oracle-of-secrets/Docs/Sprites/NPCs/EonZora.md

Eon Zora

Overview

The Eon Zora is an NPC (Non-Player Character) sprite found in the Eon Abyss. Its behavior is characterized by random movement and context-sensitive dialogue that changes based on Link's current location within the game world.

Sprite Properties

Explicit sprite properties (!SPRID, !NbrTiles, etc.) are not defined within this file. It is assumed that these properties are either inherited from a vanilla sprite ID or defined in a separate configuration file, as this file focuses on the sprite's behavior and drawing.

Main Logic (Sprite_EonZora_Main)

This routine is the main entry point for the Eon Zora, executed every frame. It orchestrates the Zora's dialogue, movement, and animation.

• Dialogue: Calls EonZora_HandleDialogue to manage interactions with the player.
• Movement: Calls EonZora_Walk for random movement, followed by JSL Sprite_Move and JSL Sprite_BounceFromTileCollision for physical movement and collision handling.
• Directional Animations: Uses a jump table to play specific animations based on the Zora's current direction (Forward, Left, Right, Back).

Sprite_EonZora_Main:
{
  JSR EonZora_HandleDialogue
  JSR EonZora_Walk

  JSL Sprite_Move
  JSL Sprite_BounceFromTileCollision

  LDA.w SprAction, X
  JSL JumpTableLocal

  dw EonZora_Forward
  dw EonZora_Left
  dw EonZora_Right
  dw EonZora_Back

  EonZora_Forward:
    %PlayAnimation(0,1,10)
    RTS
  EonZora_Left:
    %PlayAnimation(2,3,10)
    RTS
  EonZora_Right:
    %PlayAnimation(4,5,10)
    RTS
  EonZora_Back:
    %PlayAnimation(6,7,10)
    RTS
}

Movement Routine (EonZora_Walk)

This routine controls the Eon Zora's random walking behavior. It uses a timer (SprTimerA, X) to periodically select a new random direction and update the sprite's SprXSpeed, X and SprYSpeed, X.

EonZora_Walk:
{
  LDA.w SprTimerA, X : BNE +
    JSL GetRandomInt : AND.b #$03 : STA.w SprAction, X : TAY
    LDA.w .speed_x, Y : STA.w SprXSpeed, X
    LDA.w .speed_y, Y : STA.w SprYSpeed, X
    LDA.b #$6A : STA.w SprTimerA, X
  +
  RTS

  .speed_x
  db 0, -4, 4, 0
  .speed_y
  db 4, 0, 0, -4
}

Dialogue Handling (EonZora_HandleDialogue)

This routine manages the Eon Zora's dialogue, which is context-sensitive based on Link's current AreaIndex. It checks for specific AreaIndex values to display tailored messages. If no specific area matches, a default message is displayed, and interacting with it can randomly set the FOUNDRINGS global variable.

EonZora_HandleDialogue:
{
  LDA.w AreaIndex : CMP.b #$63 : BNE .not_wisdom
    %ShowSolicitedMessage($01AC)
    JMP ++
  .not_wisdom
  CMP.b #$5B : BNE .not_power
    %ShowSolicitedMessage($01AB)
    JMP ++
  .not_power
  CMP.b #$40 : BNE .not_pyramid
    %ShowSolicitedMessage($01AA)
    JMP ++
  .not_pyramid
  CMP.b #$70 : BNE .not_underwater
    %ShowSolicitedMessage($01AD)
    JMP ++
  .not_underwater
  CMP.b #$42 : BNE .not_portal
    %ShowSolicitedMessage($01AF)
    JMP ++
  .not_portal
  %ShowSolicitedMessage($01AE) : BCC .no_talk
    JSL GetRandomInt : AND.b #$06 : STA.l FOUNDRINGS
  .no_talk
  ++
  RTS
}

Drawing (Sprite_EonZora_Draw)

The drawing routine handles OAM allocation and animation. It explicitly uses REP #$20 and SEP #$20 for 16-bit coordinate calculations, ensuring accurate sprite rendering.

Sprite_EonZora_Draw:
{
  JSL Sprite_PrepOamCoord
  JSL Sprite_OAM_AllocateDeferToPlayer

  LDA.w SprFrame, X : TAY ;Animation Frame
  LDA .start_index, Y : STA $06

  PHX
  LDX .nbr_of_tiles, Y ;amount of tiles -1
  LDY.b #$00
  .nextTile

  PHX ; Save current Tile Index?
  TXA : CLC : ADC $06 ; Add Animation Index Offset

  PHA ; Keep the value with animation index offset?

  ASL A : TAX

  REP #$20

  LDA $00 : CLC : ADC .x_offsets, X : STA ($90), Y
  AND.w #$0100 : STA $0E
  INY
  LDA $02 : CLC : ADC .y_offsets, X : STA ($90), Y
  CLC : ADC #$0010 : CMP.w #$0100
  SEP #$20
  BCC .on_screen_y

  LDA.b #$F0 : STA ($90), Y ;Put the sprite out of the way
  STA $0E
  .on_screen_y

  PLX ; Pullback Animation Index Offset (without the *2 not 16bit anymore)
  INY
  LDA .chr, X : STA ($90), Y
  INY
  LDA .properties, X : STA ($90), Y

  PHY
  TYA : LSR #2 : TAY
  LDA .sizes, X : ORA $0F : STA ($92), Y ; store size in oam buffer
  PLY : INY
  PLX : DEX : BPL .nextTile

  PLX

  RTS

  .start_index
  db $00, $02, $04, $06, $08, $0A, $0C, $0D
  .nbr_of_tiles
  db 1, 1, 1, 1, 1, 1, 0, 0
  .x_offsets
  dw 0, 16
  dw 0, -16
  dw 0, 8
  dw 0, 8
  dw 0, -8
  dw 0, -8
  dw 0
  dw 0
  .y_offsets
  dw 0, 0
  dw 0, 0
  dw 0, 0
  dw 0, 0
  dw 0, 0
  dw 0, 0
  dw 0
  dw 0
  .chr
  db $60, $62
  db $60, $62
  db $40, $41
  db $43, $44
  db $40, $41
  db $43, $44
  db $64
  db $64
  .properties
  db $39, $39
  db $79, $79
  db $39, $39
  db $39, $39
  db $79, $79
  db $79, $79
  db $39
  db $79
  .sizes
  db $02, $02
  db $02, $02
  db $02, $02
  db $02, $02
  db $02, $02
  db $02, $02
  db $02
  db $02
}

Design Patterns

• Context-Sensitive Dialogue: The NPC's dialogue dynamically changes based on Link's current AreaIndex, providing a rich and immersive storytelling experience tailored to the player's location.
• Random Movement: The Zora exhibits random walking behavior, contributing to the environmental ambiance and making the world feel more alive.
• NPC Interaction: Provides dialogue and has the potential to grant items (randomly setting FOUNDRINGS), adding an element of surprise and reward to player interactions.
• Animation-Driven Movement: The sprite's movement states are directly tied to specific animations for each direction, ensuring visual consistency between its actions and appearance.
• 16-bit OAM Calculations: Demonstrates explicit use of REP #$20 and SEP #$20 for precise 16-bit OAM coordinate calculations, crucial for accurate sprite rendering.