diff --git a/src/actorinlines.h b/src/actorinlines.h
new file mode 100644
index 0000000000..d55ca1b55c
--- /dev/null
+++ b/src/actorinlines.h
@@ -0,0 +1,55 @@
+#pragma once
+
+#include "actor.h"
+#include "r_defs.h"
+// These depend on both actor.h and r_defs.h so they cannot be in either file without creating a cross dependency.
+
+inline DVector3 AActor::PosRelative(int portalgroup) const
+{
+	return Pos() + Displacements.getOffset(Sector->PortalGroup, portalgroup);
+}
+
+inline DVector3 AActor::PosRelative(const AActor *other) const
+{
+	return Pos() + Displacements.getOffset(Sector->PortalGroup, other->Sector->PortalGroup);
+}
+
+inline DVector3 AActor::PosRelative(sector_t *sec) const
+{
+	return Pos() + Displacements.getOffset(Sector->PortalGroup, sec->PortalGroup);
+}
+
+inline DVector3 AActor::PosRelative(line_t *line) const
+{
+	return Pos() + Displacements.getOffset(Sector->PortalGroup, line->frontsector->PortalGroup);
+}
+
+inline DVector3 PosRelative(const DVector3 &pos, line_t *line, sector_t *refsec = NULL)
+{
+	return pos + Displacements.getOffset(refsec->PortalGroup, line->frontsector->PortalGroup);
+}
+
+
+inline void AActor::ClearInterpolation()
+{
+	Prev = Pos();
+	PrevAngles = Angles;
+	if (Sector) PrevPortalGroup = Sector->PortalGroup;
+	else PrevPortalGroup = 0;
+}
+
+inline double secplane_t::ZatPoint(const AActor *ac) const
+{
+	return (D + normal.X*ac->X() + normal.Y*ac->Y()) * negiC;
+}
+
+inline double sector_t::HighestCeilingAt(AActor *a, sector_t **resultsec)
+{
+	return HighestCeilingAt(a->Pos(), resultsec);
+}
+
+inline double sector_t::LowestFloorAt(AActor *a, sector_t **resultsec)
+{
+	return LowestFloorAt(a->Pos(), resultsec);
+}
+
diff --git a/src/dobject.h b/src/dobject.h
index 2adb0b5e4e..f12bfc5014 100644
--- a/src/dobject.h
+++ b/src/dobject.h
@@ -185,236 +185,7 @@ protected: \
 #define _X_VMEXPORT_true(cls)		nullptr
 #define _X_VMEXPORT_false(cls)		nullptr
 
