Rules

The rules modules, imported globally as Rules, allows anyone who wishes to modify default behaviors to do so in a way that will be compatible with all other users. The only limitation is that the function signatures must remain the same.

Sections

• Abilities
• Armor Class
• Attack Bonus
• Classes
• Combat
• Combat Modifiers
• Concealment
• Constants
• Damage
• Damage Reduction
• Feats
• Hitpoints
• Immunities
• Levels
• Modes
• Races
• Saves
• Situations
• Skills
• Special Attacks
• Weapons

Examples

Replacing a function.

-- In some file that you load from your preload file.

-- Suppose you think it more appropriate to change Epic Toughness feats to grant 40hp per feat.
-- We'll leave aside whether this is a good or bad idea.

local function GetMaxHitPoints(cre)
  local res = 0
  local not_pc = cre:GetIsAI()
  local level = cre:GetHitDice()
  if cre:GetHasFeat(FEAT_TOUGHNESS) then
    res = res + level
  end

  res = res + math.max(0, cre:GetAbilityModifier(ABILITY_CONSTITUTION) * level)

  local pm = cre:GetLevelByClass(CLASS_TYPE_PALE_MASTER)
  local pmhp = 0
  if pm >= 5 then
    if pm >= 25 then
      pmhp = 18 + (math.floor(pm / 5) * 20)
    elseif pm >= 15 then
      pmhp = 18 + (math.floor(pm / 5) * 10)
    elseif pm >= 10 then
      pmhp = 18 + math.floor((pm - 10) / 5)
    else
      pmhp = pm * 3
    end
  end
  res = res + pmhp

  local epictough = cre:GetHighestFeatInRange(FEAT_EPIC_TOUGHNESS_1, FEAT_EPIC_TOUGHNESS_10)
  if epictough ~= -1 then
    -- Changed 20 -> 40.
    local et = 40 * (epictough - FEAT_EPIC_TOUGHNESS_1 + 1)
    res = res + et
  end

  -- Some of the underlying engine object is exposed here.
  -- It isn't necessary to understand this unless you have a reason
  -- to change it... and you probably shouldn't.
  if not_pc then
    res = res + cre.obj.obj.obj_hp_max
  else
    local base = 0
    for i = 1, cre:GetHitDice() do
      base = base + cre:GetMaxHitPointsByLevel(i)
    end
    res = res + base
    cre.obj.obj.obj_hp_max = res
  end

  if res <= 0 then res = 1 end

  return res
end

-- Replace the global function and now anywhere in your code
-- or in the api that calls this function will call your
-- modified version.
Rules.GetMaxHitPoints = GetMaxHitPoints

Using overrides.

A number of functions provide explicit means of overriding behaviors. In those cases it’s not necessary to replace any functions. To see examples of those checkout the sections of the rules module.