aede7551a3
- Created detailed documentation for the Minecart sprite, outlining its properties, constants, collision setup, main logic, and design patterns. - Added documentation for the Pedestal sprite, including its vanilla overrides, custom logic for item interaction, and event triggering based on area context. - Introduced documentation for the Portal sprite, detailing its two-way warping system, initialization, main logic, and helper routines for seamless transitions. - Documented the Switch Track sprite, explaining its interactive behavior, state-based animation, and integration with external switches for dynamic track manipulation.
314 lines
10 KiB
Markdown
314 lines
10 KiB
Markdown
# Thunder Ghost Sprite Analysis
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This document provides a detailed analysis of the `thunder_ghost.asm` sprite, outlining its properties, core routines, and behavioral patterns.
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## 1. Sprite Properties
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The following `!SPRID` constants define Thunder Ghost's fundamental characteristics:
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```asm
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!SPRID = Sprite_ThunderGhost
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!NbrTiles = 03 ; Number of tiles used in a frame
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!Harmless = 00 ; 00 = Sprite is Harmful, 01 = Sprite is Harmless
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!HVelocity = 00 ; Is your sprite going super fast? put 01 if it is
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!Health = 10 ; Number of Health the sprite have (dynamically set in _Prep)
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!Damage = 00 ; (08 is a whole heart), 04 is half heart
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!DeathAnimation = 00 ; 00 = normal death, 01 = no death animation
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!ImperviousAll = 00 ; 00 = Can be attack, 01 = attack will clink on it
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!SmallShadow = 00 ; 01 = small shadow, 00 = no shadow
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!Shadow = 00 ; 00 = don't draw shadow, 01 = draw a shadow
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!Palette = 00 ; Unused in this template (can be 0 to 7)
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!Hitbox = 09 ; 00 to 31, can be viewed in sprite draw tool
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!Persist = 00 ; 01 = your sprite continue to live offscreen
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!Statis = 00 ; 00 = is sprite is alive?, (kill all enemies room)
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!CollisionLayer = 00 ; 01 = will check both layer for collision
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!CanFall = 00 ; 01 sprite can fall in hole, 01 = can't fall
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!DeflectArrow = 00 ; 01 = deflect arrows
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!WaterSprite = 00 ; 01 = can only walk shallow water
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!Blockable = 00 ; 01 = can be blocked by link's shield?
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!Prize = 00 ; 00-15 = the prize pack the sprite will drop from
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!Sound = 00 ; 01 = Play different sound when taking damage
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!Interaction = 00 ; ?? No documentation
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!Statue = 00 ; 01 = Sprite is statue
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!DeflectProjectiles = 00 ; 01 = Sprite will deflect ALL projectiles
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!ImperviousArrow = 00 ; 01 = Impervious to arrows
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!ImpervSwordHammer = 00 ; 01 = Impervious to sword and hammer attacks
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!Boss = 00 ; 00 = normal sprite, 01 = sprite is a boss
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```
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**Note:** `!Health` is initially set to `10` but is dynamically determined during initialization based on Link's sword level.
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## 2. Core Routines
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### 2.1. `Sprite_ThunderGhost_Long` (Main Loop)
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This is the primary entry point for Thunder Ghost's per-frame execution. It handles drawing, shadow rendering (conditionally), and then dispatches to the main logic routine if the sprite is active.
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```asm
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Sprite_ThunderGhost_Long:
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{
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PHB : PHK : PLB
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JSR Sprite_ThunderGhost_Draw
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LDA.w SprAction, X : CMP.b #$03 : BCS + ; Don't draw shadow if casting thunder
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JSL Sprite_DrawShadow
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+
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JSL Sprite_CheckActive : BCC .SpriteIsNotActive
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JSR Sprite_ThunderGhost_Main
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.SpriteIsNotActive
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PLB
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RTL
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}
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```
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### 2.2. `Sprite_ThunderGhost_Prep` (Initialization)
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This routine is executed once when Thunder Ghost is first spawned. It sets its health based on Link's sword level and initializes `SprTimerA` and `SprTimerB`.
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```asm
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Sprite_ThunderGhost_Prep:
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{
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PHB : PHK : PLB
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LDA.l Sword : DEC A : TAY
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LDA.w .health, Y : STA.w SprHealth, X ; Set health based on sword level
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LDA.b #$08 : STA.w SprTimerB, X
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LDA.b #$08 : STA.w SprTimerA, X
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PLB
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RTL
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.health
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db $06, $0A, $0C, $10 ; Health values for each sword level
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}
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```
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### 2.3. `Sprite_ThunderGhost_Main` (Behavioral State Machine)
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This routine manages Thunder Ghost's AI through a state machine, using `SprAction, X` to determine its current behavior. It includes states for facing forward, left, and right, as well as states for casting thunder in different directions.
