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I have a scene with a massive terrain. It took a long time to load (approximately 60 seconds) when I pressed play. I am in the editor.
I prefabbed it.
Now it only took about 5 seconds to load when I pressed play. Why?
My best guess is that there is some preloading done when it is prefabbed, but it only takes a few seconds to prefab it. So that couldn't be the reason. Any ideas? I am at a loss.
The Unity Documentation for Prefabs simply describes it as
A template from which you can create new object instances in the scene. Any edits made to a prefab asset are immediately reflected in all instances produced from it but you can also override components and settings for each instance individually.
My experience tells, it does not. Since google does not point to any rigid analysis that whether or not prefabs improve performance nor I have done any experimentation regarding this, this Unity answers.com question explains it like this:
There's nothing magic about prefabs; they are simply a convenience. There's no performance difference between putting two cubes in a scene, or making a prefab out of the cube and then putting two cube prefabs in the scene.
That's all. If there is any performance improvement reports or analysis or anything regarding this, I might want to know about it as well. Thank you.
EDIT: I tried what you said, made a terrain of 50k by 50k with heightmap resolution of 512 (couldn't get any higher).
Time difference was not significant but here's what I noticed. Whenever you change Terrain settings, on the bottom right corner, there is some processing happening. If you let that complete, the startup time would decrease.
Here's what it looks like:
I didn't know your terrain settings and how complex it was but from this I can deduce that bottom-right processing might be the thing that manages the load time. It might be loading in the memory and could be doing some one-time calculations/ processing.
So the original question "why do prefabs speedup loading" is an very interessting question.
You may check out the memory part of the profiler when working with prefabs.
Every asset you once prefabed will use memory for reference. Even when you unload and destroy the prefab - there is still some information kept in the memory (as an example the texture part of the prefab).
When you load the prefab unity will access this information by reference and speedup loading.
When your project getting very large though it could eat up your memory even when you destroy thous prefabs. This also applies to prefabs whch are currently not loaded into scene.
You should check out Unitys Addressable Asset for qualified information.
Greetings :)
additive to others answers. we have flyweight pattern that is concerned with memory and optimization. when you have lots of objects, flyweight pattern, shares the same data in same memory and allocates memory for new or different features. unity3d uses this pattern to work with prefabs.
other approach is in programming, cloning is much faster with less allocation than making whole new object. in c# its MemberWiseClone and its instantiate in Unity
Prefab is just for reusability and for a repeatable task it doesn't have any connection with preprocessing. When rendering process happens with any game objects and it has any retrace to the project panel unity make its meta file and store some information on it and for next time Unity uses that information for next time.
