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;
• B: 当你要使用一个BlobAsset的时候你需要使用ref BlobAssetReference, 来访问BlobAsset种的数据，这样访问数据的时候是基于BlobAsset内部引用的不会有值的copy;

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:

• step1: 创建一个BlobBuilder，它内部也会分配一些内存出来;
• step2: 使用BlobBuilder.ContructRoot 函数来构建一个root blobasset出来。
• Step3: 把数据填写到blobasset种，保存起来;
• Step4: 使用BlobBuilder.CreateBlobAssetReference来创建一个BlobAssetReference来方便读取与使用Blobasset种的数据;
• Step5: 把BlobBuilder对象释放掉。

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;
}

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:

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;
}

存储string到BlobAsset, 代码如下:

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;
}

存储BlobPtr数据到BlobAsset，代码如下:

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;
  }

这里的BlobPtr是基于数据的偏移来存储的;