1. This is a glitch that's slipped through the cracks. Although I believe there is feedback (although not specific to which lemming was highlit) in that it plays a sound upon highlighting. IMO it's a minor enough glitch that there's no need to release an extra update to fix it. (If you
really want to see which lemming you've highlit, eg in a crowded situation, advancing or reversing one frame will make it display, no need to fully unpause.)
2. Ceasing gameplay when the last lemming leaves is consistent with other engines -
including Lix, I believe. The difference here is that NeoLemmix doesn't have a "restart level with replay" function when level ends; however this is definitely something that can be added for V2.00n.
In regards to the IRC discussion, Akseli is completely correct about
all cases involving NeoLemmix, as well as involving a Lemmix player (including traditional CustLemmix used for playtesting traditional Lemmix levels from the NeoLemmix editor). The traditional Lemmix editor (ie: EricLang's version unmodified) does not provide a results screen full stop, but rather "freezes" once the last lemming leaves (in quotes because it's not a freeze in the sense of crashing; just as in it stops doing anything until you exit playtest mode); a replay can still be saved at this point IIRC but the Lemmix Editor has a different hotkey than the various (Neo)Lemmix players do. I can't say for sure though, as I never really used the traditional Lemmix editor (personally I preferred LemEdit back then, and used Lemmix players for playtesting).
3. This is nothing to do with EricLang's code and is a NeoLemmix feature. Since Lemmix did not support alpha blending (and the same holds true currently for NeoLemmix, although the latter does support alpha channel
data in its files; it just doesn't make use of that data currently), EricLang's code repurposed the alpha channel of the image for other uses, such as marking a pixel as solid (to differentiate between "blackground, non-solid black" and "solid black like eg. in the Crystal set", according to source code comments). Virtually all functions that need to check if there's terrain at a given pixel - including that of determining the "draw on terrain" function - check this rather than checking the color of the pixel. NeoLemmix simply takes this a bit further; with "is this pixel solid for the purpose of Draw On Terrain?" and "is this pixel solid for the purpose of lemmings interacting with it?" are two different things; although the former never happens without the latter. One-way walls (as in the trigger areas of them) are also not applied to pixels that are not "solid" for the purpose of Draw On Terrain. When desgining a level, the level designer can choose which terrain pieces do or don't set the "solid for Draw On Terrain" flag for their pixels. The end result is - one way walls do not have to have smooth edges when intersecting with other terrain (rather than with non-solid area), unlike in DOS L1 / traditional Lemmix. (On a side note, this may have to be handled differently in V2.00n, as I intend to support alpha blending properly.)
4. I will keep this in mind.