Structure of a dt1 :
--------------------

code:

---

* file header
* X block headers
* X sub-block struct, each one structured like that :
      - Y sub-blocks header
      - Y sub-blocks data

---

Concepts:
---------
A block is a tile (160 pixels width max, variable height)
A tile can be understand as a floor with / without wall
The game use 3d-isometric tiles
A tile is composed of many sub-tiles
      * Floor have 5*5 (25) sub-tiles (or less)
            - Sub-tiles are in 3d-isometric shape
      * Walls have variable amount of sub-tiles
            - Each sub-tiles fit in a 32*32 pixels box
Roof exists : they are floors *above* regular floors
        (important for player/tile drawing priority)

FILE HEADER
===========

code:

---

# bytes name            description
------- --------------- --------------------------------------------
4       x1              version (= 7)
4       x2              version (= 6)
260     zeros1          unused
4       nb_block        # of blocks
4       bh_ptr          pointer in file to block headers (= 0x114)

---

There are some dt1 with x1 and x2 not equal to 7 and 6. They are in
another format, or maybe just in a variation of this format, which
is not yet known.

BLOCK HEADER
============

code:

---

# bytes name            description
------- --------------- ---------------------------------------------------------
4       direction       direction
2       roof_y          # of pixels to the up when drawing the block
1       sound           sound index when walking / runing
1       animated        set to 0x01 when floor is animated
4       size_y          power of 32 pixels
4       size_x          power of 32 pixels
4       zeros1          unused
4       orientation     orientation (islveo's corner prop 1)
4       main_index      main index
4       sub_index       sub-index
4       frame           if floor animated, # of frame else ?
1       unknown_a       ?
1       unknown_b       ?
1       unknown_c       ?
1       unknown_d       ?
25      floor_flags     for each sub-tiles from right to left, then bottom to up
7       zeros2          unused
4       data_ptr        pointer to sub-block headers
4       length          length of the sub-blocks
12      zeros3          unused

---

What identified a dt1 in the ds1 (d2's map) is a not a simple index, it's a
combination of orientation / main_index / sub_index. There can be more than
1 tile with this combination in the dt1. In this case, the game choose 1
randomly whithin the same.

direction seems to be a "general orientation", and orientation some kind
of a part of this one. When direction is 3, there IS always 2 kind of tiles,
1 with orientation = 3, and another with 4. These 3 and 4 must be draw at
the same place, they are the left and right part of a corner.

roof_y tells in how many pixels the tile must be draw upper.

size_y and size_x are the "box" where the tile can fit in. Relative to the
bottom-left coener of the bitmap.

if floor is animated, frame is the number of frame in the animation. But it
is also used in other case... I think this is some kind of "rarity" for the
tiles with the same orientation / main_index / sub_index.

floor_flags are for each sub-tiles of the floor, even if there is only a
wall to draw. It is used to know if the player can go thru the sub-tile, but
maybe for some kind of transparency too.

Floors and roof (orientation = 0 and 15) need to be draw 80 pixels lower than
the walls.

SUB-BLOCK HEADER
================

code:

---

# bytes name            description
------- --------------- ---------------------------------------------------------
2       x_pos           x offset where to raw the sub-tile
2       y_pos           y offset where to draw the sub-tile
2       zeros1          unused
1       grid_x          if sub-tile of floor, its x position in the floor
1       grid_y          if sub-tile of floor, its y position in the floor
2       tile_format     method of drawing the sub-tile
4       sub-length      length of the sub-block data
2       zeros2          unused
4       data_offset     pointer FROM SUB-BLOCK HEADER of this datas

---

if tile_format = 0x0001 it is a 3d-isometric sub-tile, else regular one

sample of code for drawing 3d-isometric sub-tile (in C language)

code:

---

void draw_sub_tile_isometric (BITMAP * dst, int x0, int y0, const UBYTE * data, int length)
{
   UBYTE * ptr = data;
   int   x, y=0, n,
         xjump[15] = {14, 12, 10, 8, 6, 4, 2, 0, 2, 4, 6, 8, 10, 12, 14},
         nbpix[15] = {4, 8, 12, 16, 20, 24, 28, 32, 28, 24, 20, 16, 12, 8, 4};
   // 3d-isometric subtile is 256 bytes, no more, no less
   if (length != 256)
      return;
   // draw
   while (length > 0)
   {
      x = xjump[y];
      n = nbpix[y];
      length -= n;
      while (n)
      {
         putpixel(dst, x0+x, y0+y, * ptr);
         ptr++;
         x++;
         n--;
      }
      y++;
   }
}

---

sample of code for drawing normal sub-tile (in C language)

code:

---

void draw_sub_tile_normal (BITMAP * dst, int x0, int y0, const UBYTE * data, int length)
{
   UBYTE * ptr = data, b1, b2;
   int   x=0, y=0;
   // draw
   while (length > 0)
   {
      b1 = * ptr;
      b2 = * (ptr + 1);
      ptr += 2;
      length -= 2;
      if (b1 || b2)
      {
         x += b1;
         length -= b2;
         while (b2)
         {
            putpixel(dst, x0+x, y0+y, * ptr);
            ptr++;
            x++;
            b2--;
         }
      }
      else
      {
         x = 0;
         y++;
      }
   }
}

---