-enum EObjectFlags
-{
-	// GC flags
-	OF_White0			= 1 << 0,		// Object is white (type 0)
-	OF_White1			= 1 << 1,		// Object is white (type 1)
-	OF_Black			= 1 << 2,		// Object is black
-	OF_Fixed			= 1 << 3,		// Object is fixed (should not be collected)
-	OF_Rooted			= 1 << 4,		// Object is soft-rooted
-	OF_EuthanizeMe		= 1 << 5,		// Object wants to die
-	OF_Cleanup			= 1 << 6,		// Object is now being deleted by the collector
-	OF_YesReallyDelete	= 1 << 7,		// Object is being deleted outside the collector, and this is okay, so don't print a warning
-
-	OF_WhiteBits		= OF_White0 | OF_White1,
-	OF_MarkBits			= OF_WhiteBits | OF_Black,
-
-	// Other flags
-	OF_JustSpawned		= 1 << 8,		// Thinker was spawned this tic
-	OF_SerialSuccess	= 1 << 9,		// For debugging Serialize() calls
-	OF_Sentinel			= 1 << 10,		// Object is serving as the sentinel in a ring list
-	OF_Transient		= 1 << 11,		// Object should not be archived (references to it will be nulled on disk)
-	OF_Spawned			= 1 << 12,      // Thinker was spawned at all (some thinkers get deleted before spawning)
-	OF_Released			= 1 << 13,		// Object was released from the GC system and should not be processed by GC function
-	OF_Abstract			= 1 << 14,		// Marks a class that cannot be created with new() function at all
-	OF_UI				= 1 << 15,		// Marks a class that defaults to VARF_UI for it's fields/methods
-	OF_Play				= 1 << 16,		// Marks a class that defaults to VARF_Play for it's fields/methods
-};
-
-template<class T> class TObjPtr;
-
-namespace GC
-{
-	enum EGCState
-	{
-		GCS_Pause,
-		GCS_Propagate,
-		GCS_Sweep,
-		GCS_Finalize
-	};
-
-	// Number of bytes currently allocated through M_Malloc/M_Realloc.
-	extern size_t AllocBytes;
-
-	// Amount of memory to allocate before triggering a collection.
-	extern size_t Threshold;
-
-	// List of gray objects.
-	extern DObject *Gray;
-
-	// List of every object.
-	extern DObject *Root;
-
-	// Current white value for potentially-live objects.
-	extern uint32_t CurrentWhite;
-
-	// Current collector state.
-	extern EGCState State;
-
-	// Position of GC sweep in the list of objects.
-	extern DObject **SweepPos;
-
-	// Size of GC pause.
-	extern int Pause;
-
-	// Size of GC steps.
-	extern int StepMul;
-
-	// Is this the final collection just before exit?
-	extern bool FinalGC;
-
-	// Current white value for known-dead objects.
-	static inline uint32_t OtherWhite()
-	{
-		return CurrentWhite ^ OF_WhiteBits;
-	}
-
-	// Frees all objects, whether they're dead or not.
-	void FreeAll();
-
-	// Does one collection step.
-	void Step();
-
-	// Does a complete collection.
-	void FullGC();
-
-	// Handles the grunt work for a write barrier.
-	void Barrier(DObject *pointing, DObject *pointed);
-
-	// Handles a write barrier.
-	static inline void WriteBarrier(DObject *pointing, DObject *pointed);
-
-	// Handles a write barrier for a pointer that isn't inside an object.
-	static inline void WriteBarrier(DObject *pointed);
-
-	// Handles a read barrier.
-	template<class T> inline T *ReadBarrier(T *&obj)
-	{
-		if (obj == NULL || !(obj->ObjectFlags & OF_EuthanizeMe))
-		{
-			return obj;
-		}
-		return obj = NULL;
-	}
-
-	// Check if it's time to collect, and do a collection step if it is.
-	static inline void CheckGC()
-	{
-		if (AllocBytes >= Threshold)
-			Step();
-	}
-
-	// Forces a collection to start now.
-	static inline void StartCollection()
-	{
-		Threshold = AllocBytes;
-	}
-
-	// Marks a white object gray. If the object wants to die, the pointer
-	// is NULLed instead.
-	void Mark(DObject **obj);
-
-	// Marks an array of objects.
-	void MarkArray(DObject **objs, size_t count);
-
-	// For cleanup
-	void DelSoftRootHead();
-
-	// Soft-roots an object.
-	void AddSoftRoot(DObject *obj);
-
-	// Unroots an object.
-	void DelSoftRoot(DObject *obj);
-
-	template<class T> void Mark(T *&obj)
-	{
-		union
-		{
-			T *t;
-			DObject *o;
-		};
-		o = obj;
-		Mark(&o);
-		obj = t;
-	}
-	template<class T> void Mark(TObjPtr<T> &obj);
-
-	template<class T> void MarkArray(T **obj, size_t count)
-	{
-		MarkArray((DObject **)(obj), count);
-	}
-	template<class T> void MarkArray(TArray<T> &arr)
-	{
-		MarkArray(&arr[0], arr.Size());
-	}
-}
-
-// A template class to help with handling read barriers. It does not
-// handle write barriers, because those can be handled more efficiently
-// with knowledge of the object that holds the pointer.
-template<class T>
-class TObjPtr
-{
-	union
-	{
-		T pp;
-		DObject *o;
-	};
-public:
-	TObjPtr() throw()
-	{
-	}
-	TObjPtr(T q) throw()
-		: pp(q)
-	{
-	}
-	TObjPtr(const TObjPtr<T> &q) throw()
-		: pp(q.pp)
-	{
-	}
-	T operator=(T q) throw()
-	{
-		return pp = q;
-		// The caller must now perform a write barrier.
-	}
-	operator T() throw()
-	{
-		return GC::ReadBarrier(pp);
-	}
-	T &operator*()
-	{
-		T q = GC::ReadBarrier(pp);
-		assert(q != NULL);
-		return *q;
-	}
-	T *operator&() throw()
-	{
-		// Does not perform a read barrier. The only real use for this is with
-		// the DECLARE_POINTER macro, where a read barrier would be a very bad
-		// thing.
-		return &pp;
-	}
-	T operator->() throw()
-	{
-		return GC::ReadBarrier(pp);
-	}
-	bool operator!=(T u) throw()
-	{
-		return GC::ReadBarrier(o) != u;
-	}
-	bool operator==(T u) throw()
-	{
-		return GC::ReadBarrier(o) == u;
-	}
-
-	template<class U> friend inline void GC::Mark(TObjPtr<U> &obj);
-	template<class U> friend FSerializer &Serialize(FSerializer &arc, const char *key, TObjPtr<U> &value, TObjPtr<U> *);
-
-	friend class DObject;
-};
-
-// Use barrier_cast instead of static_cast when you need to cast
-// the contents of a TObjPtr to a related type.
-template<class T,class U> inline T barrier_cast(TObjPtr<U> &o)
-{
-	return static_cast<T>(static_cast<U>(o));
-}
-
-template<class T> inline void GC::Mark(TObjPtr<T> &obj)
-{
-	GC::Mark(&obj.o);
-}
+#include "dobjgc.h"
 
