code:

---

# bytes name            description
------- --------------- --------------------------------------------
4       x1              unknown (version ?)
4       w               width of map - 1
4       h               height of map - 1
(4)     act             act of the map, from 0 to 4
(4)     x2              unknown
4       num_files       number of dt1 / tg1 files (unused)
?                       num_files string (unused)
(4)     num_wall        number of wall's layers 
(4)     num_floor       number of floor's layers

---

If x1 = 3, there is NO act data in the header (skip it).

If x1 = 3 or 8, these datas are NOT present in the file (skip them) :
      * x2
      * num_wall
      * num_floor

As a general rule, only read ds1 which have x1 different of 3 and 8.
The format when it is 3 or 8 cause problems. It still need to be learn.

Now follow a variable amount of layers.
Each layers have (w+1) * (h+1) cells.
Each cell is 4 bytes.
There are 2 layers by wall in the file !

To compute the total number of layers *in the file* :
      if x2 not equal 0
            maxlayer = x2 + (num_wall * 2) + num_floor;
      else
            maxlayer = 1 + x2 + (num_wall * 2) + num_floor;

(but follow this :
      if x1 = 3 or 8 or 12 then maxlayer = 6
      if x1 = 13 then maxlayer = 7
)

The ds1 format is not really well-known as you see

The cells are in the common way of reading : left to right, then up to down.

First come num_wall * 2 layers, for walls
Then come num_floor layers, for floors
Then come the unknown rest (maxlayer - x3*2 - x4)

After this layers, 4 bytes for number_objects. Each objects in the map is 5 datas
of 4 bytes each. The 5th seems to always be zero. The 1st is either 1 or 2.

After, come the paths infos.
First 4 bytes for npc_path.
then npc_path datas, structured like :
      4 bytes for some_number
      4 bytes for ?
      4 bytes for ?
      then some_number datas structured like :
            4 bytes for ?
            4 bytes for ?
            4 bytes for ?

I never took the time to understand the objetcs or the paths infos (as you see).

Now, some ds1 / dt1 relations.
==============================
Islveo's ds1 editor named each 4 bytes of a cell prop1 to prop4.

First, let's draw all the floor layers (num_floor layers)
---------------------------------------------------------
if the prop1 of the cell is not 0
draw the tile with :
orientation = 0
sub_index = prop2
main_index = (prop3 / 16) + ((prop4 & 0x0F) * 16)

The main_index of the dt1 is split in 2 in the ds1.
A nibble is 4 bits, half of a byte.
The low nibble of main_index in dt1 is high nibble of prop3 in ds1.
The high nibble of main_index in dt1 is low nibble of prop4 in ds1.
(hence the precedent main_index formula)

Now let's draw walls (num_wall layers)
--------------------------------------
There are 2 layers in the file for each layer of walls.
The 2nd is for the orientation of the dt1
the 1st is for the rest