Something causes animation order bug in explosion AOE attack (presumably reg_anim_clear)

[dekrus]

After interrupting any animations and then using an AOE explosion attack that kills some targets, 1 or more targets play their death/damage animation before the explosion animation, instead of after.
Video

Environment:
Clean Fallout 2 no mods + sfall 4.5 (also reproduced on sfall 4.4.4+ and 5+)
AllowUnsafeScripting=0 (no unsafe scripting)
Does NOT happen on vanilla Fallout 2 without sfall(in my testes)

Steps to Reproduce:

1. Load attached save
2. Spam movement to interrupt the walking animation.
3. Throw a frag grenade at a group of 2+ critters (the bug occurs on every load, usually on the 1-2 grenade).

Workaround:
Calling empty reg_anim_begin/reg_anim_end cycles in AFTERHITROLL prevents the bug:

    reg_anim_combat_check(0);
    for (i = 0; i < 7; i = i + 1) begin // less than 7 is not enough
        reg_anim_begin();
        reg_anim_end();
    end

My Thoughts:
Since the bug only occurs with sfall (not vanilla) and is fixed by 7+ empty reg_anim_begin/end cycles, the likely cause is LockAnimSlot() setting an 8-frame lock on slots after reg_anim_clear. This blocks animationRegisterPing from finding correct slots for AOE extra targets, causing death anims to fire before the explosion.

Suggested Fix:
In LockAnimSlot, skip locking when the slot is already completed:

  static long __fastcall LockAnimSlot(long slot) {
      if (slot < animationLimit 
          && animSet[slot].currentAnim != -1000  // skip finished slots
          && animSet[slot].counter != animSet[slot].totalAnimCount) 
      {
          lockAnimSet[slot] = 8;
      }
      return slot;
  }

But couldn't compile sfall locally to verify, so maybe I'm totally wrong on the cause! : )

[NovaRain]

Haven't checked your purposed fix yet. The cause seems to be the tweak that prevent the "forever" type of animation from stopping when entering combat. It shouldn't happen on sfall 4.4.3.1 or earlier, only 4.4.4+.

[dekrus]

Indeed, I couldn't reproduce it on 4.4.3.

[NovaRain]

sfall-suggested-fix.zip
Your suggested fix doesn't seem to work.
If I click movement only 3 times, the death animation still works normally, from 4 times it starts glitching.

[NovaRain]

sfall-anim-aoe-fix.zip
I fiddled around the animation code and found a possible solution. Please try this build.

[dekrus]

Tried the build. The bug is gone, everything works correctly. No other issues found so far.

What was the actual cause in the end?

[NovaRain]

When the animation temp lock got introduced, anim_stop_ calls in various places would clear all locks (anim_stop_hack). The tweak for the "forever" type of animation replaces one of the calls (combat_begin_anim_stop_hook), but it didn't include the clearing lock process as the normal anim_stop_ does. So when entering combat the locks are still in place, causing the order bug.