From 0b5e4195936776364a247bfcef323bf9290cbdfc Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <c.oelckers@zdoom.fake>
Date: Sat, 9 Jan 2016 10:11:20 +0100
Subject: [PATCH] - fixed friction logic for sectors.

Issues with the old code:
* when calculating friction for a 3D-floor - swimmable or not - the 3D floor's top texture must be used. The previous version always checked the sector's floor texture, even though the top might as well come from the sector's ceiling.
* 3D floors never checked for the SECF_FRICTION flag at all. According to Boom specs, sector-based friction must be ignored if this is the case.
* Terrain based friction had a higher priority than the sector's own value.

Changed the rules as follows:
* if the sector's SECF_FRICTION flag is set (i.e. something explicitly changed the sector's friction), this value is used regardless of terrain settings.
* if this flag is not set, the terrain's friction is used, if defined, using the proper plane for 3D-floors.
* otherwise the default is used.
---
 src/p_map.cpp | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/p_map.cpp b/src/p_map.cpp
index f409dafa4..fe5959df9 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -529,16 +529,18 @@ void P_PlayerStartStomp(AActor *actor)
 //
 //==========================================================================
 
-inline fixed_t secfriction(const sector_t *sec)
+inline fixed_t secfriction(const sector_t *sec, int plane = sector_t::floor)
 {
-	fixed_t friction = Terrains[TerrainTypes[sec->GetTexture(sector_t::floor)]].Friction;
-	return friction != 0 ? friction : sec->friction;
+	if (sec->Flags & SECF_FRICTION) return sec->friction;
+	fixed_t friction = Terrains[TerrainTypes[sec->GetTexture(plane)]].Friction;
+	return friction != 0 ? friction : ORIG_FRICTION;
 }
 
-inline fixed_t secmovefac(const sector_t *sec)
+inline fixed_t secmovefac(const sector_t *sec, int plane = sector_t::floor)
 {
-	fixed_t movefactor = Terrains[TerrainTypes[sec->GetTexture(sector_t::floor)]].MoveFactor;
-	return movefactor != 0 ? movefactor : sec->movefactor;
+	if (sec->Flags & SECF_FRICTION) return sec->friction;
+	fixed_t movefactor = Terrains[TerrainTypes[sec->GetTexture(plane)]].MoveFactor;
+	return movefactor != 0 ? movefactor : ORIG_FRICTION_FACTOR;
 }
 
 //==========================================================================
@@ -584,11 +586,11 @@ int P_GetFriction(const AActor *mo, int *frictionfactor)
 					mo->z < rover->bottom.plane->ZatPoint(mo->x, mo->y))
 					continue;
 
-				newfriction = secfriction(rover->model);
+				newfriction = secfriction(rover->model, rover->top.isceiling);
 				if (newfriction < friction || friction == ORIG_FRICTION)
 				{
 					friction = newfriction;
-					movefactor = secmovefac(rover->model) >> 1;
+					movefactor = secmovefac(rover->model, rover->top.isceiling) >> 1;
 				}
 			}
 	}
@@ -622,11 +624,11 @@ int P_GetFriction(const AActor *mo, int *frictionfactor)
 				else
 					continue;
 
-				newfriction = secfriction(rover->model);
+				newfriction = secfriction(rover->model, rover->top.isceiling);
 				if (newfriction < friction || friction == ORIG_FRICTION)
 				{
 					friction = newfriction;
-					movefactor = secmovefac(rover->model);
+					movefactor = secmovefac(rover->model, rover->top.isceiling);
 				}
 			}