 class DObject
 {
diff --git a/src/dobjgc.h b/src/dobjgc.h
new file mode 100644
index 0000000000..cc5f210b3c
--- /dev/null
+++ b/src/dobjgc.h
@@ -0,0 +1,235 @@
+#pragma once
+#include <stdint.h>
+class DObject;
+class FSerializer;
+
+enum EObjectFlags
+{
+	// GC flags
+	OF_White0			= 1 << 0,		// Object is white (type 0)
+	OF_White1			= 1 << 1,		// Object is white (type 1)
+	OF_Black			= 1 << 2,		// Object is black
+	OF_Fixed			= 1 << 3,		// Object is fixed (should not be collected)
+	OF_Rooted			= 1 << 4,		// Object is soft-rooted
+	OF_EuthanizeMe		= 1 << 5,		// Object wants to die
+	OF_Cleanup			= 1 << 6,		// Object is now being deleted by the collector
+	OF_YesReallyDelete	= 1 << 7,		// Object is being deleted outside the collector, and this is okay, so don't print a warning
+
+	OF_WhiteBits		= OF_White0 | OF_White1,
+	OF_MarkBits			= OF_WhiteBits | OF_Black,
+
+	// Other flags
+	OF_JustSpawned		= 1 << 8,		// Thinker was spawned this tic
+	OF_SerialSuccess	= 1 << 9,		// For debugging Serialize() calls
+	OF_Sentinel			= 1 << 10,		// Object is serving as the sentinel in a ring list
+	OF_Transient		= 1 << 11,		// Object should not be archived (references to it will be nulled on disk)
+	OF_Spawned			= 1 << 12,      // Thinker was spawned at all (some thinkers get deleted before spawning)
+	OF_Released			= 1 << 13,		// Object was released from the GC system and should not be processed by GC function
+	OF_Abstract			= 1 << 14,		// Marks a class that cannot be created with new() function at all
+	OF_UI				= 1 << 15,		// Marks a class that defaults to VARF_UI for it's fields/methods
+	OF_Play				= 1 << 16,		// Marks a class that defaults to VARF_Play for it's fields/methods
+};
+
+template<class T> class TObjPtr;
+
+namespace GC
+{
+	enum EGCState
+	{
+		GCS_Pause,
+		GCS_Propagate,
+		GCS_Sweep,
+		GCS_Finalize
+	};
+
+	// Number of bytes currently allocated through M_Malloc/M_Realloc.
+	extern size_t AllocBytes;
+
+	// Amount of memory to allocate before triggering a collection.
+	extern size_t Threshold;
+
+	// List of gray objects.
+	extern DObject *Gray;
+
+	// List of every object.
+	extern DObject *Root;
+
+	// Current white value for potentially-live objects.
+	extern uint32_t CurrentWhite;
+
+	// Current collector state.
+	extern EGCState State;
+
+	// Position of GC sweep in the list of objects.
+	extern DObject **SweepPos;
+
+	// Size of GC pause.
+	extern int Pause;
+
+	// Size of GC steps.
+	extern int StepMul;
+
+	// Is this the final collection just before exit?
+	extern bool FinalGC;
+
+	// Current white value for known-dead objects.
+	static inline uint32_t OtherWhite()
+	{
+		return CurrentWhite ^ OF_WhiteBits;
+	}
+
+	// Frees all objects, whether they're dead or not.
+	void FreeAll();
+
+	// Does one collection step.
+	void Step();
+
+	// Does a complete collection.
+	void FullGC();
+
+	// Handles the grunt work for a write barrier.
+	void Barrier(DObject *pointing, DObject *pointed);
+
+	// Handles a write barrier.
+	static inline void WriteBarrier(DObject *pointing, DObject *pointed);
+
+	// Handles a write barrier for a pointer that isn't inside an object.
+	static inline void WriteBarrier(DObject *pointed);
+
+	// Handles a read barrier.
+	template<class T> inline T *ReadBarrier(T *&obj)
+	{
+		if (obj == NULL || !(obj->ObjectFlags & OF_EuthanizeMe))
+		{
+			return obj;
+		}
+		return obj = NULL;
+	}
+
+	// Check if it's time to collect, and do a collection step if it is.
+	static inline void CheckGC()
+	{
+		if (AllocBytes >= Threshold)
+			Step();
+	}
+
+	// Forces a collection to start now.
+	static inline void StartCollection()
+	{
+		Threshold = AllocBytes;
+	}
+
+	// Marks a white object gray. If the object wants to die, the pointer
+	// is NULLed instead.
+	void Mark(DObject **obj);
+
+	// Marks an array of objects.
+	void MarkArray(DObject **objs, size_t count);
+
+	// For cleanup
+	void DelSoftRootHead();
+
+	// Soft-roots an object.
+	void AddSoftRoot(DObject *obj);
+
+	// Unroots an object.
+	void DelSoftRoot(DObject *obj);
+
+	template<class T> void Mark(T *&obj)
+	{
+		union
+		{
+			T *t;
+			DObject *o;
+		};
+		o = obj;
+		Mark(&o);
+		obj = t;
+	}
+	template<class T> void Mark(TObjPtr<T> &obj);
+
+	template<class T> void MarkArray(T **obj, size_t count)
+	{
+		MarkArray((DObject **)(obj), count);
+	}
+	template<class T> void MarkArray(TArray<T> &arr)
+	{
+		MarkArray(&arr[0], arr.Size());
+	}
+}
+
+// A template class to help with handling read barriers. It does not
+// handle write barriers, because those can be handled more efficiently
+// with knowledge of the object that holds the pointer.
+template<class T>
+class TObjPtr
+{
+	union
+	{
+		T pp;
+		DObject *o;
+	};
+public:
+	TObjPtr() throw()
+	{
+	}
+	TObjPtr(T q) throw()
+		: pp(q)
+	{
+	}
+	TObjPtr(const TObjPtr<T> &q) throw()
+		: pp(q.pp)
+	{
+	}
+	T operator=(T q) throw()
+	{
+		return pp = q;
+		// The caller must now perform a write barrier.
+	}
+	operator T() throw()
+	{
+		return GC::ReadBarrier(pp);
+	}
+	T &operator*()
+	{
+		T q = GC::ReadBarrier(pp);
+		assert(q != NULL);
+		return *q;
+	}
+	T *operator&() throw()
+	{
+		// Does not perform a read barrier. The only real use for this is with
+		// the DECLARE_POINTER macro, where a read barrier would be a very bad
+		// thing.
+		return &pp;
+	}
+	T operator->() throw()
+	{
+		return GC::ReadBarrier(pp);
+	}
+	bool operator!=(T u) throw()
+	{
+		return GC::ReadBarrier(o) != u;
+	}
+	bool operator==(T u) throw()
+	{
+		return GC::ReadBarrier(o) == u;
+	}
+
+	template<class U> friend inline void GC::Mark(TObjPtr<U> &obj);
+	template<class U> friend FSerializer &Serialize(FSerializer &arc, const char *key, TObjPtr<U> &value, TObjPtr<U> *);
+
+	friend class DObject;
+};
+
+// Use barrier_cast instead of static_cast when you need to cast
+// the contents of a TObjPtr to a related type.
+template<class T,class U> inline T barrier_cast(TObjPtr<U> &o)
+{
+	return static_cast<T>(static_cast<U>(o));
+}
+
+template<class T> inline void GC::Mark(TObjPtr<T> &obj)
+{
+	GC::Mark(&obj.o);
+}
diff --git a/src/g_inventory/a_pickups.h b/src/g_inventory/a_pickups.h
index eb9731ddcf..cbcb2d9cd1 100644
--- a/src/g_inventory/a_pickups.h
+++ b/src/g_inventory/a_pickups.h
@@ -9,7 +9,16 @@
 
 class player_t;
 class FConfigFile;
-struct visstyle_t;
+
+// This encapsulates the fields of vissprite_t that can be altered by AlterWeaponSprite
+struct visstyle_t
+{
+	bool			Invert;
+	float			Alpha;
+	ERenderStyle	RenderStyle;
+};
+
+
 
