1.
.WAD files
Anton Gerdelan

2. making our own doom WADs
(maps/levels etc) in 1994-5
a port of DEU from http://interreality.org/~tetron/technology/lde/

3. Here is all the data!
- binary file, custom layout
- Id released specs to help modders build tools
~1994 (I went in raw though)
- IWAD and PWAD
- combines all game data
- parts of levels; { walls, floors, monsters… }
- sound effects data (proprietary format)
- music (proprietary format)
- colour palettes, images for maps, enemies,
panels…
- images with transparent bits have custom format

4. tools
- hexedit
- C
- fread()
- fwrite()
- fseek()
- valgrind
- Audacity
- OpenGL
- DosBox

5. binary sleuthing
- figure out file structure
- search for strings
- determine directory
structure
- match hex-format
address with values
- h/w arch of 1993
machines
- trial and error
e.g. directory started at
~ 00 BC C5 00
this 4-byte group says
“C4 C5 BC 00”

6. printf() the directory
- Directory entries in block at
end of file:
- entry string (good hint)
- entry size in bytes
- entry offset from file start -
use fseek()
- I was after the music but
couldn’t resist
- “VERTEX” “LINEDEF”
“SECTOR” …

7. LINEDEF ~walls
references 2 VERTEXES
references 1-2 SIDEDEFS
find height in SECTORS
VERTEX
has 2 (x,y) integer values
SECTOR
~floor/ceiling
bounded by SIDEDEFS
not tessellated
not always convex
have holes

8. Walls and Floors
- Create a struct for each type of map part and
put them in arrays to do quick line->height etc.
- Walls - just extrude them up?
- lower lip
- mid (sometimes a gap)
- upper lip
- Floors - tessellation algorithm
- I used “Ear Clipping”
extended for holes

9. Ear-Clipping Tessellation
- David Eberly’s white paper is great
https://www.geometrictools.com/
Documentation/
TriangulationByEarClipping.pdf
- breaks a simple polygon into triangles
- single region bounded by loop of edges
and verts
- a group of 3 consecutive verts is reflex
(angle > pi) or convex (angle < pi)
- convex triplet = a polygon ear
- but not if another vert is inside that triangle
- and final line is fully inside poly
- can recurse clipping until 3 vertices remain
O(n^3) … but can improve on this
The Two Ears Theorem
A polygon of >3 sides always has at
least 2 valid ears.
is_convex(
vert a, vert b, vert c );
is_in_triangle(
vert a, vert b, vert c,
vert x );

10. Ear-Clipping Tessellation
- Loop around all n verts in polygon
- use curr-1, curr, curr+1 (modulo n)
- test all other verts - is_in_triangle()
(pre-calc current reflex/convex status per triangle
to reduce time complexity). ~O(n^2)
- if (is_ear) {
- remove curr vertex from polygon
- add triangle to a list
- decrement n.
- if n == 3 found last triangle. HALT
- https://youtu.be/9wrhIvpOKlg
shows algorithm on Doom E1M1 in steps
- src (experiment 039)
https://github.com/capnramses/opengl_expmts

11. - extend Ear Clipping for O-shapes (hole in middle):
- outer vertices clockwise order - make inner loop CCW
- add to end of loop’s vertex list
- add a valid “cut” line between outer and inner (tricky)
- proceed as normal - now treated as a C-shape
Pool of toxic sludge inside
another sector - gets obscured

12. modified ear clipping
worked!
(sludge pool no longer
paved over)

13. shader for ceilings with “sky” image
texture is one half of a 180
that wraps ~ proto-skybox
mapped to 320x200 screen
pixels so hard to map to
arbitrary size/resolution

14. Secrets of Romero’s Head
- found tiny ledges on wall
that had big daemon head
- clever way of splitting
enormous image into many
sub-images

15. Hacking the unpublished
sound format
- Custom 8-byte header - I just ditched it
- Body is a blob of waveform data
- Guess format based on original
SoundBlaster
- Trial and error in Audacity raw data import
- unsigned 8-bit mono 11025Hz samples
- 16 bytes additional padding at front and end that can all be
trimmed, leaving raw sound data.
- Seems to work. https://youtu.be/AZxU9fNsWoU

16. Music format
- Wasn’t MIDI! It was MIDI encoded into a proprietary format
- 9 instruments
- custom playback software (never released)
- MIDI2MUS and MUS2MIDI (MS-DOS)
- I don’t know enough about MIDI etc to work it out.
- I used DosBox and an ancient MUS2MIDI
- Sub-par results - need original playback software!

17. “Dude, you need to stop
working on your vanity projects!”
- How do other Doom renderers deal with the sector tessellation
problem?
- They didn’t! Specially prepared .WAD [cheating!].
- Better potential solution
- try Delaunay triangulation instead
- Source code
- DeWad - https://github.com/capnramses/doom_projects
- OpenGL renderer - Blog post about it - antongerdelan.net/blog/

18. Finding a good cut
- find rightmost inner loop vertex
- project vector right from it
- intersect all outer edges
- find closest vertex to projected
line (except if vertex is not visible
to first vertex).
- if closest point is an outer point
use this. HALT.
- otherwise search the outer edge
for valid visible vertex to first
(many tests and conditions here)
multiple holes or complex?
create hierarchies of simple
shapes, solve small, combine