Advanced Feat: Furious Focus

This tutorial assumes you've gone through Adding a Feat and Skald's Vigor, or are familiar with the basics of adding a feat and using BPCore.

We'll be adding Furious Focus.

Go through the basic setup steps:

1. Create the FuriousFocus class
2. Create the Configure method
3. Create the feat, setting the name and description

public class FuriousFocus
{
  public static void Configure()
  {
    FeatureConfigurator.New(FeatName, FeatGuid, FeatureGroup.Feat, FeatureGroup.CombatFeat)
      .SetDisplayName(FeatDisplayName)
      .SetDescription(FeatDescription)
      .Configure();
  }
}

Make sure to add FeatDisplayName and FeatDescription to your LocalizedStrings.json file.

Add the Prerequisites

Furious Focus requires Strength 13, Power Attack, and BAB +1. You might be tempted to just make Power Attack a prerequisite since it requires Strength 13 and BAB +1, but this doesn't guarantee a character meets the requirements since Power Attack may be granted as a bonus that bypasses prerequisites:

FeatureConfigurator.New(FeatName, FeatGuid, FeatureGroup.Feat, FeatureGroup.CombatFeat)
  .SetDisplayName(FeatDisplayName)
  .SetDescription(FeatDescription)
  .AddPrerequisiteStatValue(StatType.Strength, 13)
  .AddPrerequisiteStatValue(StatType.BaseAttackBonus, 1)
  .AddPrerequisiteFeature(FeatureRefs.PowerAttackFeature.ToString())
  .Configure();

Add the Attack Bonus

Furious Focus only modifies the character's attack bonus when Power Attack is active. If you look at Power Attack's blueprint it adds the PowerAttackToggleAbility which applies PowerAttackBuff, which applies a penalty using WeaponParametersAttackBonus.

Unfortunately WeaponParametersAttackBonus cannot implement Furious Focus. In fact, there are no components that support the necessary configuration to apply the bonus:

• Power Attack is active
• First attack of the turn
• Two-handed weapons only

This means we need a custom component:

[TypeId("5767d0d5-d84c-4949-94aa-e654febc3b0f")]
private class FuriousFocusBonus :
  UnitFactComponentDelegate,
  IInitiatorRulebookHandler<RuleCalculateAttackBonusWithoutTarget>
{
  public void OnEventAboutToTrigger(RuleCalculateAttackBonusWithoutTarget evt) { }

  public void OnEventDidTrigger(RuleCalculateAttackBonusWithoutTarget evt)
  {

  }
}

The TypeId attribute is not strictly necessary but is good practice. It ensures a unique type ID for your component, used when serialized to JSON. The component inherits from UnitFactComponentDelegate and IInitiatorRulebookHandler<RuleCalculateAttackBonusWithoutTarget> to mimic WeaponParametersAttackBonus.

The implementation goes in OnEventDidTrigger because the penalty from power attack is applied in OnEventAboutToTrigger. This enables applying a bonus only if power attack applies a penalty:

var powerAttackModifier =
  evt.m_ModifiableBonus?.Modifiers?
    .Where(m => m.Fact?.Blueprint == BuffRefs.PowerAttackBuff.Reference.Get())
    .Select(m => (Modifier?)m) // Cast to avoid getting a default struct
    .FirstOrDefault();
if (powerAttackModifier is null)
{
  Logger.Verbose("Skipped: power attack not applied");
  return;
}

Logger.Info($"Adding attack bonus to {Owner.CharacterName}'s attack");
evt.AddModifier(-powerAttackModifier.Value.Value, Fact, ModifierDescriptor.UntypedStackable);

To understand where this code comes from just look at how WeaponParametersAttackBonus applies its penalty. Each modifier is added to m_ModifiableBonus and includes a value and a Fact which points to the fact providing the bonus. When adding the Furious Focus bonus the Fact from UnitFactComponentDelegate is provided to ensure it shows up in the tooltips.

Add the component to the feature:

FeatureConfigurator.New(FeatName, FeatGuid, FeatureGroup.Feat, FeatureGroup.CombatFeat)
  .SetDisplayName(FeatDisplayName)
  .SetDescription(FeatDescription)
  .AddPrerequisiteStatValue(StatType.Strength, 13)
  .AddPrerequisiteStatValue(StatType.BaseAttackBonus, 1)
  .AddPrerequisiteFeature(FeatureRefs.PowerAttackFeature.ToString())
  .AddComponent<FuriousFocusBonus>()
  .Configure();

Test it out and you should see something like this:

You might notice something wrong: the bonus doesn't add up! The problem is in our use of AddModifier():

evt.AddModifier(-powerAttackModifier.Value.Value, Fact, ModifierDescriptor.UntypedStackable);

The behavior of this is different if called in OnEventDidTrigger than in OnEventAboutToTrigger. In OnEventAboutToTrigger the result has not been calculated yet, which is why we can't tell that Power Attack applies. At that point calling AddModifier() adds to the bonuses used in the event to calculate evt.Result.

However, calling AddModifier() in OnEventDidTrigger only affects the tooltip. The result is already calculated and stored in evt.Result, so to fix it modify the result directly:

evt.AddModifier(-powerAttackModifier.Value.Value, Fact, ModifierDescriptor.UntypedStackable);
evt.Result -= powerAttackModifier.Value.Value;

You still need to call AddModifier or it won't show up on the tooltip, but test again and the numbers should add up.

Completing the Feat

Right now the attack bonus eliminates the penalty from Power Attack at all times. Finishing the feat requires adding some restrictions to the bonus:

1. Two-handed weapons only
2. First attack only

These are left as an exercise. One solution is available in the "Solutions" folder if you're stuck or want to compare.

Tips:

• Look at how WeaponParametersAttackBonus supports OnlyTwoHanded
• Look at RuleAttackWithWeapon