Unused bit test

[Bart]

lost world

header[0] hex fc0ffcd0

The link bits are all unused -- Lost World doesn't use vertex strips?

[Ian]

Yeah that's strange.. I guess it doesn't.
Well I tried a few more games, and basically it appears all bits are set. But my feeling says that, probably some are uninitialized or simply ignored.
If only we could test out something on real hardware ..

[Bart]

Yeah that's strange.. I guess it doesn't.
Well I tried a few more games, and basically it appears all bits are set. But my feeling says that, probably some are uninitialized or simply ignored.
If only we could test out something on real hardware ..

Unfortunately my VF3 PCB is 2,700 miles away and I think I damaged the EPROM sockets. Building a custom hardware interface for uploading software, or even an EPROM emulator, would be quite a lot of work but it's something I'd like to do at some point.

Hopefully by end of week I'll at least be able to automatically generate screenshots with the various bits highlighted.

[Ian]

Probably the 'easiest' thing to do would be to modify some of the ROM models in a game and see how the h/w renders them

[Bart]

Good idea, but we would want all possibilities to be embedded simultaneously, and then they'd have to be easily verifiable. They would have to be polygon RAM models and even then, a subroutine would have to be hooked in to make the actual modifications because those models reside in mask ROM rather than on the easily-programmable EPROMs.

One solution might be to try different combinations of settings over the different characters in VF3's selection screen.

If the Scud Race debug menu uses polygon RAM, I could try to reverse engineer this menu and inject a feature that allows arbitrary bits to be flipped. Unfortunately, I think that it actually uses VROM models, which we could not reprogram (no EPROMs available to fit those sockets).

Hijacking VF3's character selection menu seems the best bet...

[Ian]

One thing I got stuck with, as the contour or alpha test. Its clearly used for all the texture types (even opaque). With proper texture filtering it will interpolate the alpha values, so you need quite a hard threshold. But in sega rally 2 the contour bit is set for the halo over the lights. But you really only want to set the alpha test value to only chuck out values that are zero. I set it to like 50%, which is half wrong for everything.

But for some reason I couldn't understand the contour bit is set for the stickers on the cars in datyona, which made me wonder if that bit was correct at all. Also the API has reference to actually being able to set the contour threshold. Wonder if thats in the header somewhere ..

[Bart]

One thing I got stuck with, as the contour or alpha test. Its clearly used for all the texture types (even opaque). With proper texture filtering it will interpolate the alpha values, so you need quite a hard threshold. But in sega rally 2 the contour bit is set for the halo over the lights. But you really only want to set the alpha test value to only chuck out values that are zero. I set it to like 50%, which is half wrong for everything.

But for some reason I couldn't understand the contour bit is set for the stickers on the cars in datyona, which made me wonder if that bit was correct at all. Also the API has reference to actually being able to set the contour threshold. Wonder if thats in the header somewhere ..

Ville believes header[5] is mostly, if not entirely, texture related. Maybe those mysterious 12 bits have something to do with it? They are set to all 1's for untextured polygons, he says. Although, 12 bits of precision are too much for a countour threshold. I would expect only 5 bits to be used, at most. Maybe that field in header[6] has something to do with it?

[Ian]

I would expect 4 bits for a contour threshold, because the model 3 textures only really support 4 bit transparency. Maybe texture interpolation gives more.
Has Ville taken an interest in development again ?

[Bart]

I would expect 4 bits for a contour threshold, because the model 3 textures only really support 4 bit transparency. Maybe texture interpolation gives more.
Has Ville taken an interest in development again ?

Yup, I think he's been looking at things for MAME.