PC-98 format

This document describes the format of data in Prince of Persia 1 for the PC-98.

General

Byte order: Numbers larger than a byte use little-endian (Intel) byte order, unless noted otherwise.

Number systems: Hexadecimal numbers are prefixed with 0x. This is omitted in sequences of bytes, for readability.

Numbering of bits: The least significant bit of a byte is bit 0, the most significant bit of a byte is bit 7.

Tools: A Japanese programmer, Zarazala, has made some tools for working with the files described in this document. You can get them from #External links. In each section below, I mention the relevant tool.

Disk images

Disk images can be either headerless (*.TFD), or have a header (*.FDI). Emulators can use both.

Online, this game is most commonly found in *.FDI files, these have a header of 0x1000 bytes.

• Tools: datacut.exe to extract files from a (headerless!) disk image, makeimg.exe to make a disk image from files.

How recognize and convert headered images

A headerless game disk starts with the bytes EB 0A. If they appear at offset 0x1000 then you have a headered disk image.

To convert a headered disk image to headerless, go to offset 0x1000 and delete everything before it. You might want to save the new file under a different name.

FDI header

The FDI header contains the following information:

Offset in bytes	Size	Value on PoP disks	Meaning
0x00	4 bytes	0	(unknown)
0x04	4 bytes	0x90 = 144	(unknown)
0x08	4 bytes	0x1000 = 4096	Start offset of the raw disk image (i.e. the size of the FDI header).
0x0C	4 bytes	0x134000 = 1261568	Size of the raw disk image in bytes.
0x10	4 bytes	0x400 = 1024	Size of a sector (or cluster?) in bytes.
0x14	4 bytes	8	Number of sectors per track?
0x18	4 bytes	2	Number of sides?
0x1C	4 bytes	0x4D = 77	Number of tracks per side?

If you multiply the last four numbers, you get the size of the raw disk image: 0x400 * 8 * 2 * 0x4D = 0x134000.

The rest of the header is filled with zeroes.

File system

A disk consists of 0x4D0 sectors, numbered from 0 to 0x4CF. Each sector is 0x400 = 1024 bytes.

The game disk (disk A) contains the following parts:

Offset in bytes	Occupied sectors	Contents
0x0000 - 0x03FF	0	#Boot sector
0x0400 - 0x0FFF	1 - 3	#File allocation table
0x1000 - 0x1FFF	4 - 7	#Directory
0x2000 - 0x133FFF	8 - 0x4CF	Data area

The offsets in the table assume you have a headerless disk image.

Boot sector

The boot sector contains the code for starting the game.

From offset 2 is the disk label "GAME DISK" on disk A, and "USER DISK" on disk B.

Directory

This area contains 0x100 = 256 entries, of 0x10 = 16 bytes each.

Each entry describes a file in the following format:

Offset in bytes	Size	Meaning
0	8 bytes	Base name. If it's shorter than 8 characters then it's padded with spaces (0x20).
8	3 bytes	Extension. (The same padding is used here, although it does not occur in the original PoP disk image.)
0x0B = 11	3 bytes	Unknown. Might be file attributes and/or modification date/time?
0x0E = 14	2 bytes	The number of the first sector of this file.

To get the full file name, concatenate the base name (with padding removed), a dot, and the extension.

Unused entries are filled with 0xFF bytes.

File allocation table

This area contains 2-byte entries for each sector on the disk.

There is space for 0x600 entries, but only the first 0x4D0 entries are used, since the disk has only that many sectors. The unused entries are filled with zeroes.

The possible values of each entry are:

• 0xFFFF : If the sector is before the data area (sectors 0-7).
• 0x0008 - 0x04CF : If this sector is part of a file but not the last sector.
  • This whole sector is part of the file.
  • The value is the number of the next sector of the file.
• 0xFC00 - 0xFFFF : If this is the last sector of a file.
  • Subtract 0xFC00 from the value to get a size. The first size bytes of this sector are part of the file.
  • If you get 0 from the subtraction, then the whole sector is part of the file. (This does not occur in the original PoP disk image, though.)
  • The unused area of last sectors is filled with 0x00. (makeimg.exe fills it with 0xE5.)
• 0x0000 : If the sector is not used or does not exist (unused entries).
  • Unused sectors are filled with 0xE5.

