From 467ec719d18d311777d592c27cb0b2bef5c1f409 Mon Sep 17 00:00:00 2001
From: Fabian Greffrath <fabian@greffrath.com>
Date: Fri, 1 Mar 2024 14:24:00 +0100
Subject: [PATCH] render linedef texture instead of sky if flat is missing
 (#1543)

Fixes #1540
---
 src/r_data.c  | 12 ++++++++----
 src/r_defs.h  |  2 ++
 src/r_plane.c |  3 +++
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/r_data.c b/src/r_data.c
index 0d82d235..56f369b7 100644
--- a/src/r_data.c
+++ b/src/r_data.c
@@ -1048,11 +1048,10 @@ void R_InitData(void)
 int R_FlatNumForName(const char *name)    // killough -- const added
 {
   int i = (W_CheckNumForName)(name, ns_flats);
-  if (i == -1)
+  if (i == NO_TEXTURE)
   {
-    // [FG] render missing flats as SKY
     I_Printf(VB_WARNING, "R_FlatNumForName: %.8s not found", name);
-    return skyflatnum;
+    return i;
   }
   return i - firstflat;
 }
@@ -1124,7 +1123,12 @@ void R_PrecacheLevel(void)
   memset(hitlist, 0, numflats);
 
   for (i = numsectors; --i >= 0; )
-    hitlist[sectors[i].floorpic] = hitlist[sectors[i].ceilingpic] = 1;
+  {
+    if (sectors[i].floorpic > NO_TEXTURE)
+        hitlist[sectors[i].floorpic] = 1;
+    if (sectors[i].ceilingpic > NO_TEXTURE)
+        hitlist[sectors[i].ceilingpic] = 1;
+  }
 
   for (i = numflats; --i >= 0; )
     if (hitlist[i])
diff --git a/src/r_defs.h b/src/r_defs.h
index 9906c52f..86339cf5 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -41,6 +41,8 @@ struct mobj_s;
 
 #define MAXDRAWSEGS   256
 
+#define NO_TEXTURE (-1)
+
 //
 // INTERNAL MAP TYPES
 //  used by play and refresh
diff --git a/src/r_plane.c b/src/r_plane.c
index aabfacb7..37cd1fe6 100644
--- a/src/r_plane.c
+++ b/src/r_plane.c
@@ -304,6 +304,9 @@ visplane_t *R_FindPlane(fixed_t height, int picnum, int lightlevel,
   visplane_t *check;
   unsigned hash;                      // killough
 
+  if (picnum == NO_TEXTURE)
+    return NULL;
+
   if (picnum == skyflatnum || picnum & PL_SKYFLAT)  // killough 10/98
   {
     lightlevel = 0;   // killough 7/19/98: most skies map together