SCHG:Sonic the Hedgehog 3 & Knuckles/Level Editing
From Sonic Retro
| SCHG: Sonic the Hedgehog 3 & Knuckles |
|---|
| Main Article |
| Art Editing |
| Editing Art |
| Object Editing |
| Editing Objects |
| Level Editing |
| Editing Levels |
| Music Editing |
| Editing Music |
| RAM Editing |
| Editing RAM |
| Sonic & Knuckles Collection |
| Sonic & Knuckles Collection |
Level Layout
Level layouts are stored uncompressed in the ROM, and the format they use differs significantly from the format used in Sonic 2, allowing much larger levels.
The layout starts with an 8 byte header describing the layout. The first word of this header is the number of 128x128 tiles that make one foreground row, and the second word is the number of 128x128 tiles that make one background row. The third word is the number of foreground rows, and the fourth is the number of background rows.
Next is a list of 64 word-sized pointers in RAM. Each row of 128x128 tiles has two pointers - one for the foreground data and one for the background data. The maximum level height is thus (64 / 2 * 128) = $1000 pixels, double the maximum level height for Sonic 2.
The actual rows data (beginning at byte $88) is very simple - there is one byte per 128x128 tile, and the blocks are put together from left to right.
16x16 Block Mappings
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 Genesis 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.
128x128 Block Mappings
128x128 block mappings consist of sixty-four 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 |
Each 16x16 tile has a two-byte value with the format SSTT YXII IIII IIII. SS is the solidity of the tile in the alternate collision layer - 00 means not solid, 01 means top solid, 10 means left/right/bottom solid, and 11 means all solid. TT is the solidity of the tile in the normal collision layer - 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.