How to read a file

• Find the file in the #Directory.
• Read the number of the first sector into current_sector.
• Repeat until exit:
  • current_sector should be a valid sector number pointing into the data area (between 0x0008 and 0x04CF). If it's not then it's an error.
  • Read the #File allocation table entry corresponding to current_sector into next_sector. (offset = 0x400 + current_sector * 2, length = 2)
  • Read the sector numbered current_sector into sector_data. (offset = current_sector * 0x400, length = 0x400)
  • If next_sector < 0xFC00:
    • Append sector_data to the output.
    • Set current_sector to next_sector.
    • Continue the loop.
  • else:
    • Set size to next_sector - 0xFC00.
    • If size = 0 then set size to 0x400.
    • Append the first size bytes of sector_data to the output.
    • Exit the loop.
• Done.

TODO: How to make an empty disk. How to add a file.

List of files

In the order they appear in the #Directory:

file	format	contents
MUSIC.SYS	program	music player
MAIN.PRG	program	gameplay, cutscenes
SUBPROG.PRG	program	menus, intro, ending
BJLOGO.PRG	program	Broderbund logo animation
PALET.DAT	palette	the palette used by the game
FONT.DAT	font	font used in the menu, and for messages like the level number
FIRE.DAT	sprites	torch flame used on the levels
MUSIC1.MUS	music
MUSIC2.MUS	music
MUSIC3.MUS	music
MUSIC4.MUS	music
FIGHT.MUS	music
FIGHTF.MUS	music
FIGHTS.MUS	music
FIGHTK.MUS	music
VICT1.MUS	music
APPEAR.MUS	music
APPEAR2.MUS	music
PICKUP.MUS	music
POWUP.MUS	music
KUSURI.MUS	music
CLEAR.MUS	music
EXIT.MUS	music
DEAD.MUS	music
DEAD2.MUS	music
OPEN.MUS	music
ROOM1.MUS	music
ROOM2.MUS	music
END1.MUS	music
END2.MUS	music
END3.MUS	music
TIMEOUT.MUS	music
MENU.MUS	music
SOUND.EFC	sound effects	sound effects used when synthesizer hardware is available (in Neko Project 2: Device → Sounds → PC-9801-86)
BEEP.EFC	sound effects	sound effects used when only a beeper is available (in Neko Project 2: Device → Sounds → Disable boards)
JAFFER1.DAT	background	Intro: Jaffar's face
JAFFER2.DAT	background	Intro: Jaffar's hands and top half of crystal ball
JAFFER3.DAT	background	Intro: bottom half of crystal ball
OPEN1.DAT	background	Intro: In the crystal ball: the prince and the princess
OPEN2.DAT	background	Intro: In the crystal ball: the prince and the princess caught
OPEN3.DAT	background	Intro: In the crystal ball: the prince in dungeon
OPEN11.DAT	background	Intro: Waving water for OPEN1.DAT
OPEN12.DAT	background	Intro: Waving water for OPEN1.DAT
OPEN32.DAT	background	Intro: Torch flame for OPEN3.DAT
OPEN33.DAT	background	Intro: Torch flame for OPEN3.DAT
JAF_S1.DAT	background	Intro: Jaffar grinning
JAF_S2.DAT	background	Intro: Jaffar grinning
JAF_E1.DAT	background	Intro: Jaffar's eyes glowing
JAF_E2.DAT	background	Intro: Jaffar's eyes glowing
JAF_E3.DAT	background	Intro: Jaffar's eyes glowing
JAF_E4.DAT	background	Intro: Jaffar's eyes glowing
TITLE.DAT	background	Title screen: Persia at night
TITLE2.DAT	background	Title screen: game title
TITLE3.DAT	background	Title screen: copyrights
TITLE4.DAT	background	Title screen: a game by Jordan Mechner
PROOM.DAT	background	Princess's room
VCLIP.DAT	raw 1bpp image	clipping masks?
MOYOU.DAT	background	background of the main menu
