FX Graphics
Piken (FDwR_at_hotmail)
2003-04-04 / 1999-02-24
http://members.tripod.com/FDwR/snes.html


This is simply a little I've found out on my own while browsing through the data.
Unlike the graphics formats used by the SNES, the ones used by the Fx chip are
completely linear; there are no tiles or bitplanes to mess with. Everything is
stored in a large 256 bytes wide bitmap. Each adjacent pixel column of the same 
graphic image is a byte apart, but there are actually two pixels per byte. This 
is because there are two separate images interleaved in the same space, one 
using the lower four bits and the other using the upper four bits. So even 
though each of the two image planes is 256 pixels wide, there are actually 512 
pixels per row. It can look confusing with the two images overlayed together, so 
one or the other simply needs to be ANDed off. For speed's sake though, the 
graphics are all left uncompressed and can be directly accessed from ROM.

A few locations to look for familiar fx images:

<Mario 2>
  1114112          Character graphics
  1835008          All the level icons

<StarFox>
  590336           Planets, starfields, lasershots...