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I would have bet there is need of a shift in 8bpp palette, but since this fixes more than the opposite I had probably made something wrong...

I wouldn't think so. palette RAM is 512 bytes, at 15 bits per entry.

As far as stuff broken on 8bpp, though, the palette bits in the tilemap do have a use. you can turn the palette selection and palette-ized color into a direct color mode. If I knew what was broken, I could cross-reference with some of my "known places that use this feature" lists and see. (Actraiser II for Direct Color)

512/2=256...8 bpp = 256 colors per entry

I need something that uses direct color without mode 7 anyway...

According to Overload (author of Super Sleuth):


I know Secret of Mana is a world map (and you'll spend longer getting to that point than you will on the bug itself!)


According to my notes (which may not reflect newer findings):
the palette entry itself (0-255) takes the form bbgggrrr and the tilemap palette selection becomes bgr. The palette index supplies the top bits, palette select the next bit, and the rest are 0. (That is, blue = iit00, green/red are iiit0, where t is the palette selection in the tilemap, and the other is the palette index taken from the tile)

Does that match your documents?

Yes, matches, also there's a bug on color calcs even in mode 7 that I need to fix.

EDIT: calcs were right but applied on the wrong layer. And I've lost hopes to find something that uses mode 3/4 + direct colors --"

Supposedly, Secret of Mana uses direct color + mode 3 for one of the world maps. that's a good 20+ hours of gameplay to reach, though.

It should work the same as mode 7, except that mode 7 doesn't have 3 palette bits in the tilemap.

What modes are those last two shots actually in? The first one is obviously Mode 7. The second very well could be (possible logo tricks like Actraiser pulls). The third would be... strange. That looks like a classic place to use Mode 3.

It's mode 7 for all of three snaps, first two are Aerobiz, the third is Romance of the Three Kingdoms 2 (it uses zooming effects etc.). And, guess that I need to play Secret of Mana and at least I have an original SNES USA cart, I just need to check if I still have a valid save...

r5426 /src/mame/video/snes.c: [SNES]: Fixed direct color gfxs in mode 3/4, also fixed color data shifting in both modes.


Many thanks to Lord Nightmare for the save file.



Color shifting is the first thing that MESS does what other snes emus don't afaik. Ideally if you should do a color conversion to a framebuffer and you can't completely fill that framebuffer, you should fill the remaining data with the most significant bytes of the color offsets.
Comparison:

before:


after:

Is this "color shifting" the same as RGB channel depth promotion doing texture lookups?
Example: if the render target is 888 and the texture is 565 RGB format then the hardware will promote the bits like this:

destination R [7:0] <- source (R4, R3, R2, R1, R0, R4, R3, R2)

Yes, exactly like that