 /************************************************************************/
 /* Class definitions													*/
diff --git a/src/g_levellocals.h b/src/g_levellocals.h
index 4019064366..98ccdc3e88 100644
--- a/src/g_levellocals.h
+++ b/src/g_levellocals.h
@@ -2,6 +2,7 @@
 
 #include "g_level.h"
 #include "r_defs.h"
+#include "portal.h"
 
 struct FLevelLocals
 {
@@ -136,3 +137,56 @@ inline int sector_t::GetOppositePortalGroup(int plane)
 {
 	return level.sectorPortals[Portals[plane]].mDestination->PortalGroup;
 }
+
+inline bool sector_t::PortalBlocksView(int plane)
+{
+	if (GetPortalType(plane) != PORTS_LINKEDPORTAL) return false;
+	return !!(planes[plane].Flags & (PLANEF_NORENDER | PLANEF_DISABLED | PLANEF_OBSTRUCTED));
+}
+
+inline bool sector_t::PortalBlocksSight(int plane)
+{
+	return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_NORENDER | PLANEF_NOPASS | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
+}
+
+inline bool sector_t::PortalBlocksMovement(int plane)
+{
+	return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_NOPASS | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
+}
+
+inline bool sector_t::PortalBlocksSound(int plane)
+{
+	return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_BLOCKSOUND | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
+}
+
+inline bool sector_t::PortalIsLinked(int plane)
+{
+	return (GetPortalType(plane) == PORTS_LINKEDPORTAL);
+}
+
+inline FLinePortal *line_t::getPortal() const
+{
+	return portalindex >= linePortals.Size() ? (FLinePortal*)NULL : &linePortals[portalindex];
+}
+
+// returns true if the portal is crossable by actors
+inline bool line_t::isLinePortal() const
+{
+	return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_PASSABLE);
+}
+
+// returns true if the portal needs to be handled by the renderer
+inline bool line_t::isVisualPortal() const
+{
+	return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_VISIBLE);
+}
+
+inline line_t *line_t::getPortalDestination() const
+{
+	return portalindex >= linePortals.Size() ? (line_t*)NULL : linePortals[portalindex].mDestination;
+}
+
+inline int line_t::getPortalAlignment() const
+{
+	return portalindex >= linePortals.Size() ? 0 : linePortals[portalindex].mAlign;
+}
diff --git a/src/g_statusbar/sbar.h b/src/g_statusbar/sbar.h
index c9b2178727..689bdc4ac8 100644
--- a/src/g_statusbar/sbar.h
+++ b/src/g_statusbar/sbar.h
@@ -38,6 +38,7 @@
 #include "dobject.h"
 #include "v_collection.h"
 #include "v_text.h"
+#include "r_data/renderstyle.h"
 
 class player_t;
 struct FRemapTable;
diff --git a/src/gl/data/gl_vertexbuffer.h b/src/gl/data/gl_vertexbuffer.h
index f777118fd4..a7e1cd6660 100644
--- a/src/gl/data/gl_vertexbuffer.h
+++ b/src/gl/data/gl_vertexbuffer.h
@@ -31,6 +31,7 @@ struct vertex_t;
 struct secplane_t;
 struct subsector_t;
 struct sector_t;
+class FMaterial;
 
 enum
 {
diff --git a/src/gl/dynlights/a_dynlight.cpp b/src/gl/dynlights/a_dynlight.cpp
index d5a07f089c..6e3f6681c9 100644
--- a/src/gl/dynlights/a_dynlight.cpp
+++ b/src/gl/dynlights/a_dynlight.cpp
@@ -72,6 +72,7 @@
 #include "doomstat.h"
 #include "serializer.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 
 #include "gl/renderer/gl_renderer.h"
diff --git a/src/gl/dynlights/gl_dynlight.h b/src/gl/dynlights/gl_dynlight.h
index 15d9ba6103..8d339f3118 100644
--- a/src/gl/dynlights/gl_dynlight.h
+++ b/src/gl/dynlights/gl_dynlight.h
@@ -26,6 +26,7 @@
 #include "c_cvars.h"
 #include "gl/utility/gl_geometric.h"
 #include "gl/utility/gl_cycler.h"
+#include "actor.h"
 
 
 EXTERN_CVAR(Bool, gl_lights)
diff --git a/src/gl/scene/gl_bsp.cpp b/src/gl/scene/gl_bsp.cpp
index 5c14dbfc09..86efce9920 100644
--- a/src/gl/scene/gl_bsp.cpp
+++ b/src/gl/scene/gl_bsp.cpp
@@ -33,6 +33,7 @@
 #include "p_effect.h"
 #include "po_man.h"
 #include "doomdata.h"
+#include "g_levellocals.h"
 
 #include "gl/renderer/gl_renderer.h"
 #include "gl/data/gl_data.h"
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index 61d146dd15..2e539e7a4d 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -36,6 +36,7 @@
 #include "portal.h"
 #include "templates.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 #include "gl/system/gl_interface.h"
 #include "gl/system/gl_cvars.h"
diff --git a/src/gl/scene/gl_walls_draw.cpp b/src/gl/scene/gl_walls_draw.cpp
index 34a4cc2825..ea75dd39a9 100644
--- a/src/gl/scene/gl_walls_draw.cpp
+++ b/src/gl/scene/gl_walls_draw.cpp
@@ -25,6 +25,8 @@
 #include "p_lnspec.h"
 #include "a_sharedglobal.h"
 #include "g_levellocals.h"
+#include "actor.h"
+#include "actorinlines.h"
 #include "gl/gl_functions.h"
 
 #include "gl/system/gl_interface.h"
diff --git a/src/gl/system/gl_load.c b/src/gl/system/gl_load.c
index 3e494f95a6..7075d69698 100644
--- a/src/gl/system/gl_load.c
+++ b/src/gl/system/gl_load.c
@@ -42,8 +42,12 @@ static void* PosixGetProcAddress (const GLubyte* name)
 
 #if defined(_WIN32)
 
