Description of DeePBSP v4 Extended nodes for developers
-------------------------------------------------------

This information is intended for any port author that wishes to extend the size
of level the port can play.  It's suggested to change the standard level structures
to also have unsigned value to support large levels.  For example, change the sidedef
reference to unsigned short for the linedef struct.  Then use 0xFFFF (#define this) to
check for no sidedef and store -1 in an internal format as int for the sidedef.

Other versions can easily be made if somebody has a reason for a change that 
reflects the real world.  

CAUTION : Be sure to turn of struct alignment in the compiler, otherwise
          it may add data to the structs.

Terminology is per Intel processors.

 --- V4 Standard nodes only ---

struct Segment4
{
           int   vstart;    // from this vertex ... (allows for over 64k verts which
           int   vend;      // ... to this vertex   (can occur during node building with packed sidedefs
  unsigned short angle;     // angle (0 = east, 16384 = north, ...)
  unsigned short linedef;   // linedef that this seg goes along (allows for 64k linedefs)
           short  flip;     // true if not the same direction as linedef
  unsigned short dist;      // distance from starting point
};

--  BOTH standard V4 nodes and V4 GLNodes --

struct Pnode4
{
  short  X, Y;	           // x,y coordinates
  short  dX, dY;           // offsets
  short  bbox[2][4];       // bounding rectangles
  int    chright, chleft;  // Node or SubSector (if bit 31 is set)
};


struct SubSector4                   
{
  unsigned short segcount;    // number of Segs in this SubSector. 64k is plenty, hence no int
  int            firstseg;    // first Seg
};

 --- GL nodes only--- 

struct GLSeg4
{
  int      vstart;            // bit 31 set= GL vert
  int      vend;              // ...                
  unsigned short linedef;     // linedef that this seg goes along (allows for for 64k linedefs)
  unsigned short side;        // 0 if on right of linedef, 1 if on left 
}


--- detection the version for V4 STANDARD nodes

The NODES lump at offset 0 contains "xNd4\0\0\0\0" if V4 nodes are stored. The 0x000000 is pretty
much an impossible value in the stock node structure, so this is very reliable.

Use the above structures to decode and map the information into the ports internal format.

Please note that the information is identical to the stock node format with the 
changes only in sign and size.  

To use extended V4 nodes, the internal structure of a port should have int values for 
linedefs, sidedefs and vertices. Afer that change it becomes pretty easy to support both 
the old and new formats as well as levels with more than 32k sidedefs or vertices. 

The only major change is for sidedefs.  When a level is read, check the linedef sidedef 
reference for 0xFFFF and then store a -1 in the internal format (depends on compiler used).

Other internal formats need to be made either unsigned short (vs short) or made int.  

--- detecting the version for V4 GLNODES

Vertexs are the same format as GL version 2, however, the "magic" is different so you can tell
the format of the other lumps.  There is no need to store a "magic" number in the other lumps
and this also prevents GL2 only ports from misinterpreting.

Thus if the Nodes are V4 then at location 0 is "gNd4" vs "gNd2" in the the VERTEX lump. This
avoids the accidental confusion that can occur with V3 GL nodes that still has "gNd2" even
though the other parts are different.

The same comments apply as for STANDARD nodes.  Some ports have all the right stuff, it's just
a matter of changing a few level structures from signed to unsigned and check for 0xFFFF as a 
sidedef value and then storing -1 in the internal structure.

The old v2 "partner" value in segs is not stored in v4 since neither JDOOM, PRBOOM or VAVOOM used this 
value. Same thing goes for linedef references.  I think 64k is plenty considering that the sidedefs 
really hit the limit way before. 

The only way to get more than 64k sidedefs is to pack the sidedefs, but then the
level becomes basically uneditable.  A level like that can't be saved as is without packing it 
again. 

Vertex limit of 64k is also plenty.  The GLnodes only need int so they can distinquish the vertex type.