Fix btsx e2 map 20

prboom2/src/p_maputl.c

@@ -378,7 +378,9 @@ dboolean P_BlockLinesIterator(int x, int y, dboolean func(line_t*))
   // Most demos go out of sync, and maybe other problems happen, if we
   // don't consider linedef 0. For safety this should be qualified.
 
-  if (!demo_compatibility) // killough 2/22/98: demo_compatibility check
+  // killough 2/22/98: demo_compatibility check
+  // In mbf21, skip if all blocklists start w/ 0 (fixes btsx e2 map 20)
+  if ((!demo_compatibility && !mbf21) || (mbf21 && skipblstart))
     list++;     // skip 0 starting delimiter                      // phares
   for ( ; *list != -1 ; list++)                                   // phares
     {

prboom2/src/p_setup.c

@@ -164,6 +164,8 @@ mobj_t    **blocklinks;           // for thing chains
 int blockmapxneg = -257;
 int blockmapyneg = -257;
 
+dboolean skipblstart;  // MaxW: Skip initial blocklist short
+
 //
 // REJECT
 // For fast sight rejection.
@@ -2015,6 +2017,8 @@ static dboolean P_VerifyBlockMap(int count)
   int x, y;
   int *maxoffs = blockmaplump + count;
 
+  skipblstart = true;
+
   for(y = 0; y < bmapheight; y++)
   {
     for(x = 0; x < bmapwidth; x++)
@@ -2044,6 +2048,9 @@ static dboolean P_VerifyBlockMap(int count)
 
       list   = blockmaplump + offset;
 
+      if (*list != 0)
+        skipblstart = false;
+
       // scan forward for a -1 terminator before maxoffs
       for(tmplist = list; ; tmplist++)
       {

prboom2/src/p_setup.h

@@ -54,6 +54,8 @@ extern fixed_t  bmaporgx;
 extern fixed_t  bmaporgy;        /* origin of block map */
 extern mobj_t   **blocklinks;    /* for thing chains */
 
+extern dboolean skipblstart; // MaxW: Skip initial blocklist short
+
 // MAES: extensions to support 512x512 blockmaps.
 extern int blockmapxneg;
 extern int blockmapyneg;