From b91ed5dc5da371cf51722ea6d5f2229712285d59 Mon Sep 17 00:00:00 2001
From: MajorCooke <paul.growney22@gmail.com>
Date: Thu, 5 May 2016 18:33:36 -0500
Subject: [PATCH] Added GetZAt DECORATE function. - float GetZAt(x, y, angle,
 flags, pick_pointer); - Gets the floor z  at x distance ahead and y distance
 to the side in relative form from the calling actor pointer. Flags are as
 follows (GZF_ prefix): - CEILING: Returns the ceiling z instead of floor. -
 ABSOLUTEPOS: x and y are absolute positions. - ABSOLUTEANG: angle parameter
 does not add the pointer's angle to the angle parameter.

---
 src/thingdef/thingdef_codeptr.cpp  | 71 ++++++++++++++++++++++++++++++
 wadsrc/static/actors/actor.txt     |  1 +
 wadsrc/static/actors/constants.txt |  8 ++++
 3 files changed, 80 insertions(+)

diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/thingdef/thingdef_codeptr.cpp
index 677687f3e0..4ceb2b6f49 100644
--- a/src/thingdef/thingdef_codeptr.cpp
+++ b/src/thingdef/thingdef_codeptr.cpp
@@ -386,6 +386,77 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, GetGibHealth)
 	return 0;
 }
 
+//==========================================================================
+//
+// GetZAt
+//
+// NON-ACTION function to get the floor or ceiling z at (x, y) with 
+// relativity being an option.
+//==========================================================================
+enum GZFlags
+{
+	GZF_ABSOLUTEPOS =			1,
+	GZF_ABSOLUTEANG =			1 << 1,
+	GZF_CEILING =				1 << 2,
+};
+
+DEFINE_ACTION_FUNCTION_PARAMS(AActor, GetZAt)
+{
+	if (numret > 0)
+	{
+		assert(ret != NULL);
+		PARAM_SELF_PROLOGUE(AActor);
+		PARAM_FLOAT_OPT(px)			{ px = 0.; }
+		PARAM_FLOAT_OPT(py)			{ py = 0.; }
+		PARAM_ANGLE_OPT(angle)		{ angle = 0.; }
+		PARAM_INT_OPT(flags)		{ flags = 0; }
+		PARAM_INT_OPT(pick_pointer) { pick_pointer = AAPTR_DEFAULT; }
+
+		AActor *mobj = COPY_AAPTR(self, pick_pointer);
+		if (mobj == nullptr)
+		{
+			ret->SetFloat(0);
+		}
+		else
+		{
+			DVector2 pos = { px, py };
+			int secnum;
+			double z = 0.;
+
+			if (!(flags & GZF_ABSOLUTEPOS))
+			{
+				if (!(flags & GZF_ABSOLUTEANG))
+				{
+					angle += mobj->Angles.Yaw;
+				}
+
+				double s = angle.Sin();
+				double c = angle.Cos();
+				pos = mobj->Vec2Offset(pos.X * c + pos.Y * s, pos.X * s - pos.Y * c);
+			}
+
+			secnum = int(P_PointInSector(pos.X, pos.Y) - sectors);
+
+			if (secnum >= 0)
+			{
+				if (flags & GZF_CEILING)
+				{
+					//z = mobj->Sector->ceilingplane.ZatPoint(pos.X, pos.Y);
+					z = sectors[secnum].ceilingplane.ZatPoint(pos);
+				}
+				else
+				{
+					//z = mobj->Sector->floorplane.ZatPoint(pos.X, pos.Y);
+					z = sectors[secnum].floorplane.ZatPoint(pos);
+				}
+			}
+			ret->SetFloat(z);
+			return 1;
+		}
+	}
+	return 0;
+}
+
 //===========================================================================
 //
 // __decorate_internal_state__
diff --git a/wadsrc/static/actors/actor.txt b/wadsrc/static/actors/actor.txt
index 8b35be30d0..44ebb1dc32 100644
--- a/wadsrc/static/actors/actor.txt
+++ b/wadsrc/static/actors/actor.txt
@@ -43,6 +43,7 @@ ACTOR Actor native //: Thinker
 	native int	CountInv(class<Inventory> itemtype, int ptr_select = AAPTR_DEFAULT);
 	native float GetDistance(bool checkz, int ptr = AAPTR_DEFAULT);
 	native float GetAngle(bool relative, int ptr = AAPTR_DEFAULT);
+	native float GetZAt(float px = 0, float py = 0, float angle = 0, int flags = 0, int pick_pointer = AAPTR_DEFAULT);
 	native int GetSpawnHealth();
 	native int GetGibHealth();
 
diff --git a/wadsrc/static/actors/constants.txt b/wadsrc/static/actors/constants.txt
index 1922194edb..a639799aff 100644
--- a/wadsrc/static/actors/constants.txt
+++ b/wadsrc/static/actors/constants.txt
@@ -550,3 +550,11 @@ enum
 	FMDF_INTERPOLATE =		1 << 1,
 	FMDF_NOANGLE =			1 << 2,
 };
+
+// Flags for GetZAt
+enum
+{
+	GZF_ABSOLUTEPOS =			1,
+	GZF_ABSOLUTEANG =			1 << 1,
+	GZF_CEILING =				1 << 2,
+};