TRAP.DAT	(compressed) sprites	traps, potions, doors, everything not part of the background (level objects except buttons and loose floors)
PLATE1.DAT	(compressed) sprites	buttons, loose floors for LEV01.CHR
PLATE4.DAT	(compressed) sprites	buttons, loose floors for LEV04.CHR
PLATE7.DAT	(compressed) sprites	buttons, loose floors for LEV07.CHR
PLATEA.DAT	(compressed) sprites	buttons, loose floors for LEV10.CHR
PLATEC.DAT	(compressed) sprites	buttons, loose floors for LEV12.CHR
PLATEE.DAT	(compressed) sprites	button for LEV14.CHR
CHTAB1.DAT	(compressed) sprites	prince
CHTAB2.DAT	(compressed) sprites	prince and mouse
CHTAB3.DAT	(compressed) sprites	prince and sword
CHTAB4F.DAT	(compressed) sprites	fat guard on level 6
CHTAB4G.DAT	(compressed) sprites	regular guard
CHTAB4K.DAT	(compressed) sprites	shadow on level 12
CHTAB4S.DAT	(compressed) sprites	skeleton on level 3
CHTAB4V.DAT	(compressed) sprites	the boss on level 13
CHTAB4X.DAT	(compressed) sprites	Jaffar on level 14, 15
CHTAB5.DAT	(compressed) sprites	prince
CHTAB6.DAT	(compressed) sprites	princess, Jaffar in the intro, hourglass, torch flame used in the princess's room
CHTAB7.DAT	(compressed) sprites	Jaffar in the intro
LEV01.CHR	(compressed) tiles	graphics for levels 0, 1, 2, 3 (dungeon)
LEV04.CHR	(compressed) tiles	graphics for levels 4, 5, 6 (palace)
LEV07.CHR	(compressed) tiles	graphics for levels 7, 8, 9 (dungeon)
LEV10.CHR	(compressed) tiles	graphics for levels 10, 11 (palace)
LEV12.CHR	(compressed) tiles	graphics for levels 12, 13 (dungeon)
LEV14.CHR	(compressed) tiles	graphics for level 14 (halls)
LEV15.CHR	(compressed) tiles	graphics for level 15
LEV00.MAP	(compressed) level	level 0 (demo)
LEV01.MAP	(compressed) level	level 1
LEV02.MAP	(compressed) level	level 2
LEV03.MAP	(compressed) level	level 3
LEV04.MAP	(compressed) level	level 4
LEV05.MAP	(compressed) level	level 5
LEV06.MAP	(compressed) level	level 6
LEV07.MAP	(compressed) level	level 7
LEV08.MAP	(compressed) level	level 8
LEV09.MAP	(compressed) level	level 9
LEV10.MAP	(compressed) level	level 10
LEV11.MAP	(compressed) level	level 11
LEV12.MAP	(compressed) level	level 12 (12a) (up to the Shadow fight)
LEV13.MAP	(compressed) level	level 13 (12b) (a boss, but not Jaffar yet)
LEV14.MAP	(compressed) level	level 14 (12c) (the halls leading to the princess)
LEV15.MAP	(compressed) level	level 15 (12d) (the fight with Jaffar)
DEMOPLAY.KEY	automatic moves	Automatic moves of the prince for the demo level.
EFONT.DAT	font	ending credits font
ENDING1.DAT	background	Ending: the prince bows before the sultan
ENDING2.DAT	background	Ending: the prince and the princess wave to the people
ENDING3.DAT	background	Ending: the prince and the princess together in the sunset
ENDING4.DAT	background	Ending: palace garden
ENDING5.DAT	background	Ending: "The End" text
ENDING6.DAT	background (multiple images)	Ending: waving flags

Compression

• Tools: compress.exe

The following files are compressed: TRAP.DAT, PLATE*.DAT, CHTAB*.DAT, LEV*.CHR, LEV*.MAP

Compressed data is stored as a series of blocks. Each block starts with a head byte specifying what to do, followed by 0 to 4 argument bytes.

Each block adds 4 bytes to the output, except those with head bytes 0x11, 0x21, and 0x91. Those add multiples of 4 bytes.

There is no end marker, the decompression ends when the compressed file ends.

