57012b2656
Add side validation to prevent players from manipulating the ice block by changing direction while in contact. Uses Sprite_DirectionToFacePlayer to verify Link's position matches his facing direction before allowing push. Key changes: - IceBlock_ValidatePushSide: Anti-cheat that validates Link is on the correct side of the block for his facing direction - Direction locking: Push direction locked in SprMiscA until block stops - Comprehensive documentation of mechanics and sprite RAM usage - Section headers for code organization 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
437 lines
12 KiB
NASM
437 lines
12 KiB
NASM
; =========================================================
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; Pushable Ice Block
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; =========================================================
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; A sliding puzzle block that Link can push in cardinal directions.
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; The block slides until it hits a wall or lands on a switch tile.
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;
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; Key Mechanics:
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; - Direction Locking: Once Link starts pushing, the direction is locked
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; in SprMiscA until the block stops moving (speed = 0).
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; - Side Validation: Link must be on the opposite side of the block from
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; the direction he's facing. Uses Sprite_DirectionToFacePlayer to
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; determine Link's relative position and validates against $26 (facing).
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; - Switch Detection: Checks center point of block against switch tiles
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; ($23, $24, $25, $3B) to stop and activate switches.
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; - Grid Snapping: Block position is snapped to 8px grid when pushed.
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;
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; Sprite RAM Usage:
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; SprMiscA - Locked push direction ($01=R, $02=L, $04=D, $08=U)
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; SprMiscC - Push state flag (set while being actively pushed)
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; SprMiscD-G - Cached initial position for damage reset
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; SprTimerA - Push momentum timer (keeps push active for 7 frames)
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; SprTimerB - Delay timer for hookshot cancellation
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; =========================================================
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!SPRID = $D5
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!NbrTiles = 02
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!Harmless = 01 ; 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 = 00 ; Number of Health the sprite have
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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 = 01 ; 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 = 01 ; 01 = Sprite is statue
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!DeflectProjectiles = 01 ; 01 = Sprite will deflect ALL projectiles
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!ImperviousArrow = 01 ; 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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%Set_Sprite_Properties(Sprite_IceBlock_Prep, Sprite_IceBlock_Long)
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; =========================================================
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; Main Entry Point - Called every frame
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; Handles push state management and dispatches to main logic
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; =========================================================
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Sprite_IceBlock_Long:
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{
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PHB : PHK : PLB
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LDA.w SprMiscC, X : BEQ .not_being_pushed
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STZ.w SprMiscC, X
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STZ.b LinkSpeedTbl
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STZ.b $48 ; Clear push actions bitfield
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.not_being_pushed
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LDA.w SprTimerA, X : BEQ .retain_momentum
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LDA.b #$01 : STA.w SprMiscC, X
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LDA.b #$84 : STA.b $48 ; Set statue and push block actions
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LDA.b #$04 : STA.b LinkSpeedTbl ; Slipping into pit speed
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.retain_momentum
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JSR Sprite_IceBlock_Draw
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JSL Sprite_CheckActive : BCC .SpriteIsNotActive
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JSR Sprite_IceBlock_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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; Initialization - Called once when sprite spawns
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; Caches initial position for damage reset
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; =========================================================
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Sprite_IceBlock_Prep:
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{
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PHB : PHK : PLB
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; Cache Sprite position
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LDA.w SprX, X : STA.w SprMiscD, X
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LDA.w SprY, X : STA.w SprMiscE, X
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LDA.w SprXH, X : STA.w SprMiscF, X
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LDA.w SprYH, X : STA.w SprMiscG, X
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STZ.w SprDefl, X
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LDA.w SprHitbox, X : ORA.b #$09 : STA.w SprHitbox, X
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PLB
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RTL
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}
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; =========================================================
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; Main Logic - Handles movement, collision, and push detection
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; =========================================================
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Sprite_IceBlock_Main:
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{
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%PlayAnimation(0, 0, 1)
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JSR Statue_BlockSprites
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JSL Sprite_CheckDamageFromPlayer : BCC .no_damage
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LDA.w SprMiscD, X : STA.w SprX, X
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LDA.w SprMiscE, X : STA.w SprY, X
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LDA.w SprMiscF, X : STA.w SprXH, X
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LDA.w SprMiscG, X : STA.w SprYH, X
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STZ.w SprXSpeed, X : STZ.w SprYSpeed, X
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STZ.w SprTimerA, X : STZ.w SprMiscA, X
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.no_damage
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STZ.w $0642
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JSR Sprite_IceBlock_CheckForSwitch : BCC .no_switch
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STZ.w SprXSpeed, X : STZ.w SprYSpeed, X
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LDA.b #$01 : STA.w $0642
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.no_switch
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JSL Sprite_Move
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JSL Sprite_Get_16_bit_Coords
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JSL Sprite_CheckTileCollision
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; ----udlr , u = up, d = down, l = left, r = right
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LDA.w SprCollision, X : AND.b #$0F : BEQ +
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; Hit a wall - clear direction only if we actually stop
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STZ.w SprMiscA, X
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+
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; If link is in contact, register a push with the sprite
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; Must be pushing from correct side for the direction
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JSL Sprite_CheckDamageToPlayerSameLayer : BCC .NotInContact
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; Check which side Link is on and validate push direction