+#ifdef APIENTRY
+#undef APIENTRY
+#endif
 #include <windows.h>
 
+
 #ifdef _MSC_VER
 // disable inlining here because it creates an incredible amount of bloat in this file.
 #pragma inline_depth(0)
diff --git a/src/gl/system/gl_swframebuffer.h b/src/gl/system/gl_swframebuffer.h
index 387b023b2e..b5631074c4 100644
--- a/src/gl/system/gl_swframebuffer.h
+++ b/src/gl/system/gl_swframebuffer.h
@@ -7,6 +7,7 @@
 #endif
 
 #include "SkylineBinPack.h"
+#include "textures.h"
 
 #include <memory>
 
diff --git a/src/gl/textures/gl_hirestex.cpp b/src/gl/textures/gl_hirestex.cpp
index 67287ced0e..151ca5660d 100644
--- a/src/gl/textures/gl_hirestex.cpp
+++ b/src/gl/textures/gl_hirestex.cpp
@@ -42,6 +42,7 @@
 #include "doomstat.h"
 #include "d_main.h"
 #include "zstring.h"
+#include "textures.h"
 
 #ifndef _WIN32
 #define _access(a,b)	access(a,b)
diff --git a/src/gl/textures/gl_texture.h b/src/gl/textures/gl_texture.h
index ebdaa16b85..0cafab7537 100644
--- a/src/gl/textures/gl_texture.h
+++ b/src/gl/textures/gl_texture.h
@@ -2,6 +2,7 @@
 #define __GL_TEXTURE_H__
 
 #include "r_defs.h"
+#include "textures.h"
 
 class FBrightmapTexture : public FTexture
 {
diff --git a/src/m_misc.cpp b/src/m_misc.cpp
index 40214f3620..229835405b 100644
--- a/src/m_misc.cpp
+++ b/src/m_misc.cpp
@@ -32,6 +32,8 @@
 #include <stdlib.h>
 #include <time.h>
 
+#include "r_defs.h"
+
 #include "doomtype.h"
 #include "version.h"
 
@@ -41,6 +43,7 @@
 #include <unistd.h>
 #endif
 
+
 #include <ctype.h>
 
 #include "doomdef.h"
@@ -57,7 +60,6 @@
 #include "i_system.h"
 #include "i_video.h"
 #include "v_video.h"
-#include "r_defs.h"
 
 #include "hu_stuff.h"
 
diff --git a/src/p_3dfloors.h b/src/p_3dfloors.h
index 4d52f550b4..cc3f71a17a 100644
--- a/src/p_3dfloors.h
+++ b/src/p_3dfloors.h
@@ -58,6 +58,7 @@ struct secplane_t;
 struct FDynamicColormap;
 struct line_t;
 struct sector_t;
+class AActor;
 
 struct F3DFloor
 {
diff --git a/src/p_3dmidtex.cpp b/src/p_3dmidtex.cpp
index 4cfe01f19f..0a4c5507de 100644
--- a/src/p_3dmidtex.cpp
+++ b/src/p_3dmidtex.cpp
@@ -42,6 +42,7 @@
 #include "p_maputl.h"
 #include "p_spec.h"
 #include "g_levellocals.h"
+#include "actor.h"
 
 
 //============================================================================
diff --git a/src/p_ceiling.cpp b/src/p_ceiling.cpp
index b978fd0d32..4c2c509e8f 100644
--- a/src/p_ceiling.cpp
+++ b/src/p_ceiling.cpp
@@ -32,6 +32,7 @@
 #include "serializer.h"
 #include "p_spec.h"
 #include "g_levellocals.h"
+#include "textures.h"
 
 //============================================================================
 //
diff --git a/src/p_enemy.cpp b/src/p_enemy.cpp
index dde4fce29c..91d99791dd 100644
--- a/src/p_enemy.cpp
+++ b/src/p_enemy.cpp
@@ -53,6 +53,7 @@
 #include "math/cmath.h"
 #include "g_levellocals.h"
 #include "virtual.h"
+#include "actorinlines.h"
 
 #include "gi.h"
 
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 73cda449c7..1aa762dbdd 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -64,6 +64,7 @@
 #include "g_level.h"
 #include "r_sky.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 CVAR(Bool, cl_bloodsplats, true, CVAR_ARCHIVE)
 CVAR(Int, sv_smartaim, 0, CVAR_ARCHIVE | CVAR_SERVERINFO)
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index c4fe47f31a..e639c440e7 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -39,6 +39,7 @@
 #include "p_3dmidtex.h"
 #include "p_blockmap.h"
 #include "r_utility.h"
+#include "actor.h"
 
 // State.
 #include "r_state.h"
diff --git a/src/p_maputl.h b/src/p_maputl.h
index 99a9acc331..8ac3ea76af 100644
--- a/src/p_maputl.h
+++ b/src/p_maputl.h
@@ -7,6 +7,7 @@
 #include "m_bbox.h"
 
 extern int validcount;
+struct FBlockNode;
 
 struct divline_t
 {
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 5606a1102d..5bac8847f2 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -72,6 +72,7 @@
 #include "g_levellocals.h"
 #include "a_morph.h"
 #include "events.h"
+#include "actorinlines.h"
 
 // MACROS ------------------------------------------------------------------
 
diff --git a/src/p_pspr.h b/src/p_pspr.h
index 311a241c4f..656cc67a9b 100644
--- a/src/p_pspr.h
+++ b/src/p_pspr.h
@@ -31,6 +31,7 @@
 #define WEAPONTOP				32.
 #define WEAPON_FUDGE_Y			0.375
 class AInventory;
+struct FTranslatedLineTarget;
 
 //
 // Overlay psprites are scaled shapes
diff --git a/src/p_pusher.cpp b/src/p_pusher.cpp
index af63467106..0b08b4f65b 100644
--- a/src/p_pusher.cpp
+++ b/src/p_pusher.cpp
@@ -33,6 +33,7 @@
 #include "p_local.h"
 #include "d_player.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 CVAR(Bool, var_pushers, true, CVAR_SERVERINFO);
 
diff --git a/src/p_secnodes.cpp b/src/p_secnodes.cpp
index b351f0e580..346f5ff8e7 100644
--- a/src/p_secnodes.cpp
+++ b/src/p_secnodes.cpp
@@ -26,6 +26,7 @@
 #include "p_maputl.h"
 #include "p_blockmap.h"
 #include "memarena.h"
+#include "actor.h"
 
