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correct bg collision doc

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Michael Miceli 2024-06-22 16:40:59 -04:00
parent 961aa789c2
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docs/Graphics Documentation.md
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@ -185,25 +185,14 @@ is 4 columns wide and 4 columns tall, a single super-tile has 4 collision code
points: top left, middle left, middle top, and middle middle.
Each byte in `BG_COLLISION_DATA` can be broken down into 4 collision codes.
Every 2 bits represents the collision code (0, 1, 2, or 3) for one of the 4
points in the super-tile. The first 8 bytes are for the top rows of collision
points for a single nametable row. The next 8 bytes are the middle collision
points. This pattern repeats until all of the first nametable data is specified
and then is repeated for the 2nd nametable. For a given background collision
entry, add #$04 to determine the next row down. The following is an example of
the byte offsets from `BG_COLLISION_DATA` for the top left nametable. Note that
next nametable starts at offset #$40 and not #$38.
Note that this is similar in structure to the attribute table.
* Each byte contains data for a #$0f (16) nametable tiles
* Each 2 bits within the byte specifies data for 4 nametable table tiles (2x2
area).
However, the offsets within the structure refer to different areas of the
nametable. Unlike the attribute table, where each byte specifies a 4x4 area of
pattern table tiles, the background collision data byte specifies data for a 2x8
area of pattern table tiles. The table below shows how the background collision
data is arranged on the nametable.
Every 2 bits represents the collision code (0, 1, 2, or 3) for every other
pattern table tile. The first 4 bytes are for the top row of collision points
for a single nametable row. The next 4 bytes are the next nametable row of
pattern table tiles. This pattern repeats until all of the first nametable data
is specified and then is repeated for the 2nd nametable. For a given background
collision index, add #$04 to determine the next row down. The following is an
example of the byte offsets from `BG_COLLISION_DATA` for the top left nametable.
Note that next nametable starts at offset #$40 and not #$38.
```
00 00 00 00 01 01 01 01 02 02 02 02 03 03 03 03