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GTHTML Documentation

Based on reverse-engineering all 36 pages in MENU/MENU_HTM.ARC (PAL-era disc layout). This is not HTML; it is a compact binary menu page / hotspot script used by the GT1 front-end.

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1. Role in the game

GTHTML files describe one menu screen:

• Which background TIM to draw
• Clickable regions (rectangles) and what they do
• Links to other pages (.HTM) or engine actions (LIST_GARAGE, SHOW_SPEC, …)

They live in MENU/MENU_HTM.ARC, named by MENU/HTMLS.IDX. Backgrounds come from MENU/MENU_IMG.ARC / IMAGES.IDX (e.g. home.htm → HOME.tim).

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2. File layout (overview)

Offset  Size   Description
──────  ─────  ───────────────────────────────────────────
0x00    12     Magic: "@(#)GTHTML\0\0"
0x0C     4     Padding / reserved (always 00 00 00 00 in MENU_HTM)
0x10    …      Body (commands)
EOF-3    3     End marker: AF 8D 00

Total size is typically 60–350 bytes. No embedded images or text paragraphs—only structure and names.

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3. Header

40 28 23 29 47 54 48 54 4D 4C 00 00   ; "@(#)GTHTML\0\0"
00 00 00 00                           ; reserved

Detection: data.startswith(b"@(#)GTHTML").

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4. Body command stream

Body starts at offset 0x10. It is a sequence of records. Known records:

4.1 Page background (0x0D 0x02) — always first

0D 02
<u8 len> <len bytes ASCII TIM name>
2F                                      ; '/'
<u8 len> <len bytes ASCII mode>         ; always "bgmap" in MENU_HTM

Example (home.htm):

0D 02 08 48 4F 4D 45 2E 74 69 6D 2F 05 62 67 6D 61 70
        |  H  O  M  E  .  t  i  m  /  |  b  g  m  a  p

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4.2 Hotspot — type 1 (0x05 0x01)

Rectangular click target in screen coordinates.

05 01
04          ; parameter count (always 4 for x0,y0,x1,y1)
00          ; padding / flags (always 00 here)
<u16 le x0> <u16 le y0> <u16 le x1> <u16 le y1>
<u8 len> <len bytes ASCII target>

Coordinates: corners of a box in PS1 display space (origin top-left; full screen often 640×480, e.g. title page uses (0,0)–(640,480) = 00 00 00 00 80 02 E0 01).

Example (home.htm → Garage):

05 01 04 00 A4 00 FC 00 08 01 60 01 0A 47 41 52 41 47 45 2E 48 54 4D
              x0=164 y0=252 x1=264 y1=352     | GARAGE.HTM

Target string is either:

Names are ASCII, length-prefixed (max practical length ≤ 64). Case is as stored (MAP.HTM, HOME.tim).

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4.3 Widget / compact control — type 2 (0x05 0x02)

Smaller control, often sidebar / icon-style navigation (exact engine semantics partly inferred).

05 02
03          ; parameter count (always 3 in MENU_HTM)
00          ; padding
<u16 le a> <u16 le b> <u16 le c>
<u8 len> <len bytes ASCII target>

Example (many pages — “back” control toward parent):

05 02 03 00 30 00 64 00 19 00 07 48 4F 4D 45 2E 48 54 4D
              48     100    25       HOME.HTM

Same target string rules as hotspots. Common on pages that share the left Map / Home chrome.

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4.4 End marker

AF 8D 00

Always present at end of MENU_HTM pages. Treat as EOF for the command stream.

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5. String encoding

All names use the same scheme:

<u8 length N> <N bytes ASCII>

• No null terminator inside the string
• Characters are printable ASCII (letters, digits, ., _, -)
• TIM names often end in .tim; pages in .HTM
• Actions have no extension (LIST_PARTS, REPLAY_DEMO)

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6. Coordinate system

• u16 little-endian
• Screen space roughly 0…640 × 0…480 (NTSC/PAL menu rendering)
• Hotspot type 1: axis-aligned box (x0,y0)–(x1,y1)
• Type 2: point-like / compact hit area, not a full box in the file

Overlays for tools should draw type-1 rects; type-2 can be shown as a marker at (a,b) with radius from c or a fixed pad.

