From 54a120d61247c699405b22c6a55ae606735e1041 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@zdoom.fake>
Date: Sat, 23 Jul 2016 10:23:34 +0200
Subject: [PATCH] - do not process subsectors if rendering a stacked sector
 portal and the clipper is set to 'blocked', i.e. no visible parts are
 present.

This solves the most severe occurences of sprites being drawn in front of a portal's contents. It is not a full fix, though, there's still some extreme cases where portals may glitch if some stuff gets between the camera and the actual portal area.
Normally this has to perform a full check of the subsector against the portal's camera-facing linedefs but that's too costly for those rare cases where it may be an issue.
---
 src/gl/scene/gl_bsp.cpp     |  2 ++
 src/gl/scene/gl_clipper.cpp |  1 +
 src/gl/scene/gl_clipper.h   | 12 ++++++++++++
 src/gl/scene/gl_portal.cpp  |  1 +
 4 files changed, 16 insertions(+)

diff --git a/src/gl/scene/gl_bsp.cpp b/src/gl/scene/gl_bsp.cpp
index b9915dd72..5f95902a3 100644
--- a/src/gl/scene/gl_bsp.cpp
+++ b/src/gl/scene/gl_bsp.cpp
@@ -79,6 +79,7 @@ static void UnclipSubsector(subsector_t *sub)
 		if (startAngle-endAngle >= ANGLE_180)  
 		{
 			clipper.SafeRemoveClipRange(startAngle, endAngle);
+			clipper.SetBlocked(false);
 		}
 		seg++;
 	}
@@ -444,6 +445,7 @@ static void DoSubsector(subsector_t * sub)
 		// range this subsector spans before going on.
 		UnclipSubsector(sub);
 	}
+	if (clipper.IsBlocked()) return;	// if we are inside a stacked sector portal which hasn't unclipped anything yet.
 
 	fakesector=gl_FakeFlat(sector, &fake, false);
 
diff --git a/src/gl/scene/gl_clipper.cpp b/src/gl/scene/gl_clipper.cpp
index a523b27fd..cd076d58a 100644
--- a/src/gl/scene/gl_clipper.cpp
+++ b/src/gl/scene/gl_clipper.cpp
@@ -92,6 +92,7 @@ void Clipper::Clear()
 	ClipNode *node = cliphead;
 	ClipNode *temp;
 	
+	blocked = false;
 	while (node != NULL)
 	{
 		temp = node;
diff --git a/src/gl/scene/gl_clipper.h b/src/gl/scene/gl_clipper.h
index d09a82147..8da75080e 100644
--- a/src/gl/scene/gl_clipper.h
+++ b/src/gl/scene/gl_clipper.h
@@ -54,6 +54,7 @@ class Clipper
 	ClipNode * clipnodes;
 	ClipNode * cliphead;
 	ClipNode * silhouette;	// will be preserved even when RemoveClipRange is called
+	bool blocked;
 
 	static angle_t AngleToPseudo(angle_t ang);
 	bool IsRangeVisible(angle_t startangle, angle_t endangle);
@@ -68,6 +69,7 @@ public:
 
 	Clipper()
 	{
+		blocked = false;
 		clipnodes=cliphead=NULL;
 	}
 
@@ -129,6 +131,16 @@ public:
 		SafeRemoveClipRange(AngleToPseudo(startangle), AngleToPseudo(endangle));
 	}
 
+	void SetBlocked(bool on)
+	{
+		blocked = on;
+	}
+
+	bool IsBlocked() const
+	{
+		return blocked;
+	}
+
 	bool CheckBox(const float *bspcoord);
 };
 
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index b95e1fee0..2cca5c1f0 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -763,6 +763,7 @@ void GLSectorStackPortal::DrawContents()
 	if (!(gl_drawinfo->ss_renderflags[sub - ::subsectors] & SSRF_SEEN))
 	{
 		clipper.SafeAddClipRange(0, ANGLE_MAX);
+		clipper.SetBlocked(true);
 	}
 
 	GLRenderer->DrawScene(DM_PORTAL);