From ae10a58aa452de51220db60a2954e4761538e5a0 Mon Sep 17 00:00:00 2001
From: wootguy <drake.rhunter@gmail.com>
Date: Tue, 19 Nov 2024 06:12:44 -0800
Subject: [PATCH] improve lag compensation

reduced rewind error (about 20ms -> 10ms average). Blood splashes don't lag behind the monster.
---
 dlls/monster/CBaseMonster.cpp |  5 ++++-
 dlls/util/lagcomp.cpp         | 37 ++++++++++++++++++++++++-----------
 dlls/util/lagcomp.h           |  3 +++
 3 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/dlls/monster/CBaseMonster.cpp b/dlls/monster/CBaseMonster.cpp
index 80338791..03ef18c1 100644
--- a/dlls/monster/CBaseMonster.cpp
+++ b/dlls/monster/CBaseMonster.cpp
@@ -14,6 +14,7 @@
 #include "defaultai.h"
 #include "CMonsterMaker.h"
 #include "hlds_hooks.h"
+#include "lagcomp.h"
 
 #define MONSTER_CUT_CORNER_DIST		8 // 8 means the monster's bounding box is contained without the box of the node in WC
 
@@ -4814,10 +4815,12 @@ void CBaseMonster::TraceAttack(entvars_t* pevAttacker, float flDamage, Vector ve
 			UTIL_Shrapnel(ptr->vecEndPos, ptr->vecPlaneNormal, flDamage, bitsDamageType);
 		}
 		if (bitsDamageType & DMG_BLOOD) {
+			Vector bloodPos = ptr->vecEndPos + get_lagcomp_offset(entindex());
+
 			// headshots should always show big blood, no matter how little damage was done.
 			// The idea is that blood size should be used primarly as an indicator that you hit the weak point.
 			float bloodSize = ptr->iHitgroup == HITGROUP_HEAD ? V_max(flDamage, 30) : flDamage;
-			SpawnBlood(ptr->vecEndPos, BloodColor(), bloodSize);
+			SpawnBlood(bloodPos, BloodColor(), bloodSize);
 			TraceBleed(bloodSize, vecDir, ptr, bitsDamageType);
 		}
 
diff --git a/dlls/util/lagcomp.cpp b/dlls/util/lagcomp.cpp
index c606d556..345c4a4b 100644
--- a/dlls/util/lagcomp.cpp
+++ b/dlls/util/lagcomp.cpp
@@ -21,7 +21,6 @@ struct WorldState {
 };
 
 struct RewindInfo {
-	bool wasRewound;
 	bool isCompensated;
 	EntState restoreState;
 };
@@ -40,6 +39,18 @@ cvar_t* sv_unlag = NULL;
 int g_pingHistoryIdx = 0;
 float g_pingHistory[PING_SMOOTHING_COUNT][32];
 
+int g_currentRewindIdx = 0;
+
+Vector get_lagcomp_offset(int entindex) {
+	RewindInfo& info = g_rewinds[entindex];
+
+	if (info.isCompensated) {
+		return info.restoreState.origin - g_worldHistory[g_currentRewindIdx].ents[entindex].origin;
+	}
+
+	return g_vecZero;
+}
+
 void update_player_pings() {
 	for (int i = 1; i <= gpGlobals->maxClients; i++) {
 		CBaseEntity* plr = UTIL_PlayerByIndex(i);
@@ -137,18 +148,22 @@ void lagcomp_begin(CBasePlayer* plr) {
 	bool foundState = false;
 	float now = g_engfuncs.pfnTime();
 	float targetTime = now - ping;
+	float bestDelta = FLT_MAX;
 
 	for (int i = 0; i < g_historyWritten; i++) {
+		float delta = fabs(g_worldHistory[i].time - targetTime);
 
-		if (g_worldHistory[idx].time <= targetTime) {
+		if (delta < bestDelta) {
+			bestDelta = delta;
 			foundState = true;
-			break;
-		}
-		else if (--idx < 0) {
-			idx = MAX_UNLAG_STATES - 1;
+			idx = i;
 		}
 	}
 
+	g_currentRewindIdx = idx;
+
+	//ALERT(at_console, "best delta %.3f, comp %.2f ago\n", bestDelta, now - targetTime);
+
 	if (!foundState) {
 		ALERT(at_console, "Can't rewind for %.2fs ping.\n", ping);
 		return;
@@ -177,11 +192,11 @@ void lagcomp_begin(CBasePlayer* plr) {
 		restoreState.sequence = vars.sequence;
 		restoreState.frame = vars.frame;
 
-		EntState& entState = worldState.ents[i];
-		vars.sequence = entState.sequence;
-		vars.frame = entState.frame;
-		vars.angles = entState.angles;
-		UTIL_SetOrigin(&vars, entState.origin);
+		EntState& rewindState = worldState.ents[i];
+		vars.sequence = rewindState.sequence;
+		vars.frame = rewindState.frame;
+		vars.angles = rewindState.angles;
+		UTIL_SetOrigin(&vars, rewindState.origin);
 	}
 
 	g_didRewind = true;
diff --git a/dlls/util/lagcomp.h b/dlls/util/lagcomp.h
index 3d6b821f..9186812e 100644
--- a/dlls/util/lagcomp.h
+++ b/dlls/util/lagcomp.h
@@ -10,3 +10,6 @@ void lagcomp_begin(CBasePlayer* plr);
 
 // must be called after lagcomp_begin to restore the current world state after a rewind
 void lagcomp_end();
+
+// returns difference between lag compensated position and server's position
+Vector get_lagcomp_offset(int entindex);
\ No newline at end of file