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```asm
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Sprite_ThunderGhost_Main:
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{
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%SpriteJumpTable(ThunderGhostFaceForward,
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ThunderGhostLeft,
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ThunderGhostRight,
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CastThunderLeft,
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CastThunderRight)
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ThunderGhostFaceForward:
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{
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%PlayAnimation(0, 1, 16)
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JSR Sprite_ThunderGhost_Move
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RTS
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}
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ThunderGhostLeft:
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{
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%PlayAnimation(2, 3, 16)
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JSR Sprite_ThunderGhost_Move
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RTS
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}
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ThunderGhostRight:
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{
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%PlayAnimation(4, 5, 16)
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JSR Sprite_ThunderGhost_Move
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RTS
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}
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CastThunderLeft:
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{
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%StartOnFrame(6)
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%PlayAnimation(6, 6, 16)
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JSL Sprite_CheckDamageToPlayer
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JSL Sprite_MoveLong
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LDA.w SprTimerA, X : BNE + ; If timer A is not 0
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STZ.w SprState, X ; Clear sprite state (despawn?)
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+
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RTS
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}
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CastThunderRight:
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{
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%StartOnFrame(6)
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%PlayAnimation(7, 7, 16)
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JSL Sprite_CheckDamageToPlayer
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JSL Sprite_MoveLong
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LDA.w SprTimerA, X : BNE + ; If timer A is not 0
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STZ.w SprState, X ; Clear sprite state (despawn?)
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+
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RTS
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}
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}
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```
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### 2.4. `Sprite_ThunderGhost_Move` (Movement and Interaction Logic)
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This routine handles Thunder Ghost's movement, collision, and interaction with the player. It also includes logic for randomly triggering lightning attacks and changing its facing direction.
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```asm
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Sprite_ThunderGhost_Move:
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{
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JSL Sprite_Move
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JSL Sprite_BounceFromTileCollision
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JSL Sprite_PlayerCantPassThrough
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JSL Sprite_DamageFlash_Long
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JSL Sprite_CheckIfRecoiling
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LDA.w SprTimerC, X : BNE ++ ; Check timer C
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JSL GetRandomInt : AND #$3F : BNE ++ ; Random chance to spawn lightning
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LDA.b #$40 : STA.w SprTimerC, X ; Set timer C
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JSR SpawnLightningAttack ; Spawn lightning attack
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++
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LDA.w SprTimerA, X : BNE + ; Check timer A
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JSL Sprite_IsToRightOfPlayer : CPY.b #$01 : BNE .ToRight ; Determine if to the right of Link
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%GotoAction(1) ; Transition to ThunderGhostLeft
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JMP .Continue
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.ToRight
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%GotoAction(2) ; Transition to ThunderGhostRight
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LDA.b #$20 : STA.w SprTimerA, X ; Set timer A
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JMP .Continue
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+
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%GotoAction(0) ; Transition to ThunderGhostFaceForward
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.Continue
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LDA.w SprMiscB, X
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JSL JumpTableLocal
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dw ThunderGhostMove
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ThunderGhostMove:
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{
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JSL GetRandomInt : AND.b #$03
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JSL Sprite_ApplySpeedTowardsPlayer
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JSL Sprite_CheckTileCollision
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JSL Sprite_CheckDamageFromPlayer
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JSL Sprite_CheckDamageToPlayer
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RTS
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}
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}
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```
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### 2.5. `SpawnLightningAttack`
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This routine is responsible for spawning the lightning attack sprite. It sets up the lightning's initial properties, including its `SprSubtype`, action, position, and speed, based on Thunder Ghost's position relative to Link.