In the arguments and the output column, each group of two letters represents a byte.

In the following table, the head bytes are ordered first by their second half, then by their first half. The system in the codes is more visible this way.

head byte	arguments	output
0x00	xx yy zz ww	xx yy zz ww (i.e. copy the next 4 bytes to the output)
0x01	-	Repeat the last 4 bytes of the output.
0x11	nn	Repeat the last 4 bytes of the output, 0xnn + 1 times.
0x21	nn mm	Repeat the last 4 bytes of the output, 0xmmnn + 1 times.
0x81	-	Repeat the penultimate 4 bytes of the output.
0x91	nn	Repeat the penultimate 4 bytes of the output, 0xnn + 1 times. Phrased differently, start from the 8th last byte of the output, and copy (0xnn + 1) * 4 bytes. If nn > 1 then the source overlaps the destination, and the bytes written will later become bytes read. This is intentional.
0x02	xx	xx xx xx xx (i.e. write the next byte 4 times to the output)
0x03	xx yy	xx yy yy yy
0x13	xx yy	xx yy xx xx
0x23	xx yy	xx xx yy xx
0x33	xx yy	xx xx xx yy
0x04	xx yy	xx xx yy yy
0x14	xx yy	xx yy xx yy
0x24	xx yy	xx yy yy xx
0x44	xx yy zz	xx xx yy zz
0x54	xx yy zz	xx yy xx zz
0x64	xx yy zz	xx yy zz xx
0x74	xx yy zz	xx yy yy zz
0x84	xx yy zz	xx yy zz yy
0x94	xx yy zz	xx yy zz zz
0xN5 (N=0..F)	ba dc	Na Nb Nc Nd (i.e. write bytes whose upper half comes from the head and their lower half comes from the arguments)
0xN6 (N=0..F)	ba dc	aN bN cN dN (i.e. write bytes whose lower half comes from the head and their upper half comes from the arguments)
0x07	xx	00 00 00 xx
0x17	xx	00 00 xx 00
0x27	xx	00 xx 00 00
0x37	xx	xx 00 00 00
0x47	xx yy	00 00 xx yy
0x57	xx yy	00 xx 00 yy
0x67	xx yy	00 xx yy 00
0x77	xx yy	xx 00 00 yy
0x87	xx yy	xx 00 yy 00
0x97	xx yy	xx yy 00 00
0xA7	xx yy zz	00 xx yy zz
0xB7	xx yy zz	xx 00 yy zz
0xC7	xx yy zz	xx yy 00 zz
0xD7	xx yy zz	xx yy zz 00
0xF7	-	00 00 00 00
0xN8 (N=0..D or F)	see above	Like 0xN7, but instead of 00, use FF.
0xN9 (N=0..D)	see above	Like 0xN7, but instead of 00, use the corresponding byte from the last 4 bytes of the output (the value from 4 bytes before).
0xNA (N=0..D)	see above	Like 0xN7, but instead of 00, use the corresponding byte from the penultimate 4 bytes of the output (the value from 8 bytes before).

Levels

• Tools: mapedit.exe

The levels are stored in the (compressed) LEV*.MAP files.

After decompression, levels contain the following data:

Offset	Size	Contents
0x0000..0x07FF	2048 (128 halfblocks * 4*4 CHR tiles)	CHR tiles of each halfblock
0x0800..0x08FF	256 (128 blocks * 2 halfblocks)	back layer halfblocks of each block
0x0900..0x09FF	256 (128 blocks * 2 halfblocks)	front layer halfblocks of each block (The most significant bit is sometimes set, what does it mean?)
0x0A00..0x0AFF	256 (128 blocks * 2 bytes)	#Block flags and objects
0x0B00..0x0DCF	720 (24 rooms * 30 tiles)	blocks (The most significant bit is sometimes set, what does it mean?)
The remaining parts correspond to the DOS / Apple II level format from offset 0x2D0.
0x0DD0..0x109F	720 (24 rooms * 30 tiles)	modifiers
0x10A0..0x119F	256	#Door events 1
0x11A0..0x129F	256	#Door events 2
0x12A0..0x12FF	96 (24 rooms * 4 directions)	room links (left,right,up,down) (1 to 24, or 0 if there is no adjacent room)
0x1300	1	number of used rooms
0x1301..0x1318	24	room row within level map (unused)
0x1319..0x1330	24	room column within level map (unused)
0x1331..0x133F	15	unused
0x1340	1	starting room (1 to 24)
0x1341	1	starting tile position (0 to 29)
0x1342	1	starting direction (0x00=right, 0xFF=left)
0x1343..0x1346	4	unused
0x1347..0x135E	24	guard tile position for each room (0 to 29=0x1D, or 30=0x1E if no guard)
0x135F..0x1376	24	guard direction for each room (0x00=right, 0xFF=left)
0x1377..0x138E	24	unused?
0x138F..0x13A6	24	unused?
0x13A7..0x13BE	24	guard skill for each room
0x13BF..0x13D6	24	unused?
0x13D7..0x13EE	24	unused? (DOS PoP stores the guard color here)
0x13EF..0x13FF	17	unused

