From 684952e752c10c281dc963c3b543000bad4d792f Mon Sep 17 00:00:00 2001 From: Lokathor Date: Wed, 21 Nov 2018 09:36:00 -0700 Subject: [PATCH] register register! --- book/src/ch03/regular_backgrounds.md | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/book/src/ch03/regular_backgrounds.md b/book/src/ch03/regular_backgrounds.md index 8e2f154..bbcef9f 100644 --- a/book/src/ch03/regular_backgrounds.md +++ b/book/src/ch03/regular_backgrounds.md @@ -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.