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Unity DOTS系列之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。
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来给用户操作数据。参考代码如下:
struct MarketData
{
public float PriceOranges;
public float PriceApples;
}
BlobAssetReference 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();
// 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(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 Hobbies;
}
BlobAssetReference CreateHobbyPool()
{
var builder = new BlobBuilder(Allocator.Temp);
ref HobbyPool hobbyPool = ref builder.ConstructRoot();
// Allocate enough room for two hobbies in the pool. Use the returned BlobBuilderArray
// to fill in the data.
const int numHobbies = 2;
BlobBuilderArray 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(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 CreateCharacterSetup(string name)
{
var builder = new BlobBuilder(Allocator.Temp);
ref CharacterSetup character = ref builder.ConstructRoot();
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(Allocator.Persistent);
builder.Dispose();
return result;
}
#endregion
存储BlobPtr数据到BlobAsset，代码如下:
#region CreateBlobAssetWithInternalPointer
struct FriendList
{
public BlobPtr BestFriend;
public BlobArray Friends;
}
BlobAssetReference CreateFriendList()
{
var builder = new BlobBuilder(Allocator.Temp);
ref FriendList friendList = ref builder.ConstructRoot();
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(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,持续更新！
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