oracle-of-secrets/Docs/Overlord.md

Overlord Sprite Analysis

This document provides an analysis of the "Overlord" sprite system, which is a special type of sprite that acts as a controller for spawning other sprites or triggering events within a room. The main logic is found in Sprites/overlord.asm.

Overview

Overlord sprites are invisible, non-interactive sprites that are placed in a room via a level editor. Their purpose is to run logic in the background, often tied to room-specific events or conditions. They are distinct from standard sprites and are processed by a separate loop.

In this project, the primary use of the Overlord system is to dynamically spawn soldiers in Hyrule Castle after the player acquires the Master Sword.

overlord.asm Analysis

• File: Sprites/overlord.asm
• Summary: This file contains the logic for Overlord04, which is hooked into the game at $09B7AE. This specific overlord is responsible for continuously spawning soldiers in Hyrule Castle to create a sense of alarm and danger.

Key Logic

• Overlord_KalyxoCastleGuards: This is the main entry point for the overlord's logic. It is a simple routine that calls SummonGuards.

• SummonGuards:

  • Trigger Condition: This routine first checks if Link has the Master Sword (LDA.l Sword : CMP.b #$02). It will only proceed if the sword level is 2 or greater.
  • Spawning Logic: If the condition is met, it calls Overlord_SpawnSoldierPath.

• Overlord_SpawnSoldierPath:

  • Spawn Timer: This routine uses OverlordTimerB as a countdown timer to manage the rate of spawning. It will not spawn a new soldier until the timer reaches zero.
  • Sprite Limit: It checks the number of active soldiers (Sprite Type $41) on screen. If there are already 5 or more, it will not spawn a new one.
  • Spawning: If the conditions are met, it calls Sprite_SpawnDynamically_slot_limited to create a new Blue Soldier ($41).
  • Positioning: The new soldier's position and initial direction are determined by data tables within the routine (soldier_position_x, soldier_position_y, soldier_direction), allowing for multiple spawn points.