Color Math Emulation Bug

[jwdonal]

I've tried this test ROM in several other emulators (no$sns, higan, snes9x, etc) and it looks correct. However, when running in bsnes-plus the fog/clouds are displayed with a different random color on each power-on/reset/load/reload. I'm running v073+3a.

translucent.zip

[jwdonal]

Another discovery. This issue only occurs with bsnes-accuracy.exe, it does not happen with bsnes.exe.

[mrehkopf]

Seems to happen on purpose - the constant color register (writable via $2132, IIRC they call it COLDATA) is probably random on powerup on a real PPU.
Palette color 0 is the background color for the Main Screen; the "Constant Color" can be considered the background color for the Sub Screen, e.g. the background color for BG3 when used as a pure Sub Screen layer for color math.
The attached test ROM doesn't initialize the constant color via $2132 (should write $E0 - upper 3 bits to select the color channels, 5 bits for the intensity value).

[devinacker]

Yeah, as others have mentioned, this is a result of recent versions randomizing some system state by default (even more so with the accuracy core) more or less the same way higan does it.

You can disable snes.random in your config file if you want, though it's not really recommended if you're trying to match the behavior of real hardware.