Tiles and blocks

Tiles from LEV*.CHR files are 16×16 pixels. 4×4 tiles are combined into a halfblock (64×64 pixels). Then two halfblocks (top and bottom halves) are combined in each layer (back, front) of each block (64×128 pixels).

Blocks changed by the game

(Based on the documentation by Zarazala)

When you pick up an item or a loose floor starts falling, the block number of that tile is incremented by 1. Therefore, for each block with a potion, a sword, or a loose floor, the next block must have the same graphics and flags but no object.

TODO: What happens when a loose floor lands? There is no broken floor object. To add a broken floor, the block number has to be changed, but by what logic?

Special events which change tiles similarly increase the block number by 1. The exception is the appearing of the mirror, which decreases the block number by 1.

Block flags and objects

Only the first byte of each item is used, the second bytes are zero.

byte	meaning	notes
flags -- these can be combined with objects
0x01	floor
0x02	wall
0x04	torch	Unlike in DOS PoP, torches appear in the tile where they are placed, not one tile to the right.
objects
0x00	none
0x08	loose floor
0x10	open button	The modifier selects the door event to be triggered.
0x18	close button	The modifier selects the door event to be triggered.
0x20	door	If the modifier is 1 then the door is open, else it is closed.
0x28	spike
0x30	heal potion
0x38	hurt potion
0x40	life potion
0x48	upside down potion
0x50	slow fall potion
0x58	chomper
0x60	sword
0x68	mirror	Not used in level data: Placed on level 4 when the exit door opens.
0x70	level door
0x78	skeleton
0x80	door top
0x88	balcony stars	Used in the top left corner of balconies.

Door events

(same format as in the DOS / Apple II version)
-------------------------  7  6  5  4  3  2  1  0 <-bits
byte from door events 1 | NX R1 R0 L4 L3 L2 L1 L0
byte from door events 2 | R4 R3 R2  0  0  0  0  0

R4 R3 R2 R1 R0: The number of the room. (1..24)

L4 L3 L2 L1 L0: The location in the room. (0..29)

NX: If zero then trigger next door event, if one then don't.

Palette

The palette is stored in PALET.DAT.

It is used for the whole game, except the following:

• It does not affect the Broderbund logo animation.
• Nor does it affect the flashes of the screen when someone is hurt, etc. (those colors are in MAIN.PRG)

It contains 7 RGB color values, for palette slots 1-7. Slot 0 is not in the file, it is always black.

Each color is encoded in two bytes, with the bits arranged as: rrrrbbbb 0000gggg

That is, in the first byte, bits 0-3 store the blue intensity, bits 4-7 store the red intensity. In the second byte, bits 0-3 store the green intensity, and bits 4-7 are unused.

The default colors are:

index	bytes	HTML	color
0	-	#000		black
1	09 00	#009		blue
2	A0 00	#A00		red
3	BB 00	#B0B		magenta
4	00 08	#080		green
5	0D 0B	#0BD		cyan
6	D0 0D	#DD0		yellow
7	EE 0E	#EEE		white

Tiles

• Tools: chrconv.exe

Tiles are stored in the (compressed) LEV*.CHR files.

