From d0a4310bade4d1f65f9b8ac59bc0d1178d6f17fe Mon Sep 17 00:00:00 2001
From: serge_shubin <serge@generalarcade.com>
Date: Tue, 24 Mar 2026 19:38:22 +0800
Subject: [PATCH] Add svdemo_seekexact for precise seeking with read-forward
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svdemo_seek snaps to the nearest keyframe (fast, ±interval accuracy).
svdemo_seekexact reads forward from the keyframe to the exact target
time, giving frame-accurate positioning at the cost of a brief
processing delay.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 code/server/server.h     |  1 +
 code/server/sv_ccmds.c   |  1 +
 code/server/sv_netdemo.c | 70 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

diff --git a/code/server/server.h b/code/server/server.h
index ec44870..6d59686 100644
--- a/code/server/server.h
+++ b/code/server/server.h
@@ -356,6 +356,7 @@ void		SVD_CleanupPlayback( void );
 void		SVD_Stop_f( void );
 void		SVD_Pause_f( void );
 void		SVD_Seek_f( void );
+void		SVD_SeekExact_f( void );
 qboolean	SVD_PlaybackFrame( void );
 qboolean	SVD_IsRecording( void );
 qboolean	SVD_IsPlaying( void );
diff --git a/code/server/sv_ccmds.c b/code/server/sv_ccmds.c
index 3e4df9b..7f1370f 100644
--- a/code/server/sv_ccmds.c
+++ b/code/server/sv_ccmds.c
@@ -746,6 +746,7 @@ void SV_AddOperatorCommands( void ) {
 	Cmd_AddCommand ("svdemo_play", SVD_Play_f);
 	Cmd_AddCommand ("svdemo_pause", SVD_Pause_f);
 	Cmd_AddCommand ("svdemo_seek", SVD_Seek_f);
+	Cmd_AddCommand ("svdemo_seekexact", SVD_SeekExact_f);
 }
 
 /*
diff --git a/code/server/sv_netdemo.c b/code/server/sv_netdemo.c
index 3409341..f443f05 100644
--- a/code/server/sv_netdemo.c
+++ b/code/server/sv_netdemo.c
@@ -1104,6 +1104,76 @@ void SVD_Seek_f( void ) {
 	Com_Printf( "Seeked to time %d.\n", svs.time );
 }
 
+void SVD_SeekExact_f( void ) {
+	int targetTime, i, bestKf;
+	float seconds;
+
+	if ( !demo.playing ) {
+		Com_Printf( "Not playing a server demo.\n" );
+		return;
+	}
+
+	if ( Cmd_Argc() < 2 ) {
+		Com_Printf( "Usage: svdemo_seekexact <seconds>\n" );
+		return;
+	}
+
+	if ( demo.numKeyframes <= 0 ) {
+		Com_Printf( "No keyframes in this demo.\n" );
+		return;
+	}
+
+	seconds = atof( Cmd_Argv(1) );
+	targetTime = svs.time + (int)(seconds * 1000);
+
+	// find nearest keyframe at or before target time
+	bestKf = -1;
+	for ( i = 0; i < demo.numKeyframes; i++ ) {
+		if ( demo.keyframeTimes[i] <= targetTime ) {
+			bestKf = i;
+		} else {
+			break;
+		}
+	}
+
+	if ( bestKf < 0 ) {
+		bestKf = 0;
+		targetTime = demo.keyframeTimes[0];
+	}
+
+	// seek to keyframe
+	FS_Seek( demo.playFile, demo.keyframeOffsets[bestKf], FS_SEEK_SET );
+	Com_Memset( demo.playPrevEntities, 0, sizeof(demo.playPrevEntities) );
+	Com_Memset( demo.playPrevPlayers, 0, sizeof(demo.playPrevPlayers) );
+	svs.time = demo.keyframeTimes[bestKf];
+	svs.snapFlagServerBit ^= SNAPFLAG_SERVERCOUNT;
+	demo.seeked = qtrue;
+	demo.endOfDemo = qfalse;
+
+	// read forward from keyframe to target time
+	while ( svs.time < targetTime ) {
+		if ( !SVD_ReadFrame( demo.playFile ) ) {
+			demo.endOfDemo = qtrue;
+			break;
+		}
+	}
+
+	// reset client snapshot timing
+	{
+		int j;
+		for ( j = 0; j < sv_maxclients->integer; j++ ) {
+			if ( svs.clients[j].state >= CS_ACTIVE ) {
+				svs.clients[j].nextSnapshotTime = svs.time;
+			}
+		}
+	}
+
+	sv.timeResidual = 1000 / sv_fps->integer;
+
+	Com_Printf( "Seeked to time %d (read forward %d ms from keyframe).\n",
+		svs.time, svs.time - demo.keyframeTimes[bestKf] );
+}
+
 /*
 Called from SV_Frame() to advance playback by one frame.
 Returns qtrue if a frame was read, qfalse if demo ended.