder for iOS Game Development - page 311

lower horizontal collision segment should be almost parallel to the horizontal axis. (See
Figure 9-22 . )
Figure 9-22 . The springstopper's collision shape
The springstopper is supposed to suddenly prevent the spring from expanding any further.
It ought to keep the spring in its shaft so that it can't move to the side, and it gives the im-
pression of a spring that is actually extending upward due to actual spring force rather
than being pulled from the outside.
Before you can test this, you have to select the springboard_spring . On the Item Physics
tab, enter spring in the Categories field and enter springstopper, player, obstacle in the
Masks field. This will make the spring the only body that will collide with the springstop-
per.
To ensure collisions with the player continue to work, you also have to open Player.ccb
and then add spring to the player sprite's Masks field so that it contains the following la-
bels: trigger, border, obstacle, spring .
And if you want the spring to collide with the chains and ropes, you'll have to edit
Chain.ccb and Rope.ccb in order to add spring to each physics body's Masks field.