For more detail this asset from the Unity Asset Store: Click Here
This is a paid asset, but now you can download Pool, Trigger, Constrain Bundle for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Pool, Trigger, Constrain Bundle v7.1.0
“If possible, please buy the package to support the developer”
New pricing from March 2016! Was $59.95. May not be a permanent change. Save over 25% with this bundle of core, high-performance tools and get your 2D or 3D prototype up and running in no time, and scale to full production without hassle.
* PoolManager: Preload and pool objects for re-use with PoolManager, the most popular and battle hardened Instance pooling solution.
* TriggerEventPRO: Get easy access and information to and from objects in range of other objects and construct behaviors using components and events with this robust framework.
* UnityConstraints: Drop on simple behaviors, such as Smooth Look-At (use any axis), Billboard to camera and Transform (like parenting without the hierarchy) constraints with UnityConstraints.
If you were to buy these individually, it would cost $80.
Features, Documentation & Videos:
packages.path-o-logical.com
