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This tutorial will cover adding new collision types for spinner tiles in all four cardinal directions as well as a stopper tile to stop the player from spinning. Credit to Rangi42 for implementing this in Pokemon Polished Crystal
## Contents
1. [Create Constants for the New Collision Types](#1-create-constants-for-the-new-collision-types)
2. [Implement New Movement Functionality](#2-implement-new-movement-functionality)
3. [Prevent Oddities When Losing Battles](#3-prevent-oddities-when-losing-battles)
## 1. Create Constants for the New Collision Types
In order to add new collision types to use on maps, we'll have to define constants for them.
Edit [constants/collision_constants.asm](../blob/master/constants/collision_constants.asm)
```diff
COLL_DOOR_7D EQU $7d ; unused
COLL_WARP_CARPET_RIGHT EQU $7e
COLL_WARP_7F EQU $7f ; unused
+COLL_STOP_SPIN EQU $80
+COLL_SPIN_UP EQU $81
+COLL_SPIN_DOWN EQU $82
+COLL_SPIN_LEFT EQU $83
+COLL_SPIN_RIGHT EQU $84
COLL_COUNTER EQU $90
COLL_BOOKSHELF EQU $91
COLL_PC EQU $93
```
Edit [constants/map_object_constants.asm](../blob/master/constants/map_object_constants.asm)
```diff
const STEP_TURN ; 5
const STEP_BACK_LEDGE ; 6
const STEP_WALK_IN_PLACE ; 7
+ const STEP_SPIN ; 8
```
Edit [data/collision/collision_permissions.asm](../blob/master/data/collision/collision_permissions.asm) (data/collision_permissions.asm on older versions of pokecrystal)
```diff
db LAND_TILE ; COLL_DOOR_7D
db LAND_TILE ; COLL_WARP_CARPET_RIGHT
db LAND_TILE ; COLL_WARP_7F
- db WALL_TILE ; 80
- db WALL_TILE ; 81
- db WALL_TILE ; 82
- db WALL_TILE ; 83
- db WALL_TILE ; 84
+ db LAND_TILE ; COLL_STOP_SPIN
+ db LAND_TILE ; COLL_SPIN_UP
+ db LAND_TILE ; COLL_SPIN_DOWN
+ db LAND_TILE ; COLL_SPIN_LEFT
+ db LAND_TILE ; COLL_SPIN_RIGHT
db LAND_TILE ; 85
db LAND_TILE ; 86
db LAND_TILE ; 87
```
We'll need to add a flag in WRAM to denote whether we are currently spinning.
Edit [wram.asm](../blob/master/wram.asm)
```diff
wScrollingMenuListSize:: db
- ds 1
-
; used when following a map warp
wNextWarp:: db
wNextMapGroup:: db
...
wPlayerStepFlags:: db
wPlayerStepDirection:: db
+wSpinning:: db
+
wBGMapAnchor:: dw
UNION
```
## 2. Implement New Movement Functionality
Now that we have our constants in order, we have to add functionality specific to these tiles.
Edit [engine/overworld/player_movement.asm](../blob/master/engine/overworld/player_movement.asm)
```diff
DoPlayerMovement::
...
jr z, .bump
cp 2
jr z, .bump
+
+ ld a, [wSpinning]
+ and a
+ jr nz, .spin
ld a, [wPlayerStandingTile]
call CheckIceTile
...
xor a
ret
+.spin
+ ld de, SFX_SQUEAK
+ call PlaySFX
+ ld a, STEP_SPIN
+ call .DoStep
+ scf
+ ret
+
.bump
xor a
+ ld [wSpinning], a
ret
.TrySurf:
...
dw .TurningStep
dw .BackJumpStep
dw .FinishFacing
+ dw .SpinStep
.SlowStep:
slow_step DOWN
...
db $80 | UP
db $80 | LEFT
db $80 | RIGHT
+.SpinStep
+ turn_in_down
+ turn_in_up
+ turn_in_left
+ turn_in_right
.StandInPlace:
ld a, 0
...
.CheckForced:
-; When sliding on ice, input is forced to remain in the same direction.
+; When sliding on ice or spinning, input is forced to remain in the same direction.
+ call CheckSpinning
+ jr z, .not_spinning
+ dec a
+ jr .force
+
+.not_spinning
call CheckStandingOnIce
ret nc
...
cp 0
ret z
+.force
maskbits NUM_DIRECTIONS
ld e, a
ld d, 0
...
.not_ice
and a
ret
+CheckSpinning::
+ ld a, [wPlayerStandingTile]
+ cp COLL_STOP_SPIN
+ jr z, .stop_spin
+ call CheckSpinTile
+ jr z, .start_spin
+ ld a, [wSpinning]
+ and a
+ ret
+
+.start_spin
+ ld a, c
+ inc a
+ ld [wSpinning], a
+ and a
+ ret
+
+.stop_spin
+ xor a
+ ld [wSpinning], a
+ ret
+
+CheckSpinTile:
+ cp COLL_SPIN_UP
+ ld c, UP
+ ret z
+ cp COLL_SPIN_DOWN
+ ld c, DOWN
+ ret z
+ cp COLL_SPIN_LEFT
+ ld c, LEFT
+ ret z
+ cp COLL_SPIN_RIGHT
+ ld c, RIGHT
+ ret z
+ ld c, STANDING
+ ret
+
StopPlayerForEvent::
ld hl, wPlayerNextMovement
ld a, movement_step_sleep
```
## 3. Prevent Oddities When Losing Battles
Since it is possible for battles to begin if trainers spot you while you are spinning, a slight addition must be made to the whiteout engine event script to account for a scenario where the player would never stop spinning.
Edit [engine/events/whiteout.asm](../blob/master/engine/events/whiteout.asm)
```diff
HalveMoney:
farcall StubbedTrainerRankings_WhiteOuts
; Halve the player's money.
+ xor a
+ ld [wSpinning], a
ld hl, wMoney
ld a, [hl]
srl a
```
This edit can still be made if you've adjusted the money reduction function, just add the two new lines before loading wMoney into hl.
That's the hardest part! All that's left to do is edit blocksets as desired in Polished Map to include tiles with the types SPIN_LEFT, SPIN_UP, SPIN_DOWN, SPIN_RIGHT, and STOP_SPIN.
|
