Thought it might be the division lines which is why I tried removing them, but the remaining difference is tiny and only pops up when measuring 3+ "sets" of 8 frames. I'll just have to try my best to superimpose my new arms over the old ones and see how it ends up fitting.
I've already done a camera facing sitting frame for the Veronian that's 4 pixel height difference, imagine that. If OpenXcom could include a smarter AI (At least for higher difficulties) than the original that would be pretty grand
Let's see if I can list and classify all the different arm sets in order from looking at them now (you said they should match your list/the human animations so here we go):
First: Standing perfectly still facing all the different directions, unarmed, unit's left arm.
Second: The same, except right arm.
Third (the one which were two frames "off"): Looks to me like the unit's Left arm, unarmed, movement animation. As it's a movement animation it should be for a direction - Might be the "northern" one going with the clock-wise fit for the torso order.
Fourth: Which should make this the same except for the right arm.
Fifth: Left arm, NE side-view movement animation (fitting with the clockwise order)
Sixth: Right arm, NE side-view movement animation
Seventh and Eight looks like the Eastern movement animation.
Ninth and Tenth: SE movement animation "front".
Followed by the same for the remaining directions, S: 11, 12, SW: 13, 14, W: 15, 16 and NW: 17 & 18 sets.
Which should make the last arm sets the weapon holding arms. The first set, 19 looks to be holding a one-handed weapon and set 20 is for rifles and other two-handed weapons.
Looks to fit your list perfectly.
Is that correct?
Hmm, when I think about it the only reason the game keeps the sprites chopped up like this is to save room (for what was then very premium space).
There shouldn't be a reason why we couldn't just mash the bodyparts together like in my "work sheets" for OpenXcom and have the game just replace the whole model inbetween movement animations (in effect achieving the same result as the original). Would save a lot of time when making new sprites in the future, dunno about you guys but when making completely new stuff, being able to see the "whole" and compare it to other models at the same time is a lot easier than staring at each individual part in GIMP and keeping track of 260 different layers or have a whole bunch of different files
I mean, that way fine for just modifying stuff that's already in the game. Perhaps an option (a txt file flag in the graphics file pack or something) to have the game switch between reading a set of graphics in the two ways to give more leeway. Just a thought.