Technical Deep Dive into the New Prefab System
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Take a dive deep into the new prefab features. What's the inside versus outside of a prefab? How does it relate to Prefab mode, overrides, unpacking, and prefab variants? How has the new prefab back-end changed? This session will give you a better understanding of the Prefab system, the pros and cons of various implementation decisions, and some aha moments working with Prefab nesting. Speakers: Steen Lund & Rune Skovbo Johansen (Unity) https://unite.unity.com/2018/berlin
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Technical Deep Dive into the New Prefab System
- 1. GenerativeArt–MadewithUnity Technical Deep Dive into the New Prefabs System 1
- 2. 2 Rune Skovbo JohansenSteen Lund
- 3. Agenda 3 ● Prefab Assets, Instances and Content ● Prefab Importing ● Prefab Mode ● Nesting and Overrides at Multiple Levels ● Unpacking & Simple Refactoring
- 4. Takeaway 4 ● Knowledge of how the backend works ● Changes to Unity’s handling of Prefabs assets ● Understanding the implications of nesting and overrides ● Tricks for working with Variant inheritance
- 5. Prefab Assets, Instances and Content 5
- 7. 7 Make GameObject into Prefab instance
- 8. 8 Create overrides on Prefab instance
- 11. 11 Prefab AssetScene Apply to Prefab Asset
- 12. 12 Prefab AssetScene Apply to Prefab Asset
- 14. 14 Prefab Variants CatScene Cat (instance of Animal) Cat Animal Animal
- 15. What is a Prefab 15 Instance?
- 16. 16 PrefabInstance Handle Instance Leg Table More than you see with the naked eye
- 17. 17 Prefabs in Scene files Main Camera Directional Light Scene File PrefabInstance Handle Loaded Scene PrefabInstance Handle
- 18. What is a Prefab Asset? 18 Prefab File Table Leg
- 19. 19 Consider a Prefab Asset being a scene Prefab File Table Leg PrefabInstance Handle
- 21. 21 Prefab File in Assets Folder Prefab Importer Table Leg Prefab File in Library Folder Prefab Asset Handle Table Leg
- 22. 22 Prefab File in Assets Folder Prefab File in Library Folder Prefab Importer Table Leg PrefabInstance Handle Prefab Asset Handle Table Leg Vase PrefabInstance Handle
- 23. 23 Prefab Variant File in Assets Folder Prefab File in Library Folder Prefab Importer PrefabInstance Handle Prefab Asset Handle Vase PrefabInstance Handle
- 24. 24 Dependency chain Prefab Importer Prefab Importer Inner Middle Outer
- 25. 25 Build size implications ● No change for Scene, have always been baked out at build time ● Resources and AssetBundles are affected AA A B C
- 26. 26 PrefabAsset Handle PrefabInstance Handle Asset in Library FolderPrefab Instance Table LegLeg Table VaseVase PrefabInstance Handle
- 27. Prefab Mode 27
- 28. 28 Edit Prefab in Prefab Mode
- 29. Prefab Mode Editing Prefab Asset content not Prefab instance GameObject icon not Prefab icon Saving not applying 29
- 30. 30 Prefab Asset Prefab instance Prefab contents in Prefab Mode automatic update apply open from instance open from asset save
- 33. Multiple Levels of Corresponding Objects 33 Instance AssetInstance of instance
- 34. Corresponding Objects with Nesting 34 Table LegLeg Table VaseVase Vase TableScene Vase
- 35. Corresponding Objects with Variants 35 CatCat Animal CatScene Animal
- 37. 37 A Prefab instance can have overrides
- 38. 38 A nested/base Prefab instance can also have overrides
- 39. 39 An instance of the outer Prefab can also have overrides
- 40. 40 Overrides can exist at every level except innermost
- 41. 41
- 42. Apply to outer Prefab 42
- 43. 43 Outer InnerScene Apply as Override in Prefab ‘Outer’
- 44. 44 Outer InnerScene Apply as Override in Prefab ‘Outer’
- 45. Apply to inner Prefab 45
- 46. 46 Outer InnerScene Apply to Prefab ‘Inner’
- 47. 47 Outer InnerScene Apply to Prefab ‘Inner’
- 48. 48 Outer InnerScene Apply to Prefab ‘Inner’
- 49. 49 Outer InnerScene Apply to Prefab ‘Inner’
- 50. Apply to inner Prefab when outer has override 50
- 51. 51 Scene Outer Inner Apply to Prefab ‘Inner’ 51
- 52. 52 Scene Outer Inner Apply to Prefab ‘Inner’ 52
