From 205d4b5ff37c7b49db5c337523a657f2ebd551d6 Mon Sep 17 00:00:00 2001
From: RaveYard <29225776+MrRaveYard@users.noreply.github.com>
Date: Tue, 27 Feb 2024 03:01:37 +0100
Subject: [PATCH] Support negative fadestep for particles

---
 src/playsim/p_actionfunctions.cpp | 3 ++-
 src/playsim/p_effect.cpp          | 5 ++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/playsim/p_actionfunctions.cpp b/src/playsim/p_actionfunctions.cpp
index 4c842d3bb..76d6be9fd 100644
--- a/src/playsim/p_actionfunctions.cpp
+++ b/src/playsim/p_actionfunctions.cpp
@@ -1691,7 +1691,8 @@ DEFINE_ACTION_FUNCTION(AActor, A_SpawnParticleEx)
 	PARAM_FLOAT	(rollacc)
 
 	startalpha = clamp(startalpha, 0., 1.);
-	if (fadestep > 0) fadestep = clamp(fadestep, 0., 1.);
+	fadestep = clamp(fadestep, -1.0, 1.0);
+
 	size = fabs(size);
 	if (lifetime != 0)
 	{
diff --git a/src/playsim/p_effect.cpp b/src/playsim/p_effect.cpp
index 7b1b0a87b..5ee7e9f3c 100644
--- a/src/playsim/p_effect.cpp
+++ b/src/playsim/p_effect.cpp
@@ -306,10 +306,9 @@ void P_ThinkParticles (FLevelLocals *Level)
 			continue;
 		}
 		
-		auto oldtrans = particle->alpha;
 		particle->alpha -= particle->fadestep;
 		particle->size += particle->sizestep;
-		if (particle->alpha <= 0 || oldtrans < particle->alpha || --particle->ttl <= 0 || (particle->size <= 0))
+		if (particle->alpha <= 0 || --particle->ttl <= 0 || (particle->size <= 0))
 		{ // The particle has expired, so free it
 			*particle = {};
 			if (prev)
@@ -375,7 +374,7 @@ void P_SpawnParticle(FLevelLocals *Level, const DVector3 &pos, const DVector3 &v
 		particle->Acc = FVector3(accel);
 		particle->color = ParticleColor(color);
 		particle->alpha = float(startalpha);
-		if (fadestep < 0) particle->fadestep = FADEFROMTTL(lifetime);
+		if (fadestep <= -1.0) particle->fadestep = FADEFROMTTL(lifetime);
 		else particle->fadestep = float(fadestep);
 		particle->ttl = lifetime;
 		particle->size = size;