fix clients freezing in areas with lots of entities

when a client enters a new area with 200+ ents, it freezes with message "datagram overflowed" spammed in the server console. Sometimes the client eventually receives all the data, but not always.

Another source of freezing comes from MAX_PHYSENTS. If near the limit, the player will become completely stuck. Not even noclip can save them.

This change limits the amount of new entities per frame so that players gradually receive the full state. Some entities will be invisible while catching up, which is less than a second at cl_updaterate 10, and almost instant at the default 60. MAX_PHYSENTS was also increased from 600 -> 2048. A rehlds update is required or else the server crashes instantly.

MAX_PACKET_ENTITIES was lowered to a practical limit. The client can't actually handle 1024, it's more like 500.

dlls/hooks/hlds_hooks.cpp

@@ -1112,6 +1112,7 @@ void SpectatorThink( edict_t *pEntity )
 
 int g_numEdictOverflows[32];
 int g_numPacketEntities[32];
+int g_newPacketEnts;
 
 /*
 ================
@@ -1170,6 +1171,7 @@ void SetupVisibility( edict_t *pViewEntity, edict_t *pClient, unsigned char **pv
 
 	g_numEdictOverflows[g_packClientIdx] = 0;
 	g_numPacketEntities[g_packClientIdx] = 0;
+	g_newPacketEnts = 0;	
 }
 
 #include "entity_state.h"
@@ -1196,6 +1198,7 @@ int AddToFullPack( struct entity_state_s *state, int e, edict_t *ent, edict_t *h
 		return 0; // should never happen?
 
 	uint32_t plrbit = PLRBIT(host);
+	bool isNewlyVisible = !(baseent->m_netPlayers & plrbit);
 	baseent->m_pvsPlayers &= ~plrbit;
 	baseent->m_pasPlayers &= ~plrbit;
 	baseent->m_netPlayers &= ~plrbit;
@@ -1385,12 +1388,20 @@ int AddToFullPack( struct entity_state_s *state, int e, edict_t *ent, edict_t *h
 			// TODO: fix this in a client mod
 			state->angles.x = ent->v.v_angle.x;
 		}
-
+	}
+
+	if (baseent->Classify() != CLASS_NONE && baseent->Classify() != CLASS_MACHINE)
+		state->eflags |= EFLAG_FLESH_SOUND;
+	else
+		state->eflags &= ~EFLAG_FLESH_SOUND;
+
+	if (!baseent->AddToFullPack(state, plr)) {
+		return 0;
 	}
 
 	client_info_t client = plr->GetClientInfo();
 	if (e >= client.max_edicts) {
-		ALERT(at_console, "Can't send edict %d '%s' (index too high)\n", e, STRING(ent->v.classname));
+		//ALERT(at_console, "Can't send edict %d '%s' (index too high)\n", e, STRING(ent->v.classname));
 		g_numEdictOverflows[g_packClientIdx]++;
 		plr->SendLegacyClientWarning();
 		return 0;
@@ -1401,26 +1412,26 @@ int AddToFullPack( struct entity_state_s *state, int e, edict_t *ent, edict_t *h
 		plr->SendLegacyClientWarning();
 		return 0;
 	}
-	if (g_numPacketEntities[g_packClientIdx] + 1 >= client.max_packet_entities) {
-		ALERT(at_console, "Can't send edict %d '%s' (exceeded %d MAX_PACKET_ENTITIES)\n",
-			e, STRING(ent->v.classname), client.max_packet_entities);
+	if (g_numPacketEntities[g_packClientIdx] >= client.max_packet_entities) {
+		//ALERT(at_console, "Can't send edict %d '%s' (exceeded %d MAX_PACKET_ENTITIES)\n",
+		//	e, STRING(ent->v.classname), client.max_packet_entities);
 		g_numEdictOverflows[g_packClientIdx]++;
 		plr->SendLegacyClientWarning();
 		return 0;
 	}
 
-	if (baseent->Classify() != CLASS_NONE && baseent->Classify() != CLASS_MACHINE)
-		state->eflags |= EFLAG_FLESH_SOUND;
-	else
-		state->eflags &= ~EFLAG_FLESH_SOUND;
+	if (isNewlyVisible) {
+		if (g_newPacketEnts > MAX_NEW_PACKET_ENTITIES) {
+			// don't send too many new entities at once or else the client freezes with "datagram overflow"
+			return 0;
+		}
+
+		g_newPacketEnts++;
+	}
 
 	baseent->m_netPlayers |= plrbit;
 	g_numPacketEntities[g_packClientIdx]++;
 
-	if (!baseent->AddToFullPack(state, plr)) {
-		return 0;
-	}
-
 	return 1;
 }
 

dlls/player/CBasePlayer.h

@@ -90,9 +90,20 @@ enum sbar_data
 #define MAX_CLIENT_ENTS 1665 // default for the latest HL client from steam
 #define MAX_LEGACY_CLIENT_ENTS 1365 // default when using the steam_legacy beta
 
-#define MAX_PACKET_ENTITIES 1024
+// This was increased to 1024 for HL25 but client limits make most of those new slots useless.
+// Sending more than ~800 crashes the client
+// Sending more than 512 makes temporary effects disappear (explosions)
+// Sending more than 500 makes temporary effects flicker and sometimes disappear
+#define MAX_PACKET_ENTITIES 500
+
+// unlike HL25, temporary effects don't start disappearing near the packet entity limit
 #define MAX_LEGACY_PACKET_ENTITIES 256
 
+// max number of new entities per packet
+// more than ~128 new ents ar once makes clients freeze with "datagram overflow" which is not
+// always recoverable. 64 fills up MAX_PACKET_ENTITIES very fast even at cl_updaterate 10
+#define MAX_NEW_PACKET_ENTITIES 64
+
 enum HL_CLIENT_ENGINE_VERSION {
 	CLIENT_ENGINE_NOT_CHECKED,	// player hasn't responded to cvar queries yet
 	CLIENT_ENGINE_HL_LATEST,	// the latest version of the steam HL client from steam

pm_shared/pm_defs.h

@@ -18,7 +18,13 @@
 #pragma once
 
 #include "archtypes.h"     // DAL
-#define	MAX_PHYSENTS 600 		  // Must have room for all entities in the world.
+
+#ifdef CLIENT_DLL
+#define	MAX_PHYSENTS 600  // Must have room for all entities in the world. Must match client engine or else instacrash.
+#else
+#define	MAX_PHYSENTS 2048 // Must match rehlds or else the server crashes instantly.
+#endif
+
 #define MAX_MOVEENTS 64
 #define	MAX_CLIP_PLANES	5