Physics Joints - Learn SpriteBuilder for iOS Game Development - page 313

This distance joint now allows absolutely no movement away from or toward its world
anchor. Even without the spring joint pulling on the spring, it will rest in place now. Give
it a try.
Caution You may be tempted to see how far you can take this. Try increasing
the spring joint's stiffness from 90 to 900, and reduce damping to 0. Don't for-
get to reset these values after the test! You'll notice the spring board will not be
entirely at rest, and if you touch it slightly, it will already and significantly push
the player upward. This may give you ideas, and perhaps you can use it for a
good effect, but really the point here is that very strongly opposing joints (and
the forces they impose on the connected bodies) add unrest and inaccuracies to
the physics simulation. Even potentially harmless-looking objects can suddenly
infuse other objects with high velocities even though they aren't moving much
by themselves.
Releasing the Spring Lock
With the lock in place, the spring is no longer usable. You'll need to create a
SpringBoard class to release the lock and then also put the lock back in place to reset
the springboard.
Select the springboard_spring node in Spring.ccb , and switch to the Item Code Connec-
tions tab. Enter SpringBoard as the custom class. Then switch to the Item Physics tab,
and enter spring in the Collision type field. This allows the GameScene class to imple-
ment a collision method that calls a SpringBoard method when the player touches the
springboard.
Now publish and open Xcode, but don't run the project just yet. First you have to create
another Objective-C class (by right-clicking the Source folder and selecting New File ).
Name the class SpringBoard , and be sure to make it a subclass of CCSprite because the
springboard_spring is a sprite.
Open the SpringBoard.h interface file. You only need to add a public method declaration
with which other objects can instruct the spring to let go of its lock. Add the code in List-
ing 9-1 to SpringBoard.h .
Listing 9-1 . The SpringBoard header declared the public letGo method