After decompression, they contain data for 256 tiles, each is 0x80 bytes long. The data of each tile is further split into four sections (bitplanes) of 0x20 bytes each.

To decode the image of a tile, arrange the bits of each plane in a 16×16 array. The bits should be read from bit 0 to bit 7, and the array should be filled left to right, top to bottom.

The first three planes contain bits 0, 1, and 2 of the color indices for each pixel. These are then combined into a three bits-per-pixel image.

With the default palette, these bitplanes roughly correspond to blue, red, and green components, respectively. I say "roughly" because the intensity of the enabled components is different for different colors.

The fourth plane contains transparency masks, but they are used only for tiles in the foreground layer? Each bit of the transparency mask is 0 for transparent parts and for some backgrounds, 1 otherwise.

chrconv.exe treats the transparency mask as bit 3 of the color index.

The 256 tiles should be displayed in a 16×16 arrangement, this keeps related tiles together.

Backgrounds

• Tools: picconv.exe

Backgrounds are images without transparent parts. They don't necessarily fill the screen.

Backgrounds have this header:

• 2 bytes: Width in bytes. Multiply by 8 to get the width in pixels.
• 2 bytes: Height in pixels.

After the header comes the image data. The image data is compressed, but with a different method than described in #Compression.

The basic idea is the same, though: Compressed data is stored as a series of blocks. Each block starts with a head byte specifying what to do, followed by 0 to 3 argument bytes.

Backgrounds decode into three bitplanes, similarly to #Tiles, except the bytes of the planes are interleaved.

Each block adds 3 bytes to the output, or rather, one byte to each of the 3 bitplanes. The exceptions are the blocks which repeat bytes. These add multiples of 3 bytes, or, the same number of bytes to each bitplane.

There is no end marker, the decompression ends when the compressed file ends (or when the output has enough bytes?).

In the arguments and the output column, each group of two letters represents a byte.

In the following table, the head bytes are ordered first by their second half, then by their first half. The system in the codes is more visible this way.

head byte	arguments	output
0x00	nn	Repeat the next 3×1 bytes of the output 0xnn times.
0xN0 (N=1..F)	-	Repeat the next 3×1 bytes of the output N times.
Note: The above two codes are a bit tricky. When you see a head byte ending in 0, don't write anything into the output yet. Just set a flag which reminds you that you need to repeat, and also store the value of nn or N as repeat_count. Every time after you processed a block which is not a "repeat next" block, check if the repeat flag is set. If it is, then repeat the last 3×1 bytes repeat_count times.
0x01	xx	xx xx xx (i.e. write the next byte 3 times to the output)
0x02	xx yy	xx xx yy
0x12	xx yy	xx yy xx
0x22	xx yy	xx yy yy
0x03	xx yy zz	xx yy zz (i.e. copy the next 3 bytes to the output)
0x04	xx	00 00 xx
0x14	xx	00 xx 00
0x24	xx	xx 00 00
0x34	xx yy	00 xx yy
0x44	xx yy	xx 00 yy
0x54	xx yy	xx yy 00
0x05	xx	FF FF xx
0x15	xx	FF xx FF
0x25	xx	xx FF FF
0x35	xx yy	FF xx yy
0x45	xx yy	xx FF yy
0x55	xx yy	xx yy FF
Note: 0xN5 head bytes are like 0xN4 head bytes, except they use 0xFF instead of 0x00.
0x06	-	00 00 00
0x16	-	FF 00 00
0x26	-	00 FF 00
0x36	-	FF FF 00
0x46	-	00 00 FF
0x56	-	FF 00 FF
0x66	-	00 FF FF
0x76	-	FF FF FF
Note: A 0xN6 head byte basically appends 8 pixels with color N. The appended bytes are filled with bits 4, 5, and 6 of the head byte, respectively.
0xR7	nn	Go up R+1 scanlines from where you are (i.e. go back (R + 1) × width in bytes × 3 bytes), read 0xnn × 3 bytes from there, and append them to the output.

ENDING6.DAT

ENDING6.DAT has a slightly different format, because it contains multiple images.

The file begins with 12 offsets, 2 bytes each. These offsets tell where each image starts in the file.