- 53. 53 Scene Outer Inner Apply to Prefab ‘Inner’ 53
- 54. 54 Scene Outer Inner Apply to Prefab ‘Inner’ 54
- 55. Unpacking 55
- 56. 56 Prefabs can no longer be disconnected
- 57. 57
- 58. 58 Make Prefab instance into GameObject Unpack Prefab Contents (one layer)
- 59. 59 Make Prefab instance into GameObject Unpack Prefab Contents (one layer) Prefab Variant becomes its base
- 60. 60
- 62. Make Existing Prefab into Variant 62 CatCat How to make Cat Prefab a Variant of a new Animal Prefab? CatScene
- 63. Make Existing Prefab into Variant 63 CatCat Make into Prefab called Animal CatScene
- 64. Make Existing Prefab into Variant 64 CatCat Animal Make into Prefab called Animal ✓ CatScene Animal
- 65. Make Existing Prefab into Variant 65 CatCat Animal Make into Prefab called Animal ✓ Cat (Variant)Scene Animal
- 66. 66 and now in reverse
- 67. Make Prefab Variant into Regular Prefab 67 CatCat Animal How to make Cat Prefab no longer a Variant of Animal Prefab? CatScene Animal
- 68. Make Prefab Variant into Regular Prefab 68 CatCat Animal Unpack Prefab CatScene Animal
- 69. Make Prefab Variant into Regular Prefab 69 CatCat Animal Unpack Prefab ✓ CatScene Animal
- 70. 70 Can you make a Prefab a Variant of an existing other Prefab? No, that’s not simple…
- 72. Insert New Prefab in Inheritance Chain 72 CatCat Animal How to insert new Mammal Prefab between Cat and Animal? CatScene Animal
- 73. Insert New Prefab in Inheritance Chain 73 CatCat Animal Make into Prefab called Mammal CatScene Animal
- 74. Insert New Prefab in Inheritance Chain 74 CatCat Animal Make into Prefab called Mammal ✓ Mammal CatScene Mammal Animal
- 75. 75 and now in reverse
- 76. Remove Prefab from Inheritance Chain 76 CatCat AnimalMammal How to make Cat Prefab inherit directly from Animal? CatScene Mammal Animal
- 77. Remove Prefab from Inheritance Chain 77 CatCat AnimalMammal Unpack Prefab CatScene Mammal Animal
- 78. Remove Prefab from Inheritance Chain 78 CatCat AnimalMammal Unpack Prefab ✓ CatScene Mammal Animal
Editor's Notes
- The PrefabInstance handle is a little more than a handle as it hold information about the location in the Transform hierarchy, List of overrides and deleted Components and a reference back to the Prefab asset it came from
- On the Left: Basically a scene file looks like this, there are two GameObject and a PrefabInstance object representing a prefab On the right: This expands into all GameObjects when loaded plus the PrefabInstance in memory mentioned on previously
- Basically just a collection of GameObject … Notice the similarity to a scene file
- Imagine for a moment if prefabs themselves could simply have a PrefabInstance object inside them that would expand into GameObjects when loaded But in order to do this we need to change the handling of Prefab in Unity a little
- Previous versions of Unity would read the Prefab file directly from the Assets folder, no importing was going on except some registration of the file
- The importer reads the prefab file, processes it and writes the hierarchy back to the Library folder The importer writes a little more then just the hierarchy A PrefabAssetHandle is also written to the Library folder All objects in the Library folder file points to the Prefab asset handle This is for internal use so we can track which Prefab Asset an object belongs to.
- The importer read the PrefabInstance handle, expands it and applies overrides, before writing the full hierarchy plus Prefab Instance handle to the Library folder
- Variant is similar to nesting but is simply at the root of the Prefab
- Performance implications, as a saving the inner prefab can spawn a series of imports which can feel slow depending on depth and size of prefab
- Does not change anything for scene as they have always been baked out at build time If Prefab A is nested inside, Prefab B, and Prefab C, A is in the build 3 times, on its own, in B and in C. Luckily GameObjects don’t take up much space, but it is still something to be aware of
- Now the fundamentals are in place lets examine some more advanced use cases