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```asm
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SpawnLightningAttack:
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{
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PHX
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LDA.b #$CD ; Sprite ID for lightning (assuming $CD is the lightning sprite ID)
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JSL Sprite_SpawnDynamically : BMI .no_space
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; Use SprXSpeed, SprYSpeed, SprXRound, SprYRound
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; SprX, SprY, SprXH, SprY, to cast the lightning spell
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; and make it move off to the bottom left or bottom right
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; Y is the ID of the new attack sprite
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; X is the ID of the current source sprite
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; Left 0 or Right 1
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PHY
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JSL Sprite_IsToRightOfPlayer : TAY : CMP.b #$01 : BEQ + ; Determine if to the right of Link
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LDA.b #$00
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JMP .Continue
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+
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LDA.b #$01
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.Continue
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CLC : ADC.b #$03
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PLY
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STA.w SprSubtype, Y ; Set SprSubtype for lightning
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STA.w SprAction, Y ; Set action for lightning
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LDA.w SprX, X : STA.w SprX, Y
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LDA.w SprY, X : STA.w SprY, Y
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LDA.w SprXH, X : STA.w SprXH, Y
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LDA.w SprYH, X : STA.w SprYH, Y
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LDA.w SprXSpeed, X : STA.w SprXSpeed, Y
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LDA.w SprYSpeed, X : STA.w SprYSpeed, Y
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LDA.b #$02 : STA.w SprXRound, Y
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LDA.b #$02 : STA.w SprYRound, Y
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LDA.b #$30 : STA.w SprTimerA, Y
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LDA.b #$30 : STA.w SprTimerB, Y
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.no_space
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PLX
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RTS
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}
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```
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### 2.6. `Sprite_ThunderGhost_Draw` (Drawing Routine)
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This routine is responsible for rendering Thunder Ghost's graphics. It uses the `%DrawSprite()` macro, which reads from a set of data tables to handle its multi-tile appearance and animation.
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```asm
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Sprite_ThunderGhost_Draw:
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{
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%DrawSprite()
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.start_index
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db $00, $03, $06, $09, $0C, $0F, $12, $15
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.nbr_of_tiles
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db 2, 2, 2, 2, 2, 2, 2, 2
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.x_offsets
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dw 0, 0, 8
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dw 8, 0, 0
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dw 0, 0, 8
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dw 0, 0, 8
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dw 0, 8, 0
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dw 0, 8, 0
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dw -12, -8, -16
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dw 12, 16, 20
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.y_offsets
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dw -8, 0, -8
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dw -8, 0, -8
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dw 0, -8, -8
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dw 0, -8, -8
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dw 0, -8, -8
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dw 0, -8, -8
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dw 12, 24, 20
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dw 12, 24, 12
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.chr
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db $3A, $02, $3B
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db $3A, $02, $3B
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db $20, $00, $01
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db $22, $10, $11
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db $20, $00, $01
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db $22, $10, $11
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db $28, $2A, $2B
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db $28, $2A, $2B
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.properties
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db $2B, $2B, $2B
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db $6B, $6B, $6B
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db $2B, $2B, $2B
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db $2B, $2B, $2B
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db $6B, $6B, $6B
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db $6B, $6B, $6B
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db $2B, $2B, $2B
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db $6B, $2B, $2B
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.sizes
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db $00, $02, $00
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db $00, $02, $00
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db $02, $00, $00
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db $02, $00, $00
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db $02, $00, $00
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db $02, $00, $00
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db $02, $00, $00
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db $02, $00, $00
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}
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```
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## 3. Key Behaviors and Implementation Details
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* **Dynamic Health:** Thunder Ghost's health is determined at spawn time based on Link's current sword level, allowing for dynamic difficulty scaling.
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* **Conditional Shadow Drawing:** The shadow is not drawn when Thunder Ghost is in its `CastThunderLeft` or `CastThunderRight` states, suggesting a visual distinction during its attack.
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* **Lightning Attack:** Thunder Ghost has a random chance to spawn a lightning attack (`SpawnLightningAttack`) at regular intervals, which then becomes an independent sprite with its own movement and interaction logic.
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* **State Management:** Thunder Ghost uses `SprAction, X` and `%SpriteJumpTable` to manage its facing direction (forward, left, right) and its thunder-casting states.
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* **Movement Patterns:** Thunder Ghost moves randomly and applies speed towards the player, while also bouncing from tile collisions and being unable to be passed through by Link.
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* **Projectile Spawning with Directional Logic:** The `SpawnLightningAttack` routine demonstrates how to spawn a projectile (`$CD`) and initialize its properties, including its `SprSubtype` and `SprAction`, based on Thunder Ghost's position relative to Link.
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* **`SprTimerA`, `SprTimerB`, `SprTimerC` Usage:** These timers are used to control the frequency of lightning attacks and the duration of facing/movement states.
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* **`Sprite_MoveLong`:** Used in the `CastThunderLeft` and `CastThunderRight` states, suggesting a specific movement behavior during the attack animation.
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