oracle-of-secrets/Docs/Sprites/Objects/SwitchTrack.md

Switch Track

Overview

The Switch Track sprite (!SPRID = Sprite_SwitchTrack) is an interactive object designed to function as a rotating segment of a minecart track. Its visual appearance and implied path change dynamically based on its SprAction (which represents its mode of rotation) and the on/off state of a corresponding switch, stored in SwitchRam.

Sprite Properties

• !SPRID: Sprite_SwitchTrack (Custom symbol, likely a remapped vanilla ID)
• !NbrTiles: 02
• !Harmless: 00
• !HVelocity: 00
• !Health: 01
• !Damage: 00
• !DeathAnimation: 00
• !ImperviousAll: 00
• !SmallShadow: 00
• !Shadow: 00
• !Palette: 00
• !Hitbox: 00
• !Persist: 01 (Continues to live off-screen)
• !Statis: 00
• !CollisionLayer: 00
• !CanFall: 00
• !DeflectArrow: 00
• !WaterSprite: 00
• !Blockable: 00
• !Prize: 00
• !Sound: 00
• !Interaction: 00
• !Statue: 00
• !DeflectProjectiles: 00
• !ImperviousArrow: 00
• !ImpervSwordHammer: 00
• !Boss: 00

Main Structure (Sprite_RotatingTrack_Long)

This routine handles the Switch Track's drawing and dispatches to its main logic if the sprite is active.

Sprite_RotatingTrack_Long:
{
  PHB : PHK : PLB
  JSR Sprite_RotatingTrack_Draw
  JSL Sprite_CheckActive : BCC .SpriteIsNotActive
    JSR Sprite_RotatingTrack_Main
  .SpriteIsNotActive
  PLB
  RTL
}

Initialization (Sprite_RotatingTrack_Prep)

This routine initializes the Switch Track upon spawning. It sets SprDefl, X to $80. It then calculates the tile attributes of the tile directly above the switch track and sets SprAction, X based on the SPRTILE value (normalized by subtracting $D0). This SprAction, X likely determines the initial mode or orientation of the track.

Sprite_RotatingTrack_Prep:
{
  PHB : PHK : PLB
  LDA.b #$80 : STA.w SprDefl, X

  ; Setup Minecart position to look for tile IDs
  ; We use AND #$F8 to clamp to a 8x8 grid.
  ; Subtract 8 from the Y position to get the tile right above instead.
  LDA.w SprY, X : AND #$F8 : SEC : SBC.b #$08 : STA.b $00
  LDA.w SprYH, X : STA.b $01

  LDA.w SprX, X : AND #$F8 : STA.b $02
  LDA.w SprXH, X : STA.b $03

  ; Fetch tile attributes based on current coordinates
  LDA.b #$00 : JSL Sprite_GetTileAttr

  LDA.w SPRTILE : SEC : SBC.b #$D0 : STA.w SprAction, X

  PLB
  RTL
}

Constants

• SwitchRam = $0230: A WRAM address that stores the state (on/off) of each individual switch, indexed by its SprSubtype. This allows for multiple independent switch tracks.

Main Logic & State Machine (Sprite_RotatingTrack_Main)

This routine manages the visual state of the Switch Track based on its SprAction (mode of rotation) and the corresponding switch state in SwitchRam.

• Modes: The SprAction, X determines the mode of rotation, with four defined modes:
  • 0 = TopLeft -> TopRight
  • 1 = BottomLeft -> TopLeft
  • 2 = TopRight -> BottomRight
  • 3 = BottomRight -> BottomLeft
• State-Based Animation: For each mode, the SprFrame, X (animation frame) is set based on the on/off state of the switch (SwitchRam, Y). This visually changes the track's orientation.

Sprite_RotatingTrack_Main:
{
  ; Get the subtype of the track so that we can get its on/off state.
  LDA.w SprSubtype, X : TAY

  LDA.w SprAction, X
  JSL UseImplicitRegIndexedLocalJumpTable

  dw TopLeftToTopRight
  dw BottomLeftToTopLeft
  dw TopRightToBottomRight
  dw BottomRightToBottomLeft

  ; 00 = TopLeft -> TopRight
  TopLeftToTopRight:
  {
    LDA.w SwitchRam, Y : BNE .part2
      LDA.b #$00 : STA.w SprFrame, X
      RTS
    .part2
    LDA.b #$01 : STA.w SprFrame, X
    RTS
  }

  ; 01 = BottomLeft -> TopLeft
  BottomLeftToTopLeft:
  {
    LDA.w SwitchRam, Y : BNE .part2_c
      LDA.b #$03 : STA.w SprFrame, X
      RTS
    .part2_c
    LDA.b #$00 : STA.w SprFrame, X
    RTS
  }

  ; 02 = TopRight -> BottomRight
  TopRightToBottomRight:
  {
    LDA.w SwitchRam, Y : BNE .part2_a
      LDA.b #$01 : STA.w SprFrame, X
      RTS
    .part2_a
    LDA.b #$02 : STA.w SprFrame, X
    RTS
  }

  ; 03 = BottomRight -> BottomLeft
  BottomRightToBottomLeft:
  {
    LDA.w SwitchRam, Y : BEQ .part2_b
      LDA.b #$03 : STA.w SprFrame, X
      RTS
    .part2_b
    LDA.b #$02 : STA.w SprFrame, X
    RTS
  }
}

Drawing (Sprite_RotatingTrack_Draw)

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

Sprite_RotatingTrack_Draw:
{
  JSL Sprite_PrepOamCoord
  LDA.b #$04 : JSL OAM_AllocateFromRegionB

  LDA $0DC0, X : CLC : ADC $0D90, 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 : STA ($90), Y
  AND.w #$0100 : STA $0E
  INY
  LDA $02 : 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.b #$02 : ORA $0F : STA ($92), Y ; store size in oam buffer

  PLY : INY

  PLX : DEX : BPL .nextTile

  PLX

  RTS

  .start_index
    db $00, $01, $02, $03
  .nbr_of_tiles
    db 0, 0, 0, 0
  .chr
    db $44
    db $44
    db $44
    db $44
  .properties
    db $3D
    db $7D
    db $FD
    db $BD
}

Design Patterns

• Interactive Puzzle Element: The Switch Track is a key puzzle element that changes its orientation based on an external switch (likely the mineswitch sprite), directly influencing the path of minecarts.
• State-Based Animation: The track's animation frame (SprFrame, X) is directly controlled by the on/off state of a corresponding switch in SwitchRam, providing clear visual feedback to the player about its current configuration.
• Subtype-Driven State: The SprSubtype is used to index into SwitchRam, allowing each individual Switch Track to maintain its own independent state. This enables complex puzzle designs with multiple, distinct switch tracks.
• 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.