Difference between revisions of "Block mappings"
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S=Solidity, Y=flipY, X=flipX, I=Index | S=Solidity, Y=flipY, X=flipX, I=Index | ||
Revision as of 03:24, 9 June 2008
Block mappings are used to arrange large amounts of 8x8 tiles into larger tiles (16x16, followed by 128x128 or 256x256). These larger tiles are then arranged into the level layout.
Contents
16x16 tiles
Games
Format
16x16 tiles 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 tiles
Games
Format
128x128 tiles consist of sixty-four 16x16 tiles.
SSSS YXII IIII IIII
S=Solidity, Y=flipY, X=flipX, I=Index
Each 16x16 tile has a two-byte value with the format XYYY, where YYY is the index number of the 16x16 tile to be displayed, and X is the solidity of the tile. These are possible values for X:
======================= value high low ======================= 0 not not 1 not top 2 not l/r 3 not all 4 top not 5 top top 6 top l/r 7 top all 8 l/r not 9 l/r top A l/r l/r B l/r all C all not D all top E all l/r F all all
Additionally, add the following values to YYY to change the display mode of the 16x16 tile:
400 flip x 800 flip y C00 flip x+y
256x256 tiles
Games
Format
Similar to 128x128 tiles. Values for X are:
================ value solid ================ 0 not 2 top 4 l/r 6 all 8 not A top C l/r E all
Add the following values to XYYY to change the display mode:
0800 flip x 1000 flip y 1800 flip x+y