From 0d7bd368face5f2eaac658c89b12ff05b223a248 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@zdoom.fake>
Date: Sun, 17 Apr 2016 15:46:04 +0200
Subject: [PATCH] - added some fudging to draw the outer linedefs of a portal
 area.

This is needed so that polyportals get rendered correctly. For non-polyportals these will normally be outside the portal window and just be discarded.
---
 src/gl/scene/gl_bsp.cpp  | 58 +++++++++++++++++++++++++++++++++-------
 src/gl/scene/gl_portal.h |  4 ++-
 2 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/src/gl/scene/gl_bsp.cpp b/src/gl/scene/gl_bsp.cpp
index a32b8aaa0..bb7cbce4e 100644
--- a/src/gl/scene/gl_bsp.cpp
+++ b/src/gl/scene/gl_bsp.cpp
@@ -95,7 +95,7 @@ static void UnclipSubsector(subsector_t *sub)
 static subsector_t *currentsubsector;
 static sector_t *currentsector;
 
-static void AddLine (seg_t *seg)
+static void AddLine (seg_t *seg, bool portalclip)
 {
 #ifdef _DEBUG
 	if (seg->linedef - lines == 38)
@@ -108,7 +108,7 @@ static void AddLine (seg_t *seg)
 	sector_t * backsector = NULL;
 	sector_t bs;
 
-	if (GLRenderer->mCurrentPortal)
+	if (portalclip)
 	{
 		int clipres = GLRenderer->mCurrentPortal->ClipSeg(seg);
 		if (clipres == GLPortal::PClip_InFront) return;
@@ -215,7 +215,7 @@ static void PolySubsector(subsector_t * sub)
 	{
 		if (line->linedef)
 		{
-			AddLine (line);
+			AddLine (line, GLRenderer->mCurrentPortal != NULL);
 		}
 		line++;
 	}
@@ -310,11 +310,11 @@ static inline void AddLines(subsector_t * sub, sector_t * sector)
 		{
 			if (seg->linedef == NULL)
 			{
-				if (!(sub->flags & SSECF_DRAWN)) AddLine (seg);
+				if (!(sub->flags & SSECF_DRAWN)) AddLine (seg, GLRenderer->mCurrentPortal != NULL);
 			}
 			else if (!(seg->sidedef->Flags & WALLF_POLYOBJ)) 
 			{
-				AddLine (seg);
+				AddLine (seg, GLRenderer->mCurrentPortal != NULL);
 			}
 			seg++;
 		}
@@ -322,6 +322,40 @@ static inline void AddLines(subsector_t * sub, sector_t * sector)
 	ClipWall.Unclock();
 }
 
+//==========================================================================
+//
+// Adds lines that lie directly on the portal boundary.
+// Only two-sided lines will be handled here, and no polyobjects
+//
+//==========================================================================
+
+inline bool PointOnLine(const DVector2 &pos, const line_t *line)
+{
+	double v = (pos.Y - line->v1->fY()) * line->Delta().X + (line->v1->fX() - pos.X) * line->Delta().Y;
+	return fabs(v) <= EQUAL_EPSILON;
+}
+
+static inline void AddSpecialPortalLines(subsector_t * sub, sector_t * sector, line_t *line)
+{
+	currentsector = sector;
+	currentsubsector = sub;
+
+	ClipWall.Clock();
+	int count = sub->numlines;
+	seg_t * seg = sub->firstline;
+
+	while (count--)
+	{
+		if (seg->linedef != NULL && seg->PartnerSeg != NULL)
+		{
+			if (PointOnLine(seg->v1->fPos(), line) && PointOnLine(seg->v2->fPos(), line))
+				AddLine(seg, false);
+		}
+		seg++;
+	}
+	ClipWall.Unclock();
+}
+
 
 //==========================================================================
 //
@@ -395,16 +429,20 @@ static void DoSubsector(subsector_t * sub)
 		UnclipSubsector(sub);
 	}
 
+	fakesector=gl_FakeFlat(sector, &fake, false);
+
 	if (GLRenderer->mCurrentPortal)
 	{
 		int clipres = GLRenderer->mCurrentPortal->ClipSubsector(sub);
-		if (clipres == GLPortal::PClip_InFront) return;
+		if (clipres == GLPortal::PClip_InFront)
+		{
+			line_t *line = GLRenderer->mCurrentPortal->ClipLine();
+			// The subsector is out of range, but we still have to check lines that lie directly on the boundary and may expose their upper or lower parts.
+			if (line) AddSpecialPortalLines(sub, fakesector, line);
+			return;
+		}
 	}
 
-
-
-	fakesector=gl_FakeFlat(sector, &fake, false);
-
 	if (sector->validcount != validcount)
 	{
 		GLRenderer->mVBO->CheckUpdate(sector);
diff --git a/src/gl/scene/gl_portal.h b/src/gl/scene/gl_portal.h
index d8c5da619..f62db377d 100644
--- a/src/gl/scene/gl_portal.h
+++ b/src/gl/scene/gl_portal.h
@@ -137,7 +137,7 @@ public:
 	{
 		PClip_InFront,
 		PClip_Inside,
-		PClip_Behind
+		PClip_Behind,
 	};
 
 	void RenderPortal(bool usestencil, bool doquery)
@@ -165,6 +165,7 @@ public:
 	virtual int ClipSeg(seg_t *seg) { return PClip_Inside; }
 	virtual int ClipSubsector(subsector_t *sub) { return PClip_Inside; }
 	virtual int ClipPoint(const DVector2 &pos) { return PClip_Inside; }
+	virtual line_t *ClipLine() { return NULL; }
 
 	static void BeginScene();
 	static void StartFrame();
@@ -251,6 +252,7 @@ protected:
 	virtual void DrawContents();
 	virtual void * GetSource() const { return glport; }
 	virtual const char *GetName();
+	virtual line_t *ClipLine() { return line(); }
 
 public: