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如何获取客户端上可玩性属性的delta值(属性值更改后)?

unreal-gameplay-ability-system unreal-engine4 c++

Richard · 技术社区 · 6 年前

在我的虚幻引擎项目中,它使用 GameplayAbilitySystem 默认的服务器->客户机体系结构会通知客户机服务器上发生的属性值更改。

另外,我不仅要得到新值,还要得到值的变化量( delta = new value - old value )。这应该可以使用 attribute value change delegate ,因为它包含 FOnAttributeChangeData 和它的成员 NewValue 和 OldValue .

在服务器上,两个值都是正确的。然而,在客户身上, FOnAttributeChangeData::NewValue == FOnAttributeChangeData::OldValue 两者的价值相同 新值 在服务器上。

这是因为委托被调用之后复制已发生…

UPROPERTY(ReplicatedUsing=OnRep_MyAttribute)
FGameplayAttributeData MyAttribute;

void UAttributeSetBase::OnRep_MyAttribute()
{
    GAMEPLAYATTRIBUTE_REPNOTIFY(UAttributeSetBase, MyAttribute);
}

(这是的默认气体设置 ActionRPG )

…所以客户机不知道它在复制之前的价值。

如何获取属性的值,该属性在被服务器更新之前已具有该值?
如何将此值转发给代理?

1 回复 | 直到 6 年前

Richard 6 年前

获取旧值(问题1)

unrealengine onrep函数将复制变量的前一个状态作为 OnRep 功能。所以添加参数

void UAttributeSetBase::OnRep_MyAttribute(const FGameplayAttributeData& Previous)
{
    const auto PreviousValue = Previous.GetCurrentValue(); // See below for possible usage.
    GAMEPLAYATTRIBUTE_REPNOTIFY(UAttributeSetBase, MyAttribute);
}

感谢来自虚幻气体不和谐频道的@dan。

将值转发给代表(问题2)

想法

当您的目标是不修改ue4源代码时,一种可能是在属性集中缓存上一个值,这样您就可以从外部访问它。

为属性集中的每个属性缓存该值 OnReP 功能。
使用委托中的缓存值,但是 只有当它是有效的 . 因为该值是在 OnReP 函数,它将不存在于服务器上。这非常好,因为我们希望保留服务器上的行为,它使用 FOnAttributeChangeData::OldValue (只有在服务器上才有正确的值)。

示例实现

缓存上一个值

属性数据库.h:

// Wrapper for a TMap. If you need thread safety, use another container or allocator.
class CachePreviousDataFromReplication
{
    TMap<FName, FGameplayAttributeData> CachedPreviousData;
public:
    void Add(const FName, const FGameplayAttributeData&);
    auto Find(const FName) const -> const FGameplayAttributeData*;
};
class YOUR_API UAttributeSetBase : public UAttributeSet
{
    // ...
private:
    UFUNCTION() void OnRep_MyAttribute(const FGameplayAttributeData& Previous);
    // ...
private:
    CachePreviousDataFromReplication CachedDataFromReplication;
public:
    // \param[in]   AttributeName   Use GET_MEMBER_NAME_CHECKED() to retrieve the name.
    auto GetPreviousDataFromReplication(const FName AttributeName) const -> const FGameplayAttributeData*;
}

属性数据库.cpp:

void CachePreviousDataFromReplication::Add(const FName AttributeName, const FGameplayAttributeData& AttributeData)
{
    this->CachedPreviousData.Add(AttributeName, AttributeData);
}

auto CachePreviousDataFromReplication::Find(const FName AttributeName) const -> const FGameplayAttributeData*
{
    return CachedPreviousData.Find(AttributeName);
}

void UAttributeSetBase::OnRep_MyAttribute(const FGameplayAttributeData& Previous)
{
    CachedDataFromReplication.Add(GET_MEMBER_NAME_CHECKED(UAttributeSetBase, MyAttribute), Previous); // Add this to every OnRep function.
    GAMEPLAYATTRIBUTE_REPNOTIFY(UAttributeSetBase, MyAttribute);
}

auto UAttributeSetBase::GetPreviousDataFromReplication(const FName AttributeName) const -> const FGameplayAttributeData*
{
    return CachedDataFromReplication.Find(AttributeName);
}

访问委托中的上一个值

无杆菌碱.h:

class YOUR_API ACharacterBase : public ACharacter, public IAbilitySystemInterface
{
    // ...
    void OnMyAttributeValueChange(const FOnAttributeChangeData& Data); // The callback to be registered within GAS.
    // ...
}

AcharacterBase.cpp:

void ACharacterBase::OnMyAttributeValueChange(const FOnAttributeChangeData& Data)
{
    // This delegate is fired either from
    // 1. `SetBaseAttributeValueFromReplication` or from
    // 2. `InternalUpdateNumericalAttribute`
    // #1 is called on clients, after the attribute has changed its value. This implies,
    // that the previous value is not present on the client anymore. Therefore, the
    // value of `Data.OldValue` is erroneously identical to `Data.NewValue`.
    // In that case (and only in that case), the previous value is retrieved from a cache
    // in the AttributeSet. This cache will be only present on client, after it had
    // received an update from replication.
    auto deltaValue = 0.f;
    if (Data.NewValue == Data.OldValue)
    {
        const auto attributeName = GET_MEMBER_NAME_CHECKED(UAttributeSetBase, MyAttribute);
        if (auto previousData = AttributeSetComponent->GetPreviousDataFromReplication(attributeName))
        {
            // This will be called on the client, when coming from replication.
            deltaValue = Data.NewValue - previousData->GetCurrentValue();
        }
    }
    else
    {
        // This might be called on the server or clients, when coming from
        // `InternalUpdateNumericalAttribute`.
        deltaValue = Data.NewValue - Data.OldValue;
    }
    // Use deltaValue as you like.
}