最新Unity DOTS教程之BlobAsset核心机制分析

最近DOTS发布了正式的版本, 我们来分享一下DOTS里面BlobAsset机制，方便大家上手学习掌握Unity DOTS开发。

BlobAsset 概叙

DOTS提供了BlobAsset机制来把数据生成高效的二进制数据。BlobAsset的数据是不可变的。BlobAsset只支持非托管类型数据。支持Burst编译器编译出来的类型。同时它只存储非托管类型的数据，这样使得它序列化与反序列化的性能与效率非常的块。BlobAsset也可以被entity种的component使用。

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BlobAsset不支持如:数组, string等其它的托管对象(垃圾回收器可以回收的为托管对象),而且运行的时候不允许改变里面的数据内容。BlobAsset为了更快的加载,他只会包含传值的类型，不能包含对内部的引用与内部指针。BlobAsset除了支持标准的值类型(float, int等)以外它还支持三种特殊的类型: BlobArray, BlobPtr, BlobString。如果BlobAsest包含内部指针，编译器会报错。使用BlobAsset主要注意以下几个方面:

A: 创建一个BlobAsset,你需要先生成一个BlobBuilder,来帮助你处理计算每个数据在内存种的偏移;

总结：使用BlobBuilder来生成BlobAsset,基于BlobAssetReference来高效访问里面的数据。

BlobAsset的创建与使用

创建一个BlobAsset,按照以下步骤来进行处理即可:

BlobBuilder构造出BlobAsset,并把数据存入进去，然后再生成BlobAssetReference<T>来给用户操作数据。参考代码如下:

 struct MarketData
 {
 public float PriceOranges;
 public float PriceApples;
 }
 BlobAssetReference<MarketData> CreateMarketData()
 {
 // Create a new builder that will use temporary memory to construct the blob asset
 var builder = new BlobBuilder(Allocator.Temp);
 // Construct the root object for the blob asset. Notice the use of `ref`.
 ref MarketData marketData = ref builder.ConstructRoot<MarketData>();
 // Now fill the constructed root with the data:
 // Apples compare to Oranges in the universally accepted ratio of 2 : 1 .
 marketData.PriceApples = 2f;
 marketData.PriceOranges = 4f;
 // Now copy the data from the builder into its final place, which will
 // use the persistent allocator
 var result = builder.CreateBlobAssetReference<MarketData>(Allocator.Persistent);
 // Make sure to dispose the builder itself so all internal memory is disposed.
 builder.Dispose();
 return result;
 }
 #endregion

如果你要存数组到BlobAsset,可以使用BlobArray来处理。数组数据内部基于索引的偏移来进行每个元素的定位。将数组存入到BlobAsset的代码如下:

 #region CreateBlobAssetWithArray
 struct Hobby
 {
 public float Excitement;
 public int NumOrangesRequired;
 }
 struct HobbyPool
 {
 public BlobArray<Hobby> Hobbies;
 }
 BlobAssetReference<HobbyPool> CreateHobbyPool()
 {
 var builder = new BlobBuilder(Allocator.Temp);
 ref HobbyPool hobbyPool = ref builder.ConstructRoot<HobbyPool>();
 // Allocate enough room for two hobbies in the pool. Use the returned BlobBuilderArray
 // to fill in the data.
 const int numHobbies = 2;
 BlobBuilderArray<Hobby> arrayBuilder = builder.Allocate(
 ref hobbyPool.Hobbies,
 numHobbies
 );
 // Initialize the hobbies.
 // An exciting hobby that consumes a lot of oranges.
 arrayBuilder[0] = new Hobby
 {
 Excitement = 1,
 NumOrangesRequired = 7
 };
 // A less exciting hobby that conserves oranges.
 arrayBuilder[1] = new Hobby
 {
 Excitement = 0.2f,
 NumOrangesRequired = 2
 };
 var result = builder.CreateBlobAssetReference<HobbyPool>(Allocator.Persistent);
 builder.Dispose();
 return result;
 }
 #endregion

存储string到BlobAsset, 代码如下:

#region CreateBlobAssetWithString
 struct CharacterSetup
 {
 public float Loveliness;
 public BlobString Name;
 }
 BlobAssetReference<CharacterSetup> CreateCharacterSetup(string name)
 {
 var builder = new BlobBuilder(Allocator.Temp);
 ref CharacterSetup character = ref builder.ConstructRoot<CharacterSetup>();
 character.Loveliness = 9001; // it's just a very lovely character
 // Create a new BlobString and set it to the given name.
 builder.AllocateString(ref character.Name, name);
 var result = builder.CreateBlobAssetReference<CharacterSetup>(Allocator.Persistent);
 builder.Dispose();
 return result;
 }
 #endregion

存储BlobPtr数据到BlobAsset，代码如下:

#region CreateBlobAssetWithInternalPointer
 struct FriendList
 {
 public BlobPtr<BlobString> BestFriend;
 public BlobArray<BlobString> Friends;
 }
 BlobAssetReference<FriendList> CreateFriendList()
 {
 var builder = new BlobBuilder(Allocator.Temp);
 ref FriendList friendList = ref builder.ConstructRoot<FriendList>();
 const int numFriends = 3;
 var arrayBuilder = builder.Allocate(ref friendList.Friends, numFriends);
 builder.AllocateString(ref arrayBuilder[0], "Alice");
 builder.AllocateString(ref arrayBuilder[1], "Bob");
 builder.AllocateString(ref arrayBuilder[2], "Joachim");
 // Set the best friend pointer to point to the second array element.
 builder.SetPointer(ref friendList.BestFriend, ref arrayBuilder[2]);
 var result = builder.CreateBlobAssetReference<FriendList>(Allocator.Persistent);
 builder.Dispose();
 return result;
 }
 #endregion

这里的BlobPtr是基于数据的偏移来存储的;

今天的BlobAsset机制，就给大家分享到这里了，更多的DOTS系列，关注我们,持续更新！