 //=============================================================================
 // phares 3/21/98
diff --git a/src/p_sight.cpp b/src/p_sight.cpp
index 68bf2ed3d0..d666bc3e96 100644
--- a/src/p_sight.cpp
+++ b/src/p_sight.cpp
@@ -30,6 +30,7 @@
 
 #include "stats.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 static FRandom pr_botchecksight ("BotCheckSight");
 static FRandom pr_checksight ("CheckSight");
diff --git a/src/p_slopes.cpp b/src/p_slopes.cpp
index c574d189b3..cec49003d2 100644
--- a/src/p_slopes.cpp
+++ b/src/p_slopes.cpp
@@ -39,6 +39,7 @@
 #include "p_maputl.h"
 #include "p_spec.h"
 #include "g_levellocals.h"
+#include "actor.h"
 
 //===========================================================================
 //
diff --git a/src/p_spec.h b/src/p_spec.h
index 8d6e53a23a..48535d0b03 100644
--- a/src/p_spec.h
+++ b/src/p_spec.h
@@ -31,6 +31,7 @@
 
 class FScanner;
 struct level_info_t;
+struct FDoorAnimation;
 
 struct FThinkerCollection
 {
diff --git a/src/p_switch.cpp b/src/p_switch.cpp
index ef700b05bf..d23e30ea22 100644
--- a/src/p_switch.cpp
+++ b/src/p_switch.cpp
@@ -49,6 +49,9 @@
 #include "serializer.h"
 #include "p_maputl.h"
 #include "p_spec.h"
+#include "textures.h"
+#include "actor.h"
+#include "actorinlines.h"
 
 #include "gi.h"
 
diff --git a/src/p_terrain.cpp b/src/p_terrain.cpp
index bacd81da3b..b044b3066c 100644
--- a/src/p_terrain.cpp
+++ b/src/p_terrain.cpp
@@ -46,6 +46,7 @@
 #include "s_sound.h"
 #include "p_local.h"
 #include "templates.h"
+#include "actor.h"
 
 // MACROS ------------------------------------------------------------------
 
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 4d5e00e48a..edb3b5364b 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -49,6 +49,7 @@
 #include "p_tags.h"
 #include "p_terrain.h"
 #include "g_levellocals.h"
+#include "info.h"
 
 //===========================================================================
 //
diff --git a/src/po_man.cpp b/src/po_man.cpp
index a5e47401fe..5572db1fa0 100644
--- a/src/po_man.cpp
+++ b/src/po_man.cpp
@@ -33,6 +33,7 @@
 #include "r_utility.h"
 #include "p_blockmap.h"
 #include "g_levellocals.h"
+#include "actorinlines.h"
 
 // MACROS ------------------------------------------------------------------
 
diff --git a/src/po_man.h b/src/po_man.h
index d9e42c7fb4..4bf56a147d 100644
--- a/src/po_man.h
+++ b/src/po_man.h
@@ -4,6 +4,7 @@
 #include "tarray.h"
 #include "r_defs.h"
 #include "m_bbox.h"
+#include "dthinker.h"
 
 class DPolyAction : public DThinker
 {
diff --git a/src/polyrenderer/scene/poly_wall.cpp b/src/polyrenderer/scene/poly_wall.cpp
index e64d1f6c6c..2e42bb4883 100644
--- a/src/polyrenderer/scene/poly_wall.cpp
+++ b/src/polyrenderer/scene/poly_wall.cpp
@@ -33,6 +33,7 @@
 #include "polyrenderer/poly_renderer.h"
 #include "r_sky.h"
 #include "swrenderer/scene/r_light.h"
+#include "g_levellocals.h"
 
 EXTERN_CVAR(Bool, r_drawmirrors)
 
diff --git a/src/r_data/renderstyle.cpp b/src/r_data/renderstyle.cpp
index c44b136a09..49628c881a 100644
--- a/src/r_data/renderstyle.cpp
+++ b/src/r_data/renderstyle.cpp
@@ -35,6 +35,7 @@
 #include "templates.h"
 #include "renderstyle.h"
 #include "c_cvars.h"
+#include "serializer.h"
 
 CVAR (Bool, r_drawtrans, true, 0)
 CVAR (Int, r_drawfuzz, 1, CVAR_ARCHIVE)
@@ -191,3 +192,8 @@ void FRenderStyle::CheckFuzz()
 		BlendOp = STYLEOP_Fuzz;
 	}
 }
+
+FSerializer &Serialize(FSerializer &arc, const char *key, FRenderStyle &style, FRenderStyle *def)
+{
+	return arc.Array(key, &style.BlendOp, def ? &def->BlendOp : nullptr, 4);
+}
diff --git a/src/r_data/voxels.cpp b/src/r_data/voxels.cpp
index e9b30cd79c..70975c7a46 100644
--- a/src/r_data/voxels.cpp
+++ b/src/r_data/voxels.cpp
@@ -62,6 +62,7 @@
 #include "r_data/colormaps.h"
 #include "r_data/sprites.h"
 #include "voxels.h"
+#include "info.h"
 
 void VOX_AddVoxel(int sprnum, int frame, FVoxelDef *def);
 
diff --git a/src/r_defs.h b/src/r_defs.h
index 30d0597d56..bebe16fd6b 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -25,8 +25,8 @@
 
 #include "doomdef.h"
 #include "templates.h"
-#include "memarena.h"
 #include "m_bbox.h"
+#include "dobjgc.h"
 
