Physics Joints - Learn SpriteBuilder for iOS Game Development - page 320

Thus far, I have neglected the properties related to breaking joints and adding torque. I
know they can be very intriguing, so let's quickly try them on the chain and rope.
Breaking Force Example
Open Chain.ccb , and select the joint that connects the last chain segment with the ball.
This is most likely the last CCPhysicsPivotJoint instance in the Timeline.
The Breaking force field on the Item Properties tab is set to a stress threshold that the
joint is able to withstand. If the joint stress exceeds the arbitrary value entered in Breaking
force , the joint will be removed. Change the radio button next to Breaking force so that
you can enter a value in the text field next to it. As for the value, enter 1060 . If you ask
me how I determined that value: trial and error. It should work if you change the joint
properties as instructed; otherwise, you may find you need to use a higher or lower
value—see the following discussion.
Caution Max force must be either unlimited or set to a value equal to or higher
than Breaking force .
Try this in the game with a chain instance whose rotation is 0 so that it does not swing.
Swinging alone might cause the breaking force to be exceeded, because even just a
slightly lower Breaking force value of 1050 would always sever the connection. If you get
this right, merely touching the ball or chain with the player will cause the joint to disap-
pear, and the ball will drop from the chain.
Now there's a problem here. The Breaking force setting is not very reliable and thus not
suitable for triggered events that have to happen. For instance, if touching the ball should
always drop it, you should implement a collision method rather than using collision types.
Breaking force is also tedious to determine, but it's not impossible to determine it if you
follow this principle:
Enter an arbitrary high value for Breaking force , say, 100 .
Check if the joint in question breaks. Ideally, the joint bodies should be at
rest.
If the joint breaks, double the value and try again.