Fog

[Ian]

Fogging works pretty well in most games. But I unexpectedly found this



And the real hardware ..



I thought originally there was something missing from the 2D code with regards to fog, but now I think it's something else. Must be one of the unimplemented fog parameters 'scroll fog' or something we have overlooked in the viewport code.

[Ian]

Well it turns out in the screenshot above the fog was simply missing because the value was negative >_<
The model 3 seems to ignore the sign for fog gradients.

The missing 2D fog, I'm about 90% sure is the scrollFog parameter in the viewport. I think it's a transparency value that's used to blend a colour over the bottom 2D layer.

[Jiterdomer]

From what I saw in a non-emulated video, an example of it was in this video:

https://youtu.be/wKBbwUtmmPY (Go to 5:34, the darkness of the video was actually from the user's capture card)

What Sega did to these 2D backgrounds to emulate fog effects is just cycling random colors to corresponding stages in the hardware itself rather than just making the whole background being photoshopped to white or darken the still backgrounds on the game's rom (Dural's Jeffrey stage which was showcased in that video), which Sega wanted to put Model 3 hardware to the test.