Added A_SetViewPos(Vector3 Offset, int Flags = -1)

- Offset: The offset from the actor's view to move the camera about.
 - Flags: (Default is -1, which means don't change flags)
  - VPSF_ABSOLUTEOFFSET: Don't include actor angles in calculation.
  - VPSF_ABSOLUTEPOS: Position is absolute, and disables all transformations. Modders are responsible for being portal aware!

Notes:
- `ViewPos` in Actor will be `null` until A_SetViewPos is called for the first time.

**Issues:**
- Hiding sprite while in portal incomplete.

src/playsim/actor.h

@@ -654,6 +654,63 @@ struct FDropItem
 	int Amount;
 };
 
+enum EViewPosFlags // [MC] Flags for SetViewPos.
+{
+	VPSF_ABSOLUTEOFFSET =	1 << 1,			// Don't include angles.
+	VPSF_ABSOLUTEPOS =		1 << 2,			// Use absolute position.
+};
+
+class FViewPosition : public DObject
+{
+	DECLARE_CLASS(FViewPosition, DObject);
+public:
+	// Variables
+	// Exposed to ZScript
+	DVector3	Offset;
+	int			Flags;
+
+	// Engine only. 
+	// Used to do a backwards trace to disable rendering over portals.
+	bool		isUsed;
+	DVector3	PlrPos,
+				CamPos;
+	double		Distance;
+	sector_t	*CamSec;
+
+
+	// Functions
+	FViewPosition()
+	{
+		Offset = PlrPos = CamPos = { 0,0,0 };
+		isUsed = false;
+		Distance = 0.0;
+		CamSec = nullptr;
+	}
+
+	void Set(DVector3 &off, int f = -1)
+	{
+		Offset = off;
+
+		if (f > -1)
+			Flags = f;
+	}
+
+	bool isZero()
+	{
+		return Offset.isZero();
+	}
+
+	void ResetTraceInfo()
+	{
+		isUsed = false;
+		PlrPos = CamPos = {0,0,0};
+		Distance = 0.;
+		CamSec = nullptr;
+	}
+
+	bool TraceBack(AActor *Owner);
+};
+
 const double MinVel = EQUAL_EPSILON;
 
 // Map Object definition.
@@ -974,7 +1031,8 @@ public:
 	DAngle			SpriteAngle;
 	DAngle			SpriteRotation;
 	DRotator		Angles;
-	DRotator		ViewAngles;			// Offsets for cameras
+	DRotator		ViewAngles;			// Angle offsets for cameras
+	FViewPosition	*ViewPos;			// Position offsets for cameras
 	DVector2		Scale;				// Scaling values; 1 is normal size
 	double			Alpha;				// Since P_CheckSight makes an alpha check this can't be a float. It has to be a double.
 

src/playsim/p_local.h

@@ -50,6 +50,7 @@ struct secplane_t;
 struct FCheckPosition;
 struct FTranslatedLineTarget;
 struct FLinePortal;
+class FViewPosition;
 
 #include <stdlib.h>
 
@@ -392,6 +393,10 @@ void	P_PlaySpawnSound(AActor *missile, AActor *spawner);
 // [RH] Position the chasecam
 void	P_AimCamera (AActor *t1, DVector3 &, DAngle &, sector_t *&sec, bool &unlinked);
 
+// [MC] Aiming for ViewPos
+void	P_AdjustViewPos(AActor *t1, DVector3 orig, DVector3 &, sector_t *&sec, bool &unlinked, FViewPosition *VP);
+
+
 // [RH] Means of death
 enum
 {

src/playsim/p_map.cpp

@@ -5423,6 +5423,62 @@ void P_AimCamera(AActor *t1, DVector3 &campos, DAngle &camangle, sector_t *&Came
 	camangle = trace.SrcAngleFromTarget - 180.;
 }
 
+// [MC] Used for ViewPos. Uses code borrowed from P_AimCamera.
+void P_AdjustViewPos(AActor *t1, DVector3 orig, DVector3 &campos, sector_t *&CameraSector, bool &unlinked, FViewPosition *VP)
+{
+	FTraceResults trace;
+	const DVector3 vvec = campos - orig;
+	const double distance = vvec.Length();
+
+	// Trace handles all of the portal crossing, which is why there is no usage of Vec#Offset(Z).
+	if (Trace(orig, t1->Sector, vvec.Unit(), distance, 0, 0, t1, trace) &&
+		trace.Distance > 5)
+	{
+		// Position camera slightly in front of hit thing
+		campos = orig + vvec.Unit() * (trace.Distance - 5);
+	}
+	else
+	{
+		campos = trace.HitPos - trace.HitVector * 1 / 256.;
+	}
+//	DVector3 cpos = campos;
+	CameraSector = trace.Sector;
+	unlinked = trace.unlinked;
+
+	// Save the info for the renderers. Needed to disable sprites across portals.
+	VP->Distance = distance;
+	VP->isUsed = true;
+}
+
+struct EViewPosFinder
+{
+	AActor *Owner;
+};
+
+static ETraceStatus TraceToOwner(FTraceResults &res, void *userdata)
+{
+	// Try to guarantee hitting the owner if possible.
+	if (res.HitType != TRACE_HitActor)
+		return TRACE_Skip;
+
+	EViewPosFinder *data = (EViewPosFinder *)userdata;
+	ETraceStatus ret = (res.Actor == data->Owner) ? TRACE_Stop : TRACE_Skip;
+	return ret;
+}
+
+bool FViewPosition::TraceBack(AActor *Owner)
+{
+	if (!isUsed || !Owner)
+		return false;
+	
+	DVector3 vvec = (CamPos - PlrPos).Unit() * -1.0;
+	FTraceResults res;
+	EViewPosFinder TrcBack = {Owner};
+
+	bool ret = Trace(CamPos, CamSec, vvec, Distance, 0, 0, nullptr, res, TRACE_ReportPortals, TraceToOwner, &TrcBack);
+	
+	return ret;
+}
 
 //==========================================================================
 //

src/playsim/p_mobj.cpp

@@ -369,6 +369,7 @@ void AActor::Serialize(FSerializer &arc)
 		A("spawnorder", SpawnOrder)
 		A("friction", Friction)
 		A("SpriteOffset", SpriteOffset)
+		("viewpos", ViewPos)
 		A("userlights", UserLights);
 
 		SerializeTerrain(arc, "floorterrain", floorterrain, &def->floorterrain);
@@ -4952,6 +4953,12 @@ void AActor::OnDestroy ()
 	UnlinkFromWorld (nullptr);
 	flags |= MF_NOSECTOR|MF_NOBLOCKMAP;
 
+	if (ViewPos != nullptr)
+	{
+		ViewPos->Destroy();
+		ViewPos = nullptr;
+	}
+
 	// Transform any playing sound into positioned, non-actor sounds.
 	S_RelinkSound (this, NULL);