 // Some more or less basic data types
 // we depend on.
@@ -35,13 +35,15 @@
 // We rely on the thinker data struct
 // to handle sound origins in sectors.
 // SECTORS do store MObjs anyway.
-#include "actor.h"
 struct FLightNode;
 struct FGLSection;
+class FSerializer;
 struct FPortal;
+struct FSectorPortal;
+struct FLinePortal;
 struct seg_t;
-
-#include "dthinker.h"
+struct sector_t;
+class AActor;
 
 #define MAXWIDTH 5760
 #define MAXHEIGHT 3600
@@ -351,11 +353,6 @@ public:
 		return (D + normal.X*v->fX() + normal.Y*v->fY()) * negiC;
 	}
 
-	double ZatPoint(const AActor *ac) const
-	{
-		return (D + normal.X*ac->X() + normal.Y*ac->Y()) * negiC;
-	}
-
 	// Returns the value of z at vertex v if d is equal to dist
 	double ZatPointDist(const vertex_t *v, double dist)
 	{
@@ -434,6 +431,7 @@ public:
 	}
 
 	bool CopyPlaneIfValid (secplane_t *dest, const secplane_t *opp) const;
+	inline double secplane_t::ZatPoint(const AActor *ac) const;
 
 };
 
@@ -875,31 +873,11 @@ public:
 		Flags &= ~SECF_SPECIALFLAGS;
 	}
 
-	bool PortalBlocksView(int plane)
-	{
-		if (GetPortalType(plane) != PORTS_LINKEDPORTAL) return false;
-		return !!(planes[plane].Flags & (PLANEF_NORENDER | PLANEF_DISABLED | PLANEF_OBSTRUCTED));
-	}
-
-	bool PortalBlocksSight(int plane)
-	{
-		return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_NORENDER | PLANEF_NOPASS | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
-	}
-
-	bool PortalBlocksMovement(int plane)
-	{
-		return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_NOPASS | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
-	}
-
-	bool PortalBlocksSound(int plane)
-	{
-		return PLANEF_LINKED != (planes[plane].Flags & (PLANEF_BLOCKSOUND | PLANEF_DISABLED | PLANEF_OBSTRUCTED | PLANEF_LINKED));
-	}
-
-	bool PortalIsLinked(int plane)
-	{
-		return (GetPortalType(plane) == PORTS_LINKEDPORTAL);
-	}
+	inline bool PortalBlocksView(int plane);
+	inline bool PortalBlocksSight(int plane);
+	inline bool PortalBlocksMovement(int plane);
+	inline bool PortalBlocksSound(int plane);
+	inline bool PortalIsLinked(int plane);
 
 	void ClearPortal(int plane)
 	{
@@ -936,16 +914,8 @@ public:
 	double HighestCeilingAt(const DVector2 &a, sector_t **resultsec = NULL);
 	double LowestFloorAt(const DVector2 &a, sector_t **resultsec = NULL);
 
-
-	double HighestCeilingAt(AActor *a, sector_t **resultsec = NULL)
-	{
-		return HighestCeilingAt(a->Pos(), resultsec);
-	}
-
-	double LowestFloorAt(AActor *a, sector_t **resultsec = NULL)
-	{
-		return LowestFloorAt(a->Pos(), resultsec);
-	}
+	inline double HighestCeilingAt(AActor *a, sector_t **resultsec = NULL);
+	inline double LowestFloorAt(AActor *a, sector_t **resultsec = NULL);
 
 	bool isClosed() const
 	{
@@ -1283,32 +1253,11 @@ struct line_t
 
 	FSectorPortal *GetTransferredPortal();
 
-	FLinePortal *getPortal() const
-	{
-		return portalindex >= linePortals.Size() ? (FLinePortal*)NULL : &linePortals[portalindex];
-	}
-
-	// returns true if the portal is crossable by actors
-	bool isLinePortal() const
-	{
-		return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_PASSABLE);
-	}
-
-	// returns true if the portal needs to be handled by the renderer
-	bool isVisualPortal() const
-	{
-		return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_VISIBLE);
-	}
-
-	line_t *getPortalDestination() const
-	{
-		return portalindex >= linePortals.Size() ? (line_t*)NULL : linePortals[portalindex].mDestination;
-	}
-
-	int getPortalAlignment() const
-	{
-		return portalindex >= linePortals.Size() ? 0 : linePortals[portalindex].mAlign;
-	}
+	inline FLinePortal *getPortal() const;
+	inline bool isLinePortal() const;
+	inline bool isVisualPortal() const;
+	inline line_t *getPortalDestination() const;
+	inline int getPortalAlignment() const;
 
 	int Index() const;
 };
@@ -1476,15 +1425,6 @@ struct FMiniBSP
 
 typedef uint8_t lighttable_t;	// This could be wider for >8 bit display.
 
-// This encapsulates the fields of vissprite_t that can be altered by AlterWeaponSprite
-struct visstyle_t
-{
-	bool			Invert;
-	float			Alpha;
-	ERenderStyle	RenderStyle;
-};
-
-
 //----------------------------------------------------------------------------------
 //
 // The playsim can use different nodes than the renderer so this is
@@ -1503,40 +1443,6 @@ inline sector_t *P_PointInSector(double X, double Y)
 	return P_PointInSubsector(X, Y)->sector;
 }
 
