Sonic the Hedgehog CD (PC)

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This is the Sonic Community Hacking Guide for the DirectX PC Version of Sonic CD.
Note: All data is little endian.
Any reference to a file name with ??? should be replaced by the Round, Zone and Time Period. Thus, DLL???.dll for Palmtree Panic Zone 1 Present is DLL11A.dll.

Level editing

Note that the current version of SonED2 modifies some level data during the extraction process. This page documents the original formats, which SonLVL can open.

Object placement

This data is located in the DLL???.dll file in each level's folder. See below for locations.
Each time period of each Zone shares an object list, so that the game can remember that you destroyed an enemy in the past, and not show it in the present.

There are eight bytes in one object definition. The first two bytes are the X position of the object. The next two bytes, broken down in bits, have the format AB00 YYYY YYYY YYYY, where A is the vertical flip flag, B is the horizontal flip flag and YYYY YYYY YYYY is the Y position of the object. The 5th byte is the reference number on the object pointer list, with the most significant bit if set indicating that the object should be assigned an entry on the object respawn table, and the 6th byte is an optional declaration to use for defining that object's behavior and/or animation. This will depend on the object. The last two bytes, broken down in bits, are ABC0 0000 0000 0000, where A indicates the object should appear in the past time period, B indicates the object should appear in the present time period, and C indicates the object should appear in the future time period.

Level layout

This data is located in the DLL???.dll file in each level's folder. See below for locations.
Level layouts are pretty simple. They are 64x8 chunks, there is one byte per 256x256 chunk to place on the map. The blocks are put together from left to right, top to bottom.

8x8 tiles

This data is located in the TCMP???.cm_ file in each level's folder, and is a SCRL file. The tiles will always have a width and height of 8x8.

16x16 block mappings

This data is located in the T???.map file in each level's folder.
16x16 block mappings consist of four 8x8 tiles, arranged in the shape:

0	1
2	3

Each 8x8 tile is represented by one word, which like all SEGA Mega Drive VDP pattern indices, is a bitmask of the form PCCY XAAA AAAA AAAA. P is the priority flag, CC is the palette line to use, X and Y indicate that the sprite should be flipped horizontally and vertically respectively, and AAA AAAA AAAA is the actual tile index, i.e. the VRAM offset of the pattern divided by $20.

256x256 Chunk mappings

This data is located in the Map???.bin file in each level's folder.
256x256 chunk mappings consist of 256 16x16 tiles, arranged in the shape:

0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47
48	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63
64	65	66	67	68	69	70	71	72	73	74	75	76	77	78	79
80	81	82	83	84	85	86	87	88	89	90	91	92	93	94	95
96	97	98	99	100	101	102	103	104	105	106	107	108	109	110	111
112	113	114	115	116	117	118	119	120	121	122	123	124	125	126	127
128	129	130	131	132	133	134	135	136	137	138	139	140	141	142	143
144	145	146	147	148	149	150	151	152	153	154	155	156	157	158	159
160	161	162	163	164	165	166	167	168	169	170	171	172	173	174	175
176	177	178	179	180	181	182	183	184	185	186	187	188	189	190	191
192	193	194	195	196	197	198	199	200	201	202	203	204	205	206	207
208	209	210	211	212	213	214	215	216	217	218	219	220	221	222	223
224	225	226	227	228	229	230	231	232	233	234	235	236	237	238	239
240	241	242	243	244	245	246	247	248	249	250	251	252	253	254	255

Each 16x16 tile has a two-byte value with the format 0SSY X0II IIII IIII. SS is the solidity of the tile - 00 means not solid, 01 means top solid, 10 means left/right/bottom solid, and 11 means all solid. Y is the Y-flip flag, X is the X-flip flag, and II IIII IIII is the index of the 16x16 tile to use.

Palettes

This data is located in the DLL???.dll file in each level's folder. See below for locations.
Unlike all the Mega Drive games, and even Sonic & Knuckles Collection, this port does not use Mega Drive palettes. Instead, palette entries take four bytes, in the format RR GG BB 01, allowing for over 16 million shades instead of the Mega Drive' 512.

DLL Breakdown

DLL11A.DLL

Offset	Type	Length	Description
18C70	Palette	40	Palette line 1
18CB0	Palette	C0	Palette lines 2-4
19818	Object Layout	F90
1CE60	Level Layout	200	Foreground layout
1D060	Level Layout	200	Background layout

Sound Effects

Sound effects are stored in the PCM8.CMP file, in 8-bit unsigned Mono at 11kHz. The file begins with a header that begins like this:

Offset	Type	Description
0	String	"OTHE"
4	Pointer	End of File
8	4 Bytes	Number of Sound Effects
C	Pointer	Sound Effect data

After this, there is a 4 byte value for each sound effect describing its length in bytes, then the sound data as raw PCM. SCDPCsnd can edit this file by importing and exporting WAV files.

Sprites

This data is located in SCMP*.cm_ files, and is SZDD compressed. Windows comes with an expand.exe program that can decompress these, or you can use EXPAND.EXE and COMPRESS.EXE from SonED2's Sonic CD PC folder.

The file begins with a header that begins like this:

Offset	Type	Description
0	String	"SPRT"
4	Pointer	End of File
8	4 Bytes	Number of Sprites
C	Pointer	Sprites

After that, there are 0xC bytes of data for each sprite:

Offset	Type	Description
0	2 Bytes, signed	X Offset
2	2 Bytes, signed	Y Offset
4	2 Bytes	Width
6	2 Bytes	Height
8	2 Bytes	Offset in palette to start at, plus 16
A	2 Bytes	C1 2B

Following that is the sprite data, in 4bpp. Each sprite takes height * (width / 2) bytes, and the next sprite follows immediately. If a sprite's width is not divisible by eight, it is padded to be divisible by eight.

Tiles

This data is located in the TCMP*.cm_ files, and is SZDD compressed. Windows comes with an expand.exe program that can decompress these, or you can use EXPAND.EXE and COMPRESS.EXE from SonED2's Sonic CD PC folder.

The file begins with a header that begins like this:

Offset	Type	Description
0	String	"SCRL"
4	Pointer	End of File
8	4 Bytes	Number of Tiles
C	Pointer	Tiles

Following that is four sets of 2 byte values, counting the number of tiles that use each palette line. Then there are two 2 byte values for each tile indicating its width and height.

Following that is the tile data, in 4bpp. Each tile takes height * (width / 2) bytes, and the next tile follows immediately.