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JSR IceBlock_ValidatePushSide : BCC .wrong_direction
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LDA.w SprMiscA, X : BNE .check_facing
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; No direction cached - lock to current facing
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LDA.b $26 : STA.w SprMiscA, X
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JSR Sprite_ApplyPush
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BRA .do_push
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.check_facing
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; Direction is locked - only allow push if Link faces same direction
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LDA.b $26 : CMP.w SprMiscA, X : BNE .wrong_direction
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.do_push
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LDA.b #$07 : STA.w SprTimerA, X
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STZ.b $5E
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JSL Sprite_RepelDash
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LDA.w SprTimerB, X : BNE .CancelHookshot
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LDA.w SprX, X : AND #$F8 : STA.w SprX, X
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LDA.w SprY, X : AND #$F8 : STA.w SprY, X
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RTS
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.CancelHookshot:
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JSL Sprite_CancelHookshot
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RTS
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.wrong_direction
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; Link is pushing from wrong side - just repel, don't move block
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JSL Sprite_RepelDash
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RTS
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.NotInContact:
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; Not in contact - only clear direction if block has stopped moving
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LDA.w SprXSpeed, X : ORA.w SprYSpeed, X : BNE .still_moving
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STZ.w SprMiscA, X ; Block stopped, allow new direction
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.still_moving
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LDA.w SprTimerA, X : BNE .delay_timer
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LDA.b #$0D : STA.w SprTimerB, X
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.delay_timer
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RTS
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}
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; =========================================================
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; Apply Push - Sets block velocity based on Link's facing direction
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; Only applies if cached direction matches current facing
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; =========================================================
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Sprite_ApplyPush:
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{
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; Only apply the push if the facing direction
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; and pushing direction agree with each other
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LDA.w SprMiscA, X : CMP.b $26 : BEQ .push
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RTS
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.push
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LDA $26 : CMP.b #$01 : BEQ .push_right
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CMP.b #$02 : BEQ .push_left
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CMP.b #$04 : BEQ .push_down
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CMP.b #$08 : BEQ .push_up
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.push_right
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LDA #16 : STA.w SprXSpeed, X : STZ.w SprYSpeed, X
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JMP +
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.push_left
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LDA #-16 : STA.w SprXSpeed, X : STZ.w SprYSpeed, X
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JMP +
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.push_down
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LDA #16 : STA.w SprYSpeed, X : STZ.w SprXSpeed, X
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JMP +
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.push_up
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LDA #-16 : STA.w SprYSpeed, X : STZ.w SprXSpeed, X
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+
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RTS
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}
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; =========================================================
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; Validate Push Side - Anti-cheat for push direction
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; =========================================================
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; Prevents players from manipulating the block by changing
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; direction while in contact. Uses Sprite_DirectionToFacePlayer
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; to determine Link's actual position relative to the block,
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; then validates that his facing direction ($26) is appropriate.
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;
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; Example: If Link is standing to the RIGHT of the block,
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; he must be facing LEFT ($02) to push it leftward.
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;
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; Returns: Carry set = valid push, Carry clear = invalid push
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; Link facing ($26): $01 = right, $02 = left, $04 = down, $08 = up
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; Sprite_DirectionToFacePlayer returns Y:
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; Y=0: Link is to the right of sprite -> must face left ($02)
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; Y=1: Link is to the left of sprite -> must face right ($01)
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; Y=2: Link is below sprite -> must face up ($08)
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; Y=3: Link is above sprite -> must face down ($04)
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; =========================================================
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IceBlock_ValidatePushSide:
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{
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JSL Sprite_DirectionToFacePlayer ; Y = Link's position relative to block
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LDA.b $26 ; A = Link's facing direction
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CPY.b #$00 : BEQ .link_is_right
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CPY.b #$01 : BEQ .link_is_left
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CPY.b #$02 : BEQ .link_is_below
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CPY.b #$03 : BEQ .link_is_above
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BRA .invalid ; Unknown direction
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.link_is_right
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CMP.b #$02 : BEQ .valid ; Must face left
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BRA .invalid
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.link_is_left
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CMP.b #$01 : BEQ .valid ; Must face right
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BRA .invalid
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.link_is_below
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CMP.b #$08 : BEQ .valid ; Must face up
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BRA .invalid
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.link_is_above
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CMP.b #$04 : BEQ .valid ; Must face down (fall through to invalid)
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.invalid
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CLC
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RTS
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.valid
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SEC
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RTS
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}
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; =========================================================
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; Helper Routines
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; =========================================================
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; Check if the tile beneath the sprite is the sliding ice
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; Currently unused as it doesnt play well with the hitbox choices
