NPC Lag Compensation

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如果没有延迟补偿(en)，当您射击目标时，必须考虑您的网络延迟时间并相应地向前瞄准。例如，如果您的延迟是100毫秒，您必须瞄准目标头部在100毫秒后的位置，而不是当前看到的位置。

显然这并不理想，因此多人Source游戏实现了延迟补偿。在计算子弹是否命中时，会暂时将所有玩家的位置回退到射击者的延迟时间，从而根据射击者开火时看到的精确画面进行碰撞计算。该效果在NPC中缺失，但可以通过复制玩家延迟补偿代码来实现。

本教程详细说明了所有需要的修改——虽然涉及大量代码，但其中95%是从玩家延迟补偿代码中复制的。

ai_basenpc.h

在此行之前：

typedef CBitVec<MAX_CONDITIONS> CAI_ScheduleBits;

添加以下代码（取自player_lagcompensation.cpp但已修改）：

#define MAX_LAYER_RECORDS (CBaseAnimatingOverlay::MAX_OVERLAYS)

struct LayerRecordNPC
{
	int m_sequence;
	float m_cycle;
	float m_weight;
	int m_order;

	LayerRecordNPC()
	{
		m_sequence = 0;
		m_cycle = 0;
		m_weight = 0;
		m_order = 0;
	}

	LayerRecordNPC( const LayerRecordNPC& src )
	{
		m_sequence = src.m_sequence;
		m_cycle = src.m_cycle;
		m_weight = src.m_weight;
		m_order = src.m_order;
	}
};

struct LagRecordNPC
{
public:
	LagRecordNPC()
	{
		m_fFlags = 0;
		m_vecOrigin.Init();
		m_vecAngles.Init();
		m_vecMins.Init();
		m_vecMaxs.Init();
		m_flSimulationTime = -1;
		m_masterSequence = 0;
		m_masterCycle = 0;
	}

	LagRecordNPC( const LagRecordNPC& src )
	{
		m_fFlags = src.m_fFlags;
		m_vecOrigin = src.m_vecOrigin;
		m_vecAngles = src.m_vecAngles;
		m_vecMins = src.m_vecMins;
		m_vecMaxs = src.m_vecMaxs;
		m_flSimulationTime = src.m_flSimulationTime;
		for( int layerIndex = 0; layerIndex < MAX_LAYER_RECORDS; ++layerIndex )
		{
			m_layerRecords[layerIndex] = src.m_layerRecords[layerIndex];
		}
		m_masterSequence = src.m_masterSequence;
		m_masterCycle = src.m_masterCycle;
	}

	// 玩家是否在本帧死亡
	int						m_fFlags;

	// 玩家位置、朝向和包围盒
	Vector					m_vecOrigin;
	QAngle					m_vecAngles;
	Vector					m_vecMins;
	Vector					m_vecMaxs;

	float					m_flSimulationTime;	
	
	// 玩家动画细节，用于正确计算腿部位置
	LayerRecordNPC			m_layerRecords[MAX_LAYER_RECORDS];
	int						m_masterSequence;
	float					m_masterCycle;
};

我们将NPC的延迟记录直接附加到NPC上以避免混淆，因此NPC代码需要能访问这些记录。

在CAI_BaseNPC类定义中添加：

public:
	CUtlFixedLinkedList<LagRecordNPC>* GetLagTrack() { return m_LagTrack; }
	LagRecordNPC*	GetLagRestoreData() { if ( m_RestoreData != NULL ) return m_RestoreData; else return new LagRecordNPC(); }
	LagRecordNPC*	GetLagChangeData() { if ( m_ChangeData != NULL ) return m_ChangeData; else return new LagRecordNPC(); }
	void		SetLagRestoreData(LagRecordNPC* l) { if ( m_RestoreData != NULL ) delete m_RestoreData; m_RestoreData = l; }
	void		SetLagChangeData(LagRecordNPC* l) { if ( m_ChangeData != NULL ) delete m_ChangeData; m_ChangeData = l; }
	void		FlagForLagCompensation( bool tempValue ) { m_bFlaggedForLagCompensation = tempValue; }
	bool		IsLagFlagged() { return m_bFlaggedForLagCompensation; }

private:
	CUtlFixedLinkedList<LagRecordNPC>* m_LagTrack;
	LagRecordNPC*	m_RestoreData;
	LagRecordNPC*	m_ChangeData;
	bool		m_bFlaggedForLagCompensation;

这个"延迟记录"存储NPC的历史位置和动画信息。

ai_basenpc.cpp

在CAI_BaseNPC构造函数末尾添加：

m_LagTrack = new CUtlFixedLinkedList< LagRecordNPC >();

在析构函数开头添加：

m_LagTrack->Purge();
delete m_LagTrack;

player.cpp/player.h

将函数WantsLagCompensationOnEntity的第一个参数从const CBasePlayer *pPlayer改为const CBaseEntity *pEntity。

在函数中将所有pPlayer引用改为pEntity，并替换以下行：

float maxDistance = 1.5 * pPlayer->MaxSpeed() * sv_maxunlag.GetFloat();

改为：

float maxspeed;
CBasePlayer *pPlayer = ToBasePlayer((CBaseEntity*)pEntity);
if ( pPlayer )
	maxspeed = pPlayer->MaxSpeed();
else
	maxspeed = 600;
float maxDistance = 1.5 * maxspeed * sv_maxunlag.GetFloat();

hl2mp_player.cpp/hl2mp_player.h

修改CHL2MP_Player::WantsLagCompensationOnEntity函数：

bool CHL2MP_Player::WantsLagCompensationOnEntity( const CBaseEntity *pEntity, const CUserCmd *pCmd, const CBitVec<MAX_EDICTS> *pEntityTransmitBits ) const
{
	if ( !( pCmd->buttons & IN_ATTACK ) && (pCmd->command_number - m_iLastWeaponFireUsercmd > 5) )
		return false;

	return BaseClass::WantsLagCompensationOnEntity(pEntity,pCmd,pEntityTransmitBits);
}

player_lagcompensation.cpp

添加头文件：

#include "ai_basenpc.h"

添加NPC回溯函数：

static void RestoreEntityTo( CAI_BaseNPC *pEntity, const Vector &vWantedPos )
{
	// 尝试从当前位置移动到目标位置
	trace_t tr;
	UTIL_TraceEntity( pEntity, vWantedPos, vWantedPos, MASK_NPCSOLID, pEntity, COLLISION_GROUP_NPC, &tr );
	if ( tr.startsolid || tr.allsolid )
	{
		// 回溯失败处理...
	}
	else
	{
		UTIL_SetOrigin( pEntity, tr.endpos, true );
	}
}

在CLagCompensationManager类中添加：

void BacktrackEntity( CAI_BaseNPC *entity, float flTargetTime );

更新FrameUpdatePostEntityThink函数，添加NPC处理循环。

修改StartLagCompensation函数，添加NPC标记初始化。

在碰撞检测部分添加NPC处理分支。

实现BacktrackEntity函数，完整复制玩家回溯逻辑并适配NPC。

最后在FinishLagCompensation中添加NPC状态恢复代码。

验证方法

在控制台输入： sv_cheats 1 sv_showlagcompensation 1 射击NPC时会出现蓝色骨骼框表示延迟补偿生效。