B_IINC and Jaguar Doom

[Csonicgo]

I have a friend who is making a "PC" port of Jaguar Doom , and he ran into some colour issues as it pertains to the B_IINC:

 

Ok but in the original jag code, is each pixel being drawn as a CRY16 value with the Y component further being being decremented as necessary, or what? Like take a dark red in Doom which I assume is internally represented with a saturated-red chroma and a luminance of 33/256 or whatever. Does the darkening effect result in the red being initially multiplied by 33/256(to get to the normal dark red color) and then further darkened by some sort of second operation?

 

Since the gouraud registers say they only work in CRY color mode, I have to assume the luminance adjustment requires the pre-separated luminance and color components that this color space offers - because the Jaguar can do RGB color as well, just outputting it straight into the video signal encoder - but not with all of the features of the hardware. Right now I'm literally adding B_IINC directly to the scaled up Y component, because this is the best idea I can come up with to make it work. Nobody has actually documented exactly what the hardware does with B_IINC, not even the Jaguar tech documents bother to explain it, and none of the half-finished Jaguar emulators that exist implement it either.

 

Anyone out there deciphered B_IINC's actual behaviour yet? This documentation (and this) isn't cutting the mustard.