Computed Stats

This guide covers computed stats - a scripting feature for dynamic stat calculations. If you're new to characters in Dryad Engine, start with Overview first.

In the basic character system, stats simply add up. If your template gives +100 Health and an item gives +20 Health, you have 120 Health. Simple addition.

But what if you need stats that depend on something else entirely?

Examples:

• Endurance stat gives +10 Stamina per point
• A global "difficulty" property affects all characters' defense
• Having 3+ equipped items from the same set gives a bonus
• Party size affects individual character stats

This is what computed stats are for - stats calculated dynamically from any game data.

Why Use Computed Stats?

Computed stats let you create relationships that simple addition can't handle:

• Derived stats - Endurance gives Stamina, Intelligence gives Mana
• Global modifiers - A "world danger" property affects all combat stats
• Set bonuses - Equipping multiple items from a set grants extra stats
• Conditional bonuses - Stats that depend on character state, attributes, or traits
• Cross-character effects - Party composition affecting individual stats

What You Can Access

Your computed stat function receives the character, but you can access anything in the game:

From the Character:

• character.getStat(name) - other stats
• character.getTrait(key) - character traits
• character.getAttribute(key) - character attributes
• character.getEquippedItems() - equipped items
• character.learnedSkills - learned skills
• character.statuses - active status effects

From game:

• game.getProperty(id) - global properties
• game.getState(key) - global game state
• game.getStore(id) - custom stores
• game.getAllCharacters() - all characters
• game.getParty() - party members

All game data is reactive - when the underlying data changes, computed stats automatically recalculate.

How They Work

Computed stats have two parts:

1. A stat computer function (defined in your game's script)

game.registerStatComputer("myComputer", (character) => {
  // Access any game data here
  // Return stat bonuses as { statName: amount }
  return {
    health: 50,
    stamina: 20
  };
});

2. A reference in the template or status (in the editor)

In the Character Templates or Character Statuses form, add the computer's name to the computed_stats field:

computed_stats: ["myComputer"]

Examples

Example 1: Stat to Stat

Every point of Endurance gives +10 Stamina:

game.registerStatComputer("enduranceToStamina", (character) => {
  const endurance = character.getStat("endurance") || 0;
  return {
    stamina: endurance * 10
  };
});

Example 2: Global Property to Stat

A global "difficulty" property affects all characters' defense:

game.registerStatComputer("difficultyPenalty", (character) => {
  const difficulty = Number(game.getProperty("difficulty")?.currentValue) || 1;
  return {
    defense: -10 * (difficulty - 1)  // Higher difficulty = less defense
  };
});

Example 3: Equipped Items (Set Bonus)

Count equipped items with a specific trait for a set bonus:

game.registerStatComputer("armorSetBonus", (character) => {
  const equipped = character.getEquippedItems();
  const setPieces = equipped.filter(item =>
    item.getTrait("item_set") === "dragon_armor"
  ).length;

  // 3+ pieces = full bonus
  if (setPieces >= 3) {
    return { defense: 50, fire_resistance: 30 };
  }
  // 2 pieces = partial bonus
  if (setPieces >= 2) {
    return { defense: 20 };
  }
  return {};
});

Example 4: Multiple Sources Combined

Combine character stats with global properties:

game.registerStatComputer("combatPower", (character) => {
  const strength = character.getStat("strength") || 0;
  const worldBonus = Number(game.getProperty("combat_bonus")?.currentValue) || 0;

  return {
    attack: (strength * 2) + worldBonus
  };
});

Step-by-Step: Adding a Computed Stat

Step 1: Register the computer in your game script

game.registerStatComputer("enduranceToStamina", (character) => {
  const endurance = character.getStat("endurance") || 0;
  return {
    stamina: endurance * 10
  };
});

Step 2: Add to template or status

In Characters → Character Templates, add to computed_stats:

computed_stats: ["enduranceToStamina"]

Result: Characters with this template now get +10 Stamina per point of Endurance, updating automatically when Endurance changes.

Important Notes

Return only what changes - Your function should return only the stats you want to add. Return an empty object {} if no bonus applies.

Results are cached - Results are cached and only recalculate when dependencies change - not on every access.

Order matters - Computed stats are calculated in order. If one depends on another's result, list dependencies first.

Works with statuses too - Add computed_stats to any status(remember everything is a status, including items and skills) for temporary computed bonuses. A buff could add a relationship that disappears when the buff ends.