Physics Joints - Learn SpriteBuilder for iOS Game Development - page 292

Creating a Rope
How to create a physics rope is a frequently asked question, yet the solution is not nearly
as complex as you might imagine. In fact, if you observed the behavior of the chain, you
may have noticed that it isn't too far from how a physics-simulated rope should behave.
Turning the Chain into a Rope
In fact, you're just going to modify the chain to make a rope. To do so, create a duplicate
of Chain.ccb and rename it to Rope.ccb .
Note If SpriteBuilder has no duplication functionality yet, you can make a
copy with Finder. Locate the project's .spritebuilder folder and browse into the
SpriteBuilder Resources/Prefabs folder in order to make a duplicate of the
Chain.ccb . You should then rename the duplicate to Rope.ccb . In SpriteBuild-
er's File View , the Rope.ccb should automatically appear in the Prefabs folder.
Open the Rope.ccb . Several modifications to the chain are necessary to turn it into a rope.
First, select all the chain2 sprites, and on the Item Properties tab, change their Sprite
frame to SpriteSheets/GameElements/chainball_chain1.png in order to replace the
8-shaped chain elements with the l-shaped ones. This step is added only to improve the
visual appearance of the rope.
Because changing the sprite frames also changes the locations of the pivot joints, you
should select the joints that are offset from the rope and change their anchor to 6.5x4 so
that all pivot joints are on the rope and spaced evenly. Also, if you switch to the Item
Physics tab and select the former chain2 sprites, you'll notice their collision shape is too
big for the image. So you should also edit the collision shape to more closely match the
chain1 images that you are using as rope segments.
Also, change the Scale property of the ball to 0.5x0.5 to make it smaller. Change its Y po-
sition to -156 to make it connect with the rope. And, on the Item Physics tab, change its
density to 0.15 to make the ball lighter. These new settings will reduce stress on the rope
and allow it to swing more easily.
The former chain segments will feel more like a rope if you tweak the joints so that the
spring is enabled and the angle limit is smaller than before. Perform the following steps