From ba77b97aaa1ced0063126cda442912c02ab70235 Mon Sep 17 00:00:00 2001
From: James R <justsomejames2@gmail.com>
Date: Sat, 12 Aug 2023 15:34:51 -0700
Subject: [PATCH] K_SpawnKartMissile: try to step down for stairs

---
 src/k_kart.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/k_kart.c b/src/k_kart.c
index 76b508a51..51ef244de 100644
--- a/src/k_kart.c
+++ b/src/k_kart.c
@@ -4768,14 +4768,15 @@ static mobj_t *K_SpawnKartMissile(mobj_t *source, mobjtype_t type, angle_t an, I
 	th->momy = FixedMul(finalspeed, FINESINE(an>>ANGLETOFINESHIFT));
 	th->momz = source->momz;
 
-	P_CheckPosition(th, x, y, NULL);
+	// Get floorz and ceilingz
+	P_SetOrigin(th, x, y, z);
 
 	if (P_MobjWasRemoved(th))
 		return NULL;
 
 	if ((P_IsObjectFlipped(th)
-			? tm.ceilingz - source->ceilingz
-			: tm.floorz - source->floorz) > P_GetThingStepUp(th, x, y))
+			? th->ceilingz - source->ceilingz
+			: th->floorz - source->floorz) > P_GetThingStepUp(th, x, y))
 	{
 		// Assuming this is on the boundary of a sector and
 		// the wall is too tall... I'm not bothering with
@@ -4795,6 +4796,26 @@ static mobj_t *K_SpawnKartMissile(mobj_t *source, mobjtype_t type, angle_t an, I
 			return NULL;
 	}
 
+	if (P_IsObjectOnGround(source))
+	{
+		// If the player is on the ground, make sure the
+		// missile spawns on the ground, so it smoothly
+		// travels down stairs.
+
+		// FIXME: This needs a more elegant solution because
+		// if multiple stairs are crossed, the height
+		// difference in the end is too great (this affects
+		// slopes too).
+
+		const fixed_t tz = P_IsObjectFlipped(th) ? th->ceilingz - th->height : th->floorz;
+
+		if (abs(tz - z) <= P_GetThingStepUp(th, x, y))
+		{
+			z = tz;
+			th->z = z;
+		}
+	}
+
 	if (source->player != NULL)
 	{
 		th->cusval = source->player->itemscale;