diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 79f40ae5c9..40aa5ae374 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1279,6 +1279,7 @@ set (PCH_SOURCES
 	p_3dfloors.cpp
 	p_3dmidtex.cpp
 	p_acs.cpp
+	p_actionfunctions.cpp
 	p_buildmap.cpp
 	p_ceiling.cpp
 	p_conversation.cpp
@@ -1417,7 +1418,6 @@ set (PCH_SOURCES
 	textures/warptexture.cpp
 	thingdef/olddecorations.cpp
 	thingdef/thingdef.cpp
-	thingdef/thingdef_codeptr.cpp
 	thingdef/thingdef_data.cpp
 	thingdef/thingdef_exp.cpp
 	thingdef/thingdef_expression.cpp
diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/p_actionfunctions.cpp
similarity index 100%
rename from src/thingdef/thingdef_codeptr.cpp
rename to src/p_actionfunctions.cpp
diff --git a/src/r_plane.cpp b/src/r_plane.cpp
index cfc30e1c7b..c4d72b1a09 100644
--- a/src/r_plane.cpp
+++ b/src/r_plane.cpp
@@ -852,10 +852,11 @@ extern FTexture *rw_pic;
 // since the most anyone can ever see of the sky is 500 pixels.
 // We need 4 skybufs because wallscan can draw up to 4 columns at a time.
 // Need two versions - one for true color and one for palette
+#define MAXSKYBUF 3072
 static BYTE skybuf[4][512];
-static uint32_t skybuf_bgra[4][512];
+static uint32_t skybuf_bgra[MAXSKYBUF][512];
 static DWORD lastskycol[4];
-static DWORD lastskycol_bgra[4];
+static DWORD lastskycol_bgra[MAXSKYBUF];
 static int skycolplace;
 static int skycolplace_bgra;
 
@@ -888,9 +889,19 @@ static const BYTE *R_GetOneSkyColumn (FTexture *fronttex, int x)
 // Get a column of sky when there are two overlapping sky textures
 static const BYTE *R_GetTwoSkyColumns (FTexture *fronttex, int x)
 {
-	DWORD ang = (skyangle + xtoviewangle[x]) ^ skyflip;
-	DWORD angle1 = (DWORD)((UMulScale16(ang, frontcyl) + frontpos) >> FRACBITS);
-	DWORD angle2 = (DWORD)((UMulScale16(ang, backcyl) + backpos) >> FRACBITS);
+	DWORD ang, angle1, angle2;
+
+	if (r_linearsky)
+	{
+		angle_t xangle = (angle_t)((0.5 - x / (double)viewwidth) * FocalTangent * ANGLE_90);
+		ang = (skyangle + xangle) ^ skyflip;
+	}
+	else
+	{
+		ang = (skyangle + xtoviewangle[x]) ^ skyflip;
+	}
+	angle1 = (DWORD)((UMulScale16(ang, frontcyl) + frontpos) >> FRACBITS);
+	angle2 = (DWORD)((UMulScale16(ang, backcyl) + backpos) >> FRACBITS);
 
 	// Check if this column has already been built. If so, there's
 	// no reason to waste time building it again.
@@ -935,17 +946,18 @@ static const BYTE *R_GetTwoSkyColumns (FTexture *fronttex, int x)
 	else
 	{
 		//return R_GetOneSkyColumn(fronttex, x);
-		for (i = 0; i < 4; ++i)
+		for (i = skycolplace_bgra - 4; i < skycolplace_bgra; ++i)
 		{
-			if (lastskycol_bgra[i] == skycol)
+			int ic = (i % MAXSKYBUF); // i "checker" - can wrap around the ends of the array
+			if (lastskycol_bgra[ic] == skycol)
 			{
-				return (BYTE*)(skybuf_bgra[i]);
+				return (BYTE*)(skybuf_bgra[ic]);
 			}
 		}
 
 		lastskycol_bgra[skycolplace_bgra] = skycol;
 		uint32_t *composite = skybuf_bgra[skycolplace_bgra];
-		skycolplace_bgra = (skycolplace_bgra + 1) & 3;
+		skycolplace_bgra = (skycolplace_bgra + 1) % MAXSKYBUF;
 
 		// The ordering of the following code has been tuned to allow VC++ to optimize
 		// it well. In particular, this arrangement lets it keep count in a register