The images themselves are in the same format as the other #Backgrounds.

Sprites

• Tools: patview.exe

Sprites are in the files FIRE.DAT, CHTAB*.DAT, PLATE*.DAT, TRAP.DAT. They are compressed, except for FIRE.DAT.

The files begin with the following header:

• 2 bytes: The number of images.
• For each image:
  • 2 bytes: The offset part of the address. (Always in 0x0..0xF?)
  • 2 bytes: The segment part of the address.
  • To get the actual start address of the image, calculate segment * 16 + offset.
  • This strange form of addressing comes from the x86-compatible CPU in the PC-98.

The images are in the following format:

• 1 byte: Width in bytes. Multiply by 8 to get the width in pixels.
• 1 byte: Height in pixels.
• Data.

The data of the sprite images can decompressed in the following way:

• Repeat until you have width in bytes × height × 4 bytes in the output:
  • Read a head byte.
  • If head byte >= 0x80:
    • Append (head byte - 0x80 + 1) × 4 zero bytes to the output.
  • else:
    • Copy the next (head byte + 1) × 4 bytes from the input to the output.

The resulting output consists of four interleaved bitplanes.

• To decode, go through the output four bytes at a time.
  • Within each group, the first byte belongs to the first bitplane, the second byte to the second bitplane, and so on.
• The first three planes contain bits of the color indices, while the fourth contains a transparency mask.
  • Each bit of the transparency mask is 0 for transparent pixels, 1 otherwise.
  • patview.exe treats the transparency mask as bit 3 of the color index.
• The bits in the bitplanes are arranged in the same way as in tiles and backgrounds: the bits from bit 0 to bit 7 go into 8 pixels from left to right.
• But the order of bytes is different: Each byte corresponds to a block of 8 pixels, below the previous block.
  • This will first fill a vertical strip of 8 pixels on the left side of the image.
  • When you reach the bottom of the image, continue at the next vertical strip of 8 pixels.

Fonts

Fonts are stored as a sequence of 1-bits-per-pixel images. The bits within a byte correspond to pixels in the same way as for other images, but now there is only one bitplane.

The size of the images and the included characters depend on the font.

File	number and size of glyphs	contained characters	notes
FONT.DAT	48 glyphs of 16×16 pixels (32 bytes) each	0-9 A-Z . , / # (followed by 8 empty images)	"#" appears as the symbol of the Enter key: ↵⃣
EFONT.DAT	45 glyphs of 24×24 pixels (72 bytes) each	A-M O P S T Y a-i k-p r-w y z ( ) - .	missing letters: N Q R U-X Z j q x

For FONT.DAT, the advance width of all glyphs is 16 pixels.

SUBPROG.PRG contains the following information about EFONT.DAT:

• Offsets 0x556E..0x55CD contain a mapping table from the ASCII codes 0x20..0x7F to the (1-based) glyph indices in the font.
  • Zero means the font has no glyph for the character.
• Offsets 0x55CE..0x55FB contain the advance width for each glyph, in pixels.
  • The table has 46 bytes, one more than glyphs in the font. Perhaps the last item is for the space?

The font used on the images in TITLE2.DAT and TITLE3.DAT is similar to the font in EFONT.DAT, but it has slightly shorter capital letters.

Japanese font

The game does not contain font for Japanese text. Instead, it uses the 16×16 font contained in the ROM of PC-98. (FONT.ROM in Neko Project 2.)

The game transforms that font slightly:

• In the menu, the font is made thicker.
  • This is done by drawing each glyph twice, the second time offset by one pixel to the side.
• In the intro, the font is made thicker as above.
  • Additionally, a black outline is added to the glyphs, and they are filled with a gradient which goes from yellow at the top to white at the bottom.

TODO

• Music and sounds
• Texts?
• User disk
• Automatic moves (DEMOPLAY.KEY)
• FM Towns version (PRI1.DAT)
• Hacks for easier playtesting: skipping the Broderbund logo, starting any level.
• VCLIP.DAT
• the hit point images in MAIN.PRG
• the Broderbund logo in BJLOGO.PRG (BJ = Broderbund Japan?)

External links

• Documentation and tools by Zarazala, and the game itself.