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7. Semantic target catalogue (MENU_HTM)

Page links (subset)

HOME.HTM, MAP.HTM, GTF.HTM, GARAGE.HTM, TOYOTA.HTM, TRD.HTM, GAMEMODE.HTM, GTF-CHAMP.HTM, GTF-LICENCE.HTM, GTF-SPECIAL.HTM, TOYOTA-NEW.HTM, TOYOTA-USED.HTM, TRD-*.HTM, …

Engine actions (subset)

Rule of thumb: if the target contains .HTM, it is a page; otherwise it is an action id.

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8. Full page example (title.htm, 63 bytes)

0000  40 28 23 29 47 54 48 54 4D 4C 00 00   @(#)GTHTML\0\0
000C  00 00 00 00                           reserved
0010  0D 02                                 background cmd
0012  09 "TITLE.tim" 2F 05 "bgmap"          TIM + mode
0022  05 01 04 00
      00 00  00 00  80 02  E0 01            rect (0,0)-(640,480)
      0C "GAMEMODE.HTM"                     entire screen → gamemode
003D  AF 8D 00                              end

Meaning: show TITLE.tim; any click goes to GAMEMODE.HTM.

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9. Full page example (home.htm)

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10. Relationship to other MENU files

MENU/
  HTMLS.IDX      ← ordered list of .htm names (36 lines)
  MENU_HTM.ARC   ← GTHTML binaries in that order
  IMAGES.IDX     ← ordered list of .tim names (40 lines)
  MENU_IMG.ARC   ← TIM binaries in that order
  MENU_SND.ARC   ← sounds (separate)

• GTHTML does not store image pixels; it only stores the TIM file name.
• Loader resolves HOME.tim via IDX / archive binding.
• Root disc MENU_IMG.ARC (large, 6 language packs) is a different asset set; the small MENU/MENU_IMG.ARC is what these pages use.

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11. Editing implications

Safe, high-value edits:

1. Retarget — change length-prefixed string (same length, or rewrite record and shift tail).
2. Swap background TIM name — same length easiest (HOME.tim → other 8-char name); longer names require memmove of the body.
3. Move hotspot — rewrite the four u16 values; keep 05 01 04 00 prefix.

Harder:

• Insert/delete records (must fix stream and file size; ARC in-place slot may not fit if larger).
• New pages (need new ARC entry + IDX line + matching TIM).

Preserve:

• Magic + 4 zero bytes
• Leading 0D 02 background block
• Trailing AF 8D 00
• 05 01 / 05 02 layouts unless the engine is fully re-verified

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12. Unknown / open questions

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13. Minimal parser pseudocode

assert data[0:12] == "@(#)GTHTML\0\0"
i = 16
assert data[i:i+2] == 0x0D 0x02; i += 2
tim = read_pascal_string(data, i); i = after
assert data[i] == '/'; i += 1
mode = read_pascal_string(data, i); i = after

while i < len:
  if data[i:i+3] == AF 8D 00: break
  if data[i] == 0x05 and data[i+1] == 0x01:
    i += 2
    assert data[i] == 4; i += 1
    assert data[i] == 0; i += 1
    x0,y0,x1,y1 = u16le×4; i += 8
    target = read_pascal_string(data, i); i = after
    emit HOTSPOT(rect, target)
  elif data[i] == 0x05 and data[i+1] == 0x02:
    i += 2
    assert data[i] == 3; i += 1
    assert data[i] == 0; i += 1
    a,b,c = u16le×3; i += 6
    target = read_pascal_string(data, i); i = after
    emit WIDGET(a,b,c, target)
  else:
    error unknown opcode

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14. Summary

GTHTML is a tiny hotspot script:

1. Header magic
2. Background TIM + bgmap
3. List of hotspots (rect + target) and widgets (compact control + target)
4. End marker AF 8D 00

Targets are either other menu pages or hard-coded game actions. For tooling, parsing to {background, hotspots[], widgets[]} is enough for preview, navigation graph, link retargeting, and TIM pairing—without treating the file as real HTML.

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Document generated from MENU/MENU_HTM.ARC analysis (36 pages).

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