-inline DVector3 AActor::PosRelative(int portalgroup) const
-{
-	return Pos() + Displacements.getOffset(Sector->PortalGroup, portalgroup);
-}
-
-inline DVector3 AActor::PosRelative(const AActor *other) const
-{
-	return Pos() + Displacements.getOffset(Sector->PortalGroup, other->Sector->PortalGroup);
-}
-
-inline DVector3 AActor::PosRelative(sector_t *sec) const
-{
-	return Pos() + Displacements.getOffset(Sector->PortalGroup, sec->PortalGroup);
-}
-
-inline DVector3 AActor::PosRelative(line_t *line) const
-{
-	return Pos() + Displacements.getOffset(Sector->PortalGroup, line->frontsector->PortalGroup);
-}
-
-inline DVector3 PosRelative(const DVector3 &pos, line_t *line, sector_t *refsec = NULL)
-{
-	return pos + Displacements.getOffset(refsec->PortalGroup, line->frontsector->PortalGroup);
-}
-
-
-inline void AActor::ClearInterpolation()
-{
-	Prev = Pos();
-	PrevAngles = Angles;
-	if (Sector) PrevPortalGroup = Sector->PortalGroup;
-	else PrevPortalGroup = 0;
-}
-
 inline bool FBoundingBox::inRange(const line_t *ld) const
 {
 	return Left() < ld->bbox[BOXRIGHT] &&
diff --git a/src/r_utility.h b/src/r_utility.h
index f1c1fc60d4..1487371b4f 100644
--- a/src/r_utility.h
+++ b/src/r_utility.h
@@ -109,6 +109,7 @@ void R_SetWindow (int windowSize, int fullWidth, int fullHeight, int stHeight, b
 extern void R_FreePastViewers ();
 extern void R_ClearPastViewer (AActor *actor);
 
+class FCanvasTexture;
 // This list keeps track of the cameras that draw into canvas textures.
 struct FCanvasTextureInfo
 {
diff --git a/src/scripting/vm/vmexec.h b/src/scripting/vm/vmexec.h
index b588d15d34..c24dfa111c 100644
--- a/src/scripting/vm/vmexec.h
+++ b/src/scripting/vm/vmexec.h
@@ -820,7 +820,7 @@ begin:
 			ThrowAbortException(X_OTHER, "Cannot instantiate abstract class %s", cls->TypeName.GetChars());
 		}
 		// Creating actors here must be outright prohibited,
-		if (cls->IsDescendantOf(RUNTIME_CLASS(AActor)))
+		if (cls->IsDescendantOf(NAME_Actor))
 		{
 			ThrowAbortException(X_OTHER, "Cannot create actors with 'new'");
 		}
diff --git a/src/serializer.h b/src/serializer.h
index 7527eeb3c3..cea8df36d8 100644
--- a/src/serializer.h
+++ b/src/serializer.h
@@ -6,6 +6,7 @@
 #include "tarray.h"
 #include "r_defs.h"
 #include "resourcefiles/file_zip.h"
+#include "tflags.h"
 
 extern bool save_full;
 
@@ -14,6 +15,15 @@ struct usercmd_t;
 
 struct FWriter;
 struct FReader;
+class PClass;
+class PClassActor;
+struct FStrifeDialogueNode;
+class FFont;
+struct FState;
+struct FDoorAnimation;
+class FSoundID;
+struct FPolyObj;
+union FRenderStyle;
 
 inline bool nullcmp(const void *buffer, size_t length)
 {
@@ -279,10 +289,7 @@ inline FSerializer &Serialize(FSerializer &arc, const char *key, PalEntry &pe, P
 	return Serialize(arc, key, pe.d, def? &def->d : nullptr);
 }
 
-inline FSerializer &Serialize(FSerializer &arc, const char *key, FRenderStyle &style, FRenderStyle *def)
-{
-	return arc.Array(key, &style.BlendOp, def ? &def->BlendOp : nullptr, 4);
-}
+FSerializer &Serialize(FSerializer &arc, const char *key, FRenderStyle &style, FRenderStyle *def);
 
 template<class T, class TT>
 FSerializer &Serialize(FSerializer &arc, const char *key, TFlags<T, TT> &flags, TFlags<T, TT> *def)
diff --git a/src/swrenderer/drawers/r_draw.h b/src/swrenderer/drawers/r_draw.h
index 29b908398b..3d8d58dc5e 100644
--- a/src/swrenderer/drawers/r_draw.h
+++ b/src/swrenderer/drawers/r_draw.h
@@ -2,6 +2,7 @@
 #pragma once
 
 #include "r_defs.h"
+#include "c_cvars.h"
 #include <memory>
 
 struct FSWColormap;
diff --git a/src/swrenderer/r_memory.h b/src/swrenderer/r_memory.h
index f01d52a4dc..2c7a04874b 100644
--- a/src/swrenderer/r_memory.h
+++ b/src/swrenderer/r_memory.h
@@ -14,6 +14,7 @@
 #pragma once
 
 #include <memory>
+#include <vector>
 
 namespace swrenderer
 {
diff --git a/src/v_collection.cpp b/src/v_collection.cpp
index b7e395e6ae..a9e1772a3a 100644
--- a/src/v_collection.cpp
+++ b/src/v_collection.cpp
@@ -37,6 +37,7 @@
 #include "v_video.h"
 #include "m_swap.h"
 #include "w_wad.h"
+#include "textures.h"
 
 FImageCollection::FImageCollection ()
 {
diff --git a/src/v_collection.h b/src/v_collection.h
index 9c0e8676b0..9e2800319e 100644
--- a/src/v_collection.h
+++ b/src/v_collection.h
@@ -37,6 +37,8 @@
 #include "doomtype.h"
 #include "r_defs.h"
 
+class FTexture;
+
 class FImageCollection
 {
 public:
diff --git a/src/v_draw.cpp b/src/v_draw.cpp
index bcfd8f7677..3f3cae3a27 100644
--- a/src/v_draw.cpp
+++ b/src/v_draw.cpp
@@ -61,6 +61,7 @@
 #include "colormatcher.h"
 #include "r_data/colormaps.h"
 #include "g_levellocals.h"
+#include "textures.h"
 
 CUSTOM_CVAR(Int, uiscale, 2, CVAR_ARCHIVE | CVAR_NOINITCALL)
 {
diff --git a/src/win32/fb_d3d9.cpp b/src/win32/fb_d3d9.cpp
index e8cedef9dc..1056d52fff 100644
--- a/src/win32/fb_d3d9.cpp
+++ b/src/win32/fb_d3d9.cpp
@@ -71,6 +71,7 @@
 #include "doomstat.h"
 #include "v_palette.h"
 #include "w_wad.h"
+#include "textures.h"
 #include "r_data/colormaps.h"
 #include "SkylineBinPack.h"
 #include "swrenderer/scene/r_light.h"