![“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/](https://image.slidesharecdn.com/wadfiles-170609091856/85/Cracking-into-Doom-1993-WAD-Files-17-320.jpg)
Cracking into Doom (1993) WAD Files
- 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