[Bug] Stealth detection spells without provocation

Cadros

Game Behaviour at Present

If my character sneaks up on certain enemies while invisible, as soon as my character is in range they start to cast a spell to remove invisibility.

Expected Behaviour

Most enemies would be very unlikely to be able to spot that someone invisible was approaching, and therefore I would expect that most of the time if the enemy has not yet engaged with you at any point then they would not cast invisibility removal spells.

AlexT

This is a deliberate design decision made by the original developers and not a bug. Certain characters (i.e. Perth the Adept in BG2) have been specifically scripted to exhibit this behavior. Here's an excerpt from MAGE18B.BCS:

IF
  Allegiance(Myself,ENEMY)
  Detect([PC])
  !See(LastSeenBy(Myself))
  HaveSpell(WIZARD_TRUE_SIGHT)
THEN
  RESPONSE #100
    Spell(Myself,WIZARD_TRUE_SIGHT)
END

In theory, an opponent could still hear the footsteps of your invisible character and react based on that. Ideally, there should be a Move Silently check in there to account for truly stealthy characters, but that's more along the lines of a feature request.

Cadros

I bow to your superior knowledge, and would be happy to settle for a move silently/ dexterity based check

technophobe

That happens even when it's a stealthed thief who likely won't be heard, either. Just another example of bad/lazy AI.

AlexT

That happens even when it's a stealthed thief who likely won't be heard, either. Just another example of bad/lazy AI.

That could be avoided with relative ease by changing the aforementioned block to something like this:

IF
  Allegiance(Myself,ENEMY)
  Detect([PC])
  !See(LastSeenBy(Myself))
  CheckStatLT(LastSeenBy(Myself),40,STEALTH) // Move Silently is less than 40
  !StateCheck(LastSeenBy(Myself),STATE_SILENCED) // not under a Silence spell
  HaveSpell(WIZARD_TRUE_SIGHT)
THEN
  RESPONSE #100
    Spell(Myself,WIZARD_TRUE_SIGHT)
END

Using the revised block, the opponent could not detect an invisible character with a Move Silently score of 40+ nor could he hear an invisible character affected by a Silence spell. I use similar script blocks for certain opponents in my mods.

Boaster

Yes, this is something that is ludicrous. The AI check should be more involved. Cuz you just can't sneak past a beholder.

Like, every 6 seconds there should be a check. If an invisible target is moving, do a check against stealth, move silently, dexterity and so forth. Avenger's script looks good.

Lunever

There is a bug though - a ranger's STEALTH is internally written in the character's Move Silently AND Hide in Shadows skill value (which is correct).
However, the original devs forgot to change the skills of a Thief ALSO to Stealth, a Thief only has Move Silently and an internal Hide in Shadows Skill of 0. I fixed that with Shadowkeeper after every thief level-up as a workaround so far and set HiS = MS.