Doom's Enemy AI and Behavior

Introduction

• Doom's monsters are simple: approach and attack the player, take damage, and die.
• Despite their simplicity, their behavior is quite elegant.

Monster Definitions

• Hard-coded in the engine:
  • Collection of data containing indices to various enemy states:
    • Spawn state: When idle.
    • See state: When chasing a target.
    • Pain state: When they play a pain animation and sound.
    • Melee state: For melee attacks.
    • Missile state: For ranged attacks.
    • Death state: Death animation and sound.
    • Ex-death state: Extreme death animation.
    • Raise state: Animation when resurrected.
• Example: Revenant
  • Spawn state index: s_skel_stand
  • Function: A_Look - constantly checking for player sounds and positions.

Nightmare Difficulty Differences

• Reaction time: Always starts at 8 unless it's Nightmare difficulty.
• Nightmare Mechanics:
  • Faster reaction times.
  • Faster enemy speeds: Turbo pinkies, faster projectiles.
  • Different attack patterns.

Enemy Wake-up Mechanism

• Enemies wake up by checking for player sounds in sectors.
• Ambush flag: Keeps enemies idle despite hearing sounds.
• P_LookForPlayers: Scans if players are alive and in sight.

Enemy Chasing Behavior

• See state: Defines enemy chasing behavior using A_Chase function.
  • Update angle and direction.
  • Check for melee attacks if within 64 units.
  • Attempt ranged attacks if conditions are met.
• Movement Mechanics:
  • Use P_NewChaseDir: Calculates shortest path to the player.
  • Bumping into obstacles leads to recalculating path.

Attacking Behavior

• Melee Attack: Perform if player is within range.
• Missile Attack: Conditions for ranged attacks, e.g., line of sight, distance.
• Reaction to Pain: Counter with projectile attacks.

Damage and Death Mechanics

• When harmed: Calls P_DamageMobj function.
  • Lost Souls reset momentum.
  • Pain states activate based on pain chances.
• When health drops to zero: Calls P_KillMobj.
  • Checks whether to play death or ex-death animation.
  • Boss death triggers special actions.

Resurrection and Wake-up

• Corpse respawn on lighter difficulties if certain conditions are met.
• Arch-vile resurrection involves reversing death animation.

Lost Souls Specifics

• No wake-up sound.
• Spawn limit of 21 to prevent overload.
• Unique physics during charging and collision.

Conclusion

• Comprehensive overview of Doom's enemy behavior.
• Acknowledgments to various supporters and contributors.