From 386ae2067b5e89ed41811acaa7d685d640218233 Mon Sep 17 00:00:00 2001
From: SNMetamorph <25657591+SNMetamorph@users.noreply.github.com>
Date: Fri, 7 May 2021 21:53:15 +0400
Subject: [PATCH] engine: client: another interpolation fix

---
 engine/client/cl_main.c | 47 +++++++++++++++++++++--------------------
 engine/client/client.h  |  4 ++--
 2 files changed, 26 insertions(+), 25 deletions(-)

diff --git a/engine/client/cl_main.c b/engine/client/cl_main.c
index 0e475b4d..b6ec739b 100644
--- a/engine/client/cl_main.c
+++ b/engine/client/cl_main.c
@@ -241,6 +241,11 @@ void CL_SignonReply( void )
 	}
 }
 
+float CL_LerpInterval( void )
+{
+	return max( cl_interp->value, 1.f / cl_updaterate->value );
+}
+
 /*
 ===============
 CL_LerpPoint
@@ -291,12 +296,13 @@ static float CL_LerpPoint( void )
 	if( cl_interp->value > 0.001f )
 	{
 		// manual lerp value (goldsrc mode)
-		frac = ( cl.time - cl.mtime[1] ) / cl_interp->value;
+		float td = max( 0.f, cl.time - cl.mtime[0] );
+		frac = td / CL_LerpInterval();
 	}
 	else if( server_frametime > 0.001f )
 	{
 		// automatic lerp (classic mode)
-		frac = ( cl.time - cl.mtime[1] ) / server_frametime;
+		frac = ( cl.time - cl.mtime[1] ) / server_frametime;  
 	}
 #endif
 	return frac;
@@ -339,10 +345,10 @@ Validate interpolation cvars, calc interpolation window
 */
 void CL_ComputeClientInterpolationAmount( usercmd_t *cmd )
 {
-	int	min_interp = MIN_EX_INTERP;
-	int	max_interp = MAX_EX_INTERP;
-	int	interpolation_msec;
-	qboolean	forced = false;
+	const float epsilon = 0.001f; // to avoid float invalid comparision
+	float min_interp = MIN_EX_INTERP;
+	float max_interp = MAX_EX_INTERP;
+	float interpolation_time;
 
 	if( cl_updaterate->value < MIN_UPDATERATE )
 	{
@@ -357,29 +363,24 @@ void CL_ComputeClientInterpolationAmount( usercmd_t *cmd )
 	}
 
 	if( cls.spectator )
-		max_interp = 200;
+		max_interp = 0.2f;
 
-	min_interp = 1000.0f / cl_updaterate->value;
-	min_interp = Q_max( 1, min_interp );
-	interpolation_msec = cl_interp->value * 1000.0f;
-
-	if(( interpolation_msec + 1 ) < min_interp )
+	min_interp = 1.0f / cl_updaterate->value;
+	interpolation_time = CL_LerpInterval( );
+	
+	if( (cl_interp->value + epsilon) < min_interp )
 	{
-		Con_Printf( "ex_interp forced up to %i msec\n", interpolation_msec );
-		interpolation_msec = min_interp;
-		forced = true;
+		Con_Printf( "ex_interp forced up to %.1f msec\n", min_interp * 1000.f );
+		Cvar_SetValue( "ex_interp", min_interp );
 	}
-	else if(( interpolation_msec - 1 ) > max_interp )
+	else if( (cl_interp->value - epsilon) > max_interp )
 	{
-		Con_Printf( "ex_interp forced down to %i msec\n", interpolation_msec );
-		interpolation_msec = max_interp;
-		forced = true;
+		Con_Printf( "ex_interp forced down to %.1f msec\n", max_interp * 1000.f );
+		Cvar_SetValue( "ex_interp", max_interp );
 	}
 
-	if( forced ) Cvar_SetValue( "ex_interp", (float)interpolation_msec * 0.001f );
-	interpolation_msec = bound( min_interp, interpolation_msec, max_interp );
-
-	cmd->lerp_msec = CL_DriftInterpolationAmount( interpolation_msec );
+	interpolation_time = bound( min_interp, interpolation_time, max_interp );
+	cmd->lerp_msec = CL_DriftInterpolationAmount( interpolation_time * 1000 );
 }
 
 /*
diff --git a/engine/client/client.h b/engine/client/client.h
index 4dcdd6dd..0a239d7f 100644
--- a/engine/client/client.h
+++ b/engine/client/client.h
@@ -107,8 +107,8 @@ extern int CL_UPDATE_BACKUP;
 #define MIN_UPDATERATE	10.0f
 #define MAX_UPDATERATE	102.0f
 
-#define MIN_EX_INTERP	50.0f
-#define MAX_EX_INTERP	100.0f
+#define MIN_EX_INTERP	0.005f
+#define MAX_EX_INTERP	0.1f
 
 #define CL_MIN_RESEND_TIME	1.5f		// mininum time gap (in seconds) before a subsequent connection request is sent.
 #define CL_MAX_RESEND_TIME	20.0f		// max time.  The cvar cl_resend is bounded by these.