From 1affc36f0628ffb380428b26303ff534aa735204 Mon Sep 17 00:00:00 2001
From: Alibek Omarov <a1ba.omarov@gmail.com>
Date: Tue, 18 Apr 2023 17:28:20 +0300
Subject: [PATCH] engine: client: more accurate ScreenShake implementation,
 thanks @vasiavasiavasia95 for sharing it

---
 engine/client/cl_game.c  | 77 +++++++++++++++++++---------------------
 engine/client/cl_parse.c | 15 +++++---
 2 files changed, 48 insertions(+), 44 deletions(-)

diff --git a/engine/client/cl_game.c b/engine/client/cl_game.c
index 43b2e952..41b32711 100644
--- a/engine/client/cl_game.c
+++ b/engine/client/cl_game.c
@@ -2119,58 +2119,52 @@ pfnCalcShake
 */
 void GAME_EXPORT pfnCalcShake( void )
 {
-	int	i;
-	float	fraction, freq;
-	float	localAmp;
-
-	if( clgame.shake.time == 0 )
-		return;
+	screen_shake_t *const shake = &clgame.shake;
+	float frametime, fraction, freq;
+	int i;
 
-	if(( cl.time > clgame.shake.time ) || clgame.shake.amplitude <= 0 || clgame.shake.frequency <= 0 )
+	if( cl.time > shake->time || shake->amplitude <= 0 || shake->frequency <= 0 || shake->duration <= 0 )
 	{
-		memset( &clgame.shake, 0, sizeof( clgame.shake ));
+		// reset shake
+		if( shake->time != 0 )
+		{
+			shake->time = 0;
+			shake->applied_angle = 0;
+			VectorClear( shake->applied_offset );
+		}
+
 		return;
 	}
 
-	if( cl.time > clgame.shake.next_shake )
+	frametime = cl_clientframetime();
+
+	if( cl.time > shake->next_shake )
 	{
-		// higher frequency means we recalc the extents more often and perturb the display again
-		clgame.shake.next_shake = cl.time + ( 1.0f / clgame.shake.frequency );
+		// get next shake time based on frequency over duration
+		shake->next_shake = (float)cl.time + shake->frequency / shake->duration;
 
-		// compute random shake extents (the shake will settle down from this)
+		// randomize each shake
 		for( i = 0; i < 3; i++ )
-			clgame.shake.offset[i] = COM_RandomFloat( -clgame.shake.amplitude, clgame.shake.amplitude );
-		clgame.shake.angle = COM_RandomFloat( -clgame.shake.amplitude * 0.25f, clgame.shake.amplitude * 0.25f );
+			shake->offset[i] = COM_RandomFloat( -shake->amplitude, shake->amplitude );
+		shake->angle = COM_RandomFloat( -shake->amplitude * 0.25f, shake->amplitude * 0.25f );
 	}
 
-	// ramp down amplitude over duration (fraction goes from 1 to 0 linearly with slope 1/duration)
-	fraction = ( clgame.shake.time - cl.time ) / clgame.shake.duration;
+	// get initial fraction and frequency values over the duration
+	fraction = ((float)cl.time - shake->time ) / shake->duration;
+	freq = fraction != 0.0f ? ( shake->frequency / fraction ) * shake->frequency : 0.0f;
 
-	// ramp up frequency over duration
-	if( fraction )
-	{
-		freq = ( clgame.shake.frequency / fraction );
-	}
-	else
-	{
-		freq = 0;
-	}
-
-	// square fraction to approach zero more quickly
-	fraction *= fraction;
+	// quickly approach zero but apply time over sine wave
+	fraction *= fraction * sin( cl.time * freq );
 
-	// Sine wave that slowly settles to zero
-	fraction = fraction * sin( cl.time * freq );
+	// apply shake offset
+	for( i = 0; i < 3; i++ )
+		shake->applied_offset[i] = shake->offset[i] * fraction;
 
-	// add to view origin
-	VectorScale( clgame.shake.offset, fraction, clgame.shake.applied_offset );
+	// apply roll angle
+	shake->applied_angle = shake->angle * fraction;
 
-	// add to roll
-	clgame.shake.applied_angle = clgame.shake.angle * fraction;
-
-	// drop amplitude a bit, less for higher frequency shakes
-	localAmp = clgame.shake.amplitude * ( host.frametime / ( clgame.shake.duration * clgame.shake.frequency ));
-	clgame.shake.amplitude -= localAmp;
+	// decrease amplitude, but slower on longer shakes or higher frequency
+	shake->amplitude -= shake->amplitude * ( frametime / ( shake->frequency * shake->duration ));
 }
 
 /*
@@ -2181,8 +2175,11 @@ pfnApplyShake
 */
 void GAME_EXPORT pfnApplyShake( float *origin, float *angles, float factor )
 {
-	if( origin ) VectorMA( origin, factor, clgame.shake.applied_offset, origin );
-	if( angles ) angles[ROLL] += clgame.shake.applied_angle * factor;
+	if( origin )
+		VectorMA( origin, factor, clgame.shake.applied_offset, origin );
+
+	if( angles )
+		angles[ROLL] += clgame.shake.applied_angle * factor;
 }
 
 /*
diff --git a/engine/client/cl_parse.c b/engine/client/cl_parse.c
index fd689ff0..8b6dbd3f 100644
--- a/engine/client/cl_parse.c
+++ b/engine/client/cl_parse.c
@@ -1854,10 +1854,17 @@ Set screen shake
 */
 void CL_ParseScreenShake( sizebuf_t *msg )
 {
-	clgame.shake.amplitude = (float)(word)MSG_ReadShort( msg ) * (1.0f / (float)(1<<12));
-	clgame.shake.duration = (float)(word)MSG_ReadShort( msg ) * (1.0f / (float)(1<<12));
-	clgame.shake.frequency = (float)(word)MSG_ReadShort( msg ) * (1.0f / (float)(1<<8));
-	clgame.shake.time = cl.time + Q_max( clgame.shake.duration, 0.01f );
+	float amplitude = (float)(word)MSG_ReadShort( msg ) * ( 1.0f / (float)( 1 << 12 ));
+	float duration  = (float)(word)MSG_ReadShort( msg ) * ( 1.0f / (float)( 1 << 12 ));
+	float frequency = (float)(word)MSG_ReadShort( msg ) * ( 1.0f / (float)( 1 << 8 ));
+
+	// don't overwrite larger existing shake
+	if( amplitude > clgame.shake.amplitude )
+		clgame.shake.amplitude = amplitude;
+
+	clgame.shake.duration = duration;
+	clgame.shake.time = cl.time + clgame.shake.duration;
+	clgame.shake.frequency = frequency;
 	clgame.shake.next_shake = 0.0f; // apply immediately
 }