From 7b8a564f69688515319ccd425f2b88ffe8b7b120 Mon Sep 17 00:00:00 2001
From: James R <justsomejames2@gmail.com>
Date: Wed, 5 Apr 2023 00:13:18 -0700
Subject: [PATCH] Cull BSP behind a raised floor or lowered ceiling that covers
 the entire screen

This can effectively award the performance of a thok
barrier automatically, for walls that completely fill the
screen vertically. (Not pegged midtextures.)
---
 src/r_bsp.cpp | 33 +++++++++++++++++++++++++++++----
 src/r_bsp.h   |  1 +
 src/r_segs.c  | 25 ++++++++++++++-----------
 3 files changed, 44 insertions(+), 15 deletions(-)

diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index 84987a32d..ddafbb014 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -43,6 +43,10 @@ drawseg_t *ds_p = NULL;
 // indicates doors closed wrt automap bugfix:
 INT32 doorclosed;
 
+// A wall was drawn covering the whole screen, which means we
+// can block off the BSP across that seg.
+boolean g_walloffscreen;
+
 boolean R_NoEncore(sector_t *sector, levelflat_t *flat, boolean ceiling)
 {
 	const boolean invertEncore = (sector->flags & MSF_INVERTENCORE);
@@ -99,6 +103,7 @@ enum class ClipType
 	//  e.g. single sided LineDefs (middle texture)
 	//  that entirely block the view.
 	kSolid,
+	kSolidDontRender,
 
 	// Clips the given range of columns, but does not include it in the clip list.
 	// Does handle windows, e.g. LineDefs with upper and lower texture.
@@ -138,7 +143,10 @@ void R_ClipWallSegment(INT32 first, INT32 last)
 		if (last < start->first - 1)
 		{
 			// Post is entirely visible (above start), so insert a new clippost.
-			R_StoreWallRange(first, last);
+			if constexpr (Type != ClipType::kSolidDontRender)
+			{
+				R_StoreWallRange(first, last);
+			}
 
 			if constexpr (Type != ClipType::kPass)
 			{
@@ -161,7 +169,10 @@ void R_ClipWallSegment(INT32 first, INT32 last)
 		}
 
 		// There is a fragment above *start.
-		R_StoreWallRange(first, start->first - 1);
+		if constexpr (Type != ClipType::kSolidDontRender)
+		{
+			R_StoreWallRange(first, start->first - 1);
+		}
 
 		if constexpr (Type != ClipType::kPass)
 		{
@@ -178,7 +189,11 @@ void R_ClipWallSegment(INT32 first, INT32 last)
 	while (last >= (next+1)->first - 1)
 	{
 		// There is a fragment between two posts.
-		R_StoreWallRange(start->last + 1, (start+1)->first - 1);
+		if constexpr (Type != ClipType::kSolidDontRender)
+		{
+			R_StoreWallRange(next->last + 1, (next+1)->first - 1);
+		}
+
 		next++;
 
 		if (last <= next->last)
@@ -196,7 +211,10 @@ void R_ClipWallSegment(INT32 first, INT32 last)
 	}
 
 	// There is a fragment after *next.
-	R_StoreWallRange(start->last + 1, last);
+	if constexpr (Type != ClipType::kSolidDontRender)
+	{
+		R_StoreWallRange(next->last + 1, last);
+	}
 
 	if constexpr (Type != ClipType::kPass)
 	{
@@ -629,10 +647,17 @@ static void R_AddLine(seg_t *line)
 		return;
 
 clippass:
+	g_walloffscreen = false;
 	R_ClipWallSegment<ClipType::kPass>(x1, x2 - 1);
+
+	if (g_walloffscreen)
+	{
+		R_ClipWallSegment<ClipType::kSolidDontRender>(x1, x2 -1);
+	}
 	return;
 
 clipsolid:
+	g_walloffscreen = false;
 	R_ClipWallSegment<ClipType::kSolid>(x1, x2 - 1);
 }
 
diff --git a/src/r_bsp.h b/src/r_bsp.h
index 66d1ff9cc..d01fa97f0 100644
--- a/src/r_bsp.h
+++ b/src/r_bsp.h
@@ -39,6 +39,7 @@ extern drawseg_t *curdrawsegs;
 extern drawseg_t *drawsegs;
 extern drawseg_t *ds_p;
 extern INT32 doorclosed;
+extern boolean g_walloffscreen;
 
 // BSP?
 void R_ClearClipSegs(void);
diff --git a/src/r_segs.c b/src/r_segs.c
index 2b6f471d6..74800fb21 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -2737,23 +2737,26 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 
 		if (toptexture)
 		{
-			pixhigh = (centeryfrac>>4) - FixedMul (worldhigh, rw_scale);
-			pixhighstep = -FixedMul (rw_scalestep,worldhigh);
+			fixed_t topfracend = (centeryfrac>>4) - FixedMul (worldhighslope, ds_p->scale2);
 
-			if (backsector->c_slope) {
-				fixed_t topfracend = (centeryfrac>>4) - FixedMul (worldhighslope, ds_p->scale2);
-				pixhighstep = (topfracend-pixhigh)/(range);
-			}
+			pixhigh = (centeryfrac>>4) - FixedMul (worldhigh, rw_scale);
+			pixhighstep = (topfracend-pixhigh)/(range);
+
+			// If the lowest part of a ceiling stretching down covers the entire screen
+			if (min(pixhigh, topfracend)>>HEIGHTBITS >= viewheight-1)
+				g_walloffscreen = true;
 		}
 
 		if (bottomtexture)
 		{
+			fixed_t bottomfracend = (centeryfrac>>4) - FixedMul (worldlowslope, ds_p->scale2);
+
 			pixlow = (centeryfrac>>4) - FixedMul (worldlow, rw_scale);
-			pixlowstep = -FixedMul (rw_scalestep,worldlow);
-			if (backsector->f_slope) {
-				fixed_t bottomfracend = (centeryfrac>>4) - FixedMul (worldlowslope, ds_p->scale2);
-				pixlowstep = (bottomfracend-pixlow)/(range);
-			}
+			pixlowstep = (bottomfracend-pixlow)/(range);
+
+			// If the highest part of a floor stretching up covers the entire screen
+			if ((max(pixlow, bottomfracend)+HEIGHTUNIT-1)>>HEIGHTBITS <= 0)
+				g_walloffscreen = true;
 		}
 
 		{