I've started work on implementing the auto-steel. This will be the last thing added before V1.03n is released, and once this is done, I should be able to pump out NeoLemmix-adapted versions of all players *very* quickly, since all I'll have to do is adjust objects and test for solvability of levels under the new conditions. (I probably won't do any upfront testing on the official games' levels, but I will test LPII and LPII Bonus.)
So far, I've successfully gotten the game to draw *only* the steel pieces. Still need to take into account other pieces overwriting/erasing it though. (This could in a roundabout way solve the issue of whether something drawn over steel cancels the area or not - if you want it to cancel it, place the steel block first then place the other piece over it; if you don't, place the other piece first then place the steel block with No Overwrite. Making it pay attention to the steel's own No Overwrite, it appears, would require some VERY heavy modifications, and I think in this case, due to both being far simpler and allowing more choice, it's easier to leave the burden on the level design.)
EDIT: Got it all working, pretty much exactly via the methods I described. There are three new level options. All of them are set in the high byte of the extended graphic set number; I chose to use this one as it's probably the least frequently used, I doubt many people will be too bothered by only being able to have 254 VGASPECs instead of 65534 of them (especially between DOS only having supported up to 10 of them and custom standard graphic sets being possible nowdays - as well as that NeoLemmix supports 24 custom colors plus the 8 fixed ones in custom graphic sets, while VGASPECs are still limited to 8 colors and I don't really plan on trying to extend this), and the DOS versions in fact ignore this byte altogether rather than treating the two bytes as a 16-bit number.
The settings are:
1 - Enable steel erasing. When this is set, the first 16 steel areas function as normal, while the last 16 negate steel instead of adding it. (They do not negate ANYTHING else, only steel; but they can negate the automatic steel as well as manually-placed steel.)
2 - Enable autosteel. Requires support in the graphic set. (It's a very simple change to add this to a graphic set.)
4 - Ignore steel data in level. Use this if you don't want the level's steel data to be read (because, perhaps, you're testing the level with autosteel), but still want to keep the data in the level file.
EDIT: 8 - When applying autosteel, ignore overlapping terrain, just make all solid parts of the steel block into steel areas. (Currently it ignores erasers too, I plam to change this.)
I just want to test this a bit further (EDIT: and make the 4th bit *not* cause ignoring erasers), and then I'll upload V1.03n CustLemmix; with V1.03n LPDOS probably not far behind. This will GREATLY simplify porting existing packs (and designing new ones); since now I only have to adjust objects.
I've found that both the "overwriting terrain cancels steel" and "overwriting terrain doesn't cancel steel" options to be useful. Just have a look at which one works better for Taxing 2, then which one works better for Mayhem 1, and you'll soon see my logic in deciding to go with giving the option after all (even if it potentially sacrifices consistency). I would also say though, while the pay-attention-to-other-terrain seems more logical; given how steel areas are laid out by default, I would say it goes against the intentions of the designers, so the paying attention to overlapping (non-erasing) terrain would probably be an option left more for custom levels than conversions of the official packs.
I've also added an option so that a player can be compiled with any of those options globally activated (except bit 1; I see no need to add that functionality for that). This'll speed up the official pack conversions even more.
For anyone making custom styles; this does indeed mean you're no longer restricted to rectangular terrain; you can make it any shape you want and the auto-steel will use the exact shape of it.
I'm mostly just happy that this means I don't have to align the steel areas manually for the official and LPII levels (except "The COVOX Level", since it uses a VGASPEC).