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register register!

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Lokathor 2018-11-21 09:36:00 -07:00
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commit 684952e752
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22
book/src/ch03/regular_backgrounds.md
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@ -237,7 +237,24 @@ separate groups of related registers.
Each of these are a read/write `u16` location. This is where we get to all of
the important details that we've been putting off.
TODO: don't put it off any longer!
* 2 bits for the priority of each background (0 being highest). If two
backgrounds are set to the same priority the the lower numbered background
layer takes prescience.
* 2 bits for "character base block", the charblock that all of the tile indexes
for this background are offset from.
* 1 bit for mosaic effect being enabled (we'll get to that below).
* 1 bit to enable 8bpp, otherwise 4bpp is used.
* 5 bits to pick the "screen base block", the screen block that serves as the
_base_ value for this background.
* 1 bit that is _not_ used in regular mode, but in affine mode it can be enabled
to cause the affine background to wrap around at the edges.
* 2 bits for the background size.
The size works a little funny. When size is 0 only the base screen block is
used. If size is 1 or 2 then the base screenblock and the following screenblock
are placed next to each other (horizontally for 1, vertically for 2). If the
size is 3 then the base screenblock and the following three screenblocks are
arranged into a 2x2 grid of screenblocks.
### Background Offset
@ -268,5 +285,4 @@ it will loop.
## Mosaic
TODO: talk about mosaic? It's just one small side step, and you can set it with
a register we just talked about, so might as well.
TODO: talk about mosaic.