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IceBlock_CheckForGround:
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{
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LDA.w SprY, X : CLC : ADC.b #$08 : STA.b $00
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LDA.w SprYH, X : ADC.b #$00 : STA.b $01
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LDA.w SprX, X : STA.b $02
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LDA.w SprXH, X : ADC.b #$00 : STA.b $03
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LDA.w SprFloor, X
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PHY
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JSL Sprite_GetTileAttr
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PLY
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LDA.w $0FA5 : CMP.b #$0E : BNE .stop
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SEC
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RTS
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.stop
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STZ.w SprXSpeed, X
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STZ.w SprYSpeed, X
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CLC
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RTS
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}
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Sprite_IceBlock_CheckForSwitch:
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{
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; Check center point of block for switch tile
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LDA.w SprY, X : CLC : ADC.b #$08 : STA.b $00
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LDA.w SprYH, X : ADC.b #$00 : STA.b $01
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LDA.w SprX, X : CLC : ADC.b #$08 : STA.b $02
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LDA.w SprXH, X : ADC.b #$00 : STA.b $03
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LDA.w SprFloor, X
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JSL Sprite_GetTileAttr
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LDA.w $0FA5
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CMP.b #$23 : BEQ .on_switch
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CMP.b #$24 : BEQ .on_switch
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CMP.b #$25 : BEQ .on_switch
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CMP.b #$3B : BEQ .on_switch
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CLC
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RTS
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.on_switch
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SEC
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RTS
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}
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; Block other sprites from passing through this block
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; Applies recoil to sprites that collide with the ice block
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Statue_BlockSprites:
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{
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LDY.b #$0F
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.next
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; SPRITE 1C
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LDA.w SprType, Y : CMP.b #$1C : BEQ .skip
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CPY.w SprSlot : BEQ .skip
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TYA : EOR.b $1A : AND.b #$01 : BNE .skip
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LDA.w SprState, Y : CMP.b #$09 : BCC .skip
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LDA.w SprX, Y : STA.b $04
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LDA.w SprXH, Y : STA.b $05
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LDA.w SprY, Y : STA.b $06
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LDA.w SprYH, Y : STA.b $07
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REP #$20
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LDA.w SprCachedX
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SEC : SBC.b $04
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CLC : ADC.w #$000C : CMP.w #$0018 : BCS .skip
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LDA.w SprCachedY
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SEC : SBC.b $06
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CLC : ADC.w #$000C : CMP.w #$0024 : BCS .skip
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SEP #$20
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LDA.b #$04 : STA.w $0EA0, Y
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PHY
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LDA.b #$20
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JSL Sprite_CheckSlopedTileCollision ; JSR Sprite_ProjectSpeedTowardsLocation
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PLY
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LDA.b $00 : STA.w SprYRecoil, Y
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LDA.b $01 : STA.w SprXRecoil, Y
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.skip
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SEP #$20
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DEY
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BPL .next
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RTS
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}
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; =========================================================
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; Drawing - Renders the 16x16 ice block using 4 8x8 tiles
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; =========================================================
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Sprite_IceBlock_Draw:
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{
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JSL Sprite_PrepOamCoord
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JSL Sprite_OAM_AllocateDeferToPlayer
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LDA $0DC0, X : CLC : ADC.w SprFrame, X : TAY;Animation Frame
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LDA .start_index, Y : STA $06
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PHX
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LDX .nbr_of_tiles, Y ;amount of tiles -1
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LDY.b #$00
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.nextTile
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PHX ; Save current Tile Index?
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TXA : CLC : ADC $06 ; Add Animation Index Offset
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PHA ; Keep the value with animation index offset?
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ASL A : TAX
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REP #$20
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LDA $00 : CLC : ADC .x_offsets, X : STA ($90), Y
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AND.w #$0100 : STA $0E
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INY
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LDA $02 : CLC : ADC .y_offsets, X : STA ($90), Y
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CLC : ADC #$0010 : CMP.w #$0100
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SEP #$20
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BCC .on_screen_y
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LDA.b #$F0 : STA ($90), Y ;Put the sprite out of the way
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STA $0E
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.on_screen_y
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PLX ; Pullback Animation Index Offset (without the *2 not 16bit anymore)
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INY
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LDA .chr, X : STA ($90), Y
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INY
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LDA .properties, X : STA ($90), Y
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PHY
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TYA : LSR #2 : TAY
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LDA .sizes, X : ORA $0F : STA ($92), Y ; store size in oam buffer
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PLY : INY
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PLX : DEX : BPL .nextTile
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PLX
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RTS
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.start_index
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db $00
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.nbr_of_tiles
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db 3
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.x_offsets
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dw 0, 8, 0, 8
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.y_offsets
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dw 0, 0, 8, 8
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.chr
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db $E9, $E9, $E9, $E9
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.properties
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db $24, $64, $A4, $E4
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.sizes
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db $00, $00, $00, $00
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}
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