explore: rewrite as an instant screen-paging camera

Per feedback, EXPLORE should page whole screens on button presses (instant
redraw), not move/walk the character. Ripped out the walk-engine approach
entirely -- reverted the CollisionCheckOnLand noclip hook and the OverworldLoop
simulated-joypad paging hook, and removed both helpers.

EXPLORE is now a self-contained camera loop that renders straight from the map
block buffer:
  - view pointer = wOverworldMap + (by+1)*stride + bx  (LoadCurrentMapView)
  - a d-pad press shifts the camera coords by ~one screen and re-renders
  - at a map edge it crosses to the connected map using that connection's
    alignment offset (or clamps if none), LoadMapData + re-render
  - B restores the origin view + returns to the SL0P menu
No character walking, sprites hidden for a clean camera. Verified: within-map
paging steps a screen at a time, seams cross with correct offsets (Pallet ->
Route1 -> Viridian), 25-page random stress with no corruption, and normal
gameplay resumes after exit.

4 files changed, 211 insertions, 46 deletions

diff --git a/SL0P.md b/SL0P.md
index 6d02fe03..1c9da048 100644
--- a/SL0P.md
+++ b/SL0P.md
@@ -37,23 +37,25 @@ A table-driven cheat menu. Cursor + A to pick, B to back out / close.
 | **ITEMS** | submenu: give ×99 of balls, Rare Candy, Full Restore, Max Revive, Max Elixer, PP Up, and all five evolution stones |
 | **NOWILD** | toggle wild encounters off (shows `ON`) |
 | **REPEL** | refill repel steps |
-| **EXPLORE** | toggle noclip free-roam: disables collision so you (and Pikachu) walk through walls/NPCs/ledges and cross map connection seams seamlessly across the whole overworld. Pick it again to turn off. |
+| **EXPLORE** | a screen-paging overworld camera: each d-pad press instantly redraws the next screenful of the world (no walking), hopping to the connected map at each edge. B returns to the menu. |
 
 Everything is in `engine/slop_menu.asm`. Adding a new entry = add a name to
 `SlopMenuText`, a `dw Handler` to `SlopMenuHandlers`, and bump `SLOP_MENU_COUNT`.
 Handlers return carry set (a warp/exit was started) or clear (back to the menu),
 and can be submenus or one-shot actions.
 
-Persistent toggle flags: `wUnusedFlag` (NOWILD) and `wSlopNoclip` (EXPLORE, the
-repurposed unused `wUnusedObtainedBadges` at D356).
+Persistent toggle flag: `wUnusedFlag` (NOWILD).
 
-**EXPLORE / noclip** hooks the home `CollisionCheckOnLand` (5-byte early-out when
-`wSlopNoclip` is set; ROM0 room was reclaimed by deleting the unreferenced
-`Func_0db5` dead farcall in `LoadMapHeader`). The engine's own player-walk +
-connection-crossing code then carries you seamlessly across the world -- see
-`tools/render_overworld.py` for the ground-truth map that proved connections join
-maps along shared edges with an offset. (The player is left visible on purpose:
-hiding it orphaned the Pikachu follower into a lone wandering sprite.)
+**EXPLORE** is a self-contained camera loop in `engine/slop_menu.asm`. It renders
+straight out of the map block buffer (`wOverworldMap`): compute a view pointer
+`wOverworldMap + (by+1)*stride + bx` (by/bx = player block, stride = width+6),
+`LoadCurrentMapView`, push to VRAM, OBJ off. A d-pad press moves the camera coords
+by ~one screen (`SLOP_PAGE_X/Y`) and re-renders; at a map edge it crosses using
+that connection's `*Alignment` offset (vertical: Y=align, X+=align; horizontal:
+X=align, Y+=align) and `LoadMapData`s the neighbour, or clamps if there's none.
+No walk engine, no character movement. See `tools/render_overworld.py` for the
+ground-truth map that proved connections join maps along shared edges with an
+offset -- the same math this camera uses to cross seams.
 
 ## Build
 
diff --git a/engine/slop_menu.asm b/engine/slop_menu.asm
index b4b7f78e..66a8a482 100644
--- a/engine/slop_menu.asm
+++ b/engine/slop_menu.asm
@@ -216,30 +216,206 @@ WarpMapTable:
 
 
 ; ===========================================================================
-; EXPLORE (P1): overworld map-connection browser. Renders the current map (no
-; NPCs), and U/D/L/R jump to the connected map in that direction if one exists
-; (via wCurMapConnections + the connection headers). B restores the original
-; map and returns to the SL0P menu. No warping yet - read-only browse.
-; ===========================================================================
-; ===========================================================================
-; EXPLORE: toggle noclip free-roam. With noclip on, CollisionCheckOnLand is
-; bypassed, so you glide through walls / NPCs / ledges and cross map connection
-; seams exactly as the world data defines them. Closes the menu so you drop
-; straight back into the overworld to roam. Pick it again to turn it off.
+; EXPLORE: a screen-paging overworld camera. Each d-pad press INSTANTLY redraws
+; the next screenful of the world -- no character walking. At a map edge it hops
+; to the connected map using that connection's alignment offset (or clamps if
+; there's none). B restores the origin view and returns to the SL0P menu. It is
+; self-contained: it renders straight from the map block buffer (wOverworldMap)
+; and never touches the walk engine.
 ; ===========================================================================
+DEF SLOP_PAGE_X EQU 10          ; coords moved per horizontal page (~one screen)
+DEF SLOP_PAGE_Y EQU 8          ; coords moved per vertical page
+
 SlopExplore:
-	ld a, [wSlopNoclip]
-	xor $01
-	ld [wSlopNoclip], a
-; close the menu the same way the B button does (rebuild the overworld) instead
-; of .exitProceed, which only bare-returns and assumes a warp will redraw.
-	pop hl                         ; drop the pushed .afterHandler return address
-	call SlopMenuRestoreFlags
-	ld a, $01
-	ld [wUpdateSpritesEnabled], a
-	ldh a, [hLoadedROMBank]
+; save origin (map, coords, block coords, view pointer) to restore on exit
+	ld a, [wYCoord]
+	ld b, a
+	ld a, [wXCoord]
+	ld c, a
+	push bc
+	ld a, [wYBlockCoord]
+	ld b, a
+	ld a, [wXBlockCoord]
+	ld c, a
+	push bc
+	ld a, [wCurrentTileBlockMapViewPointer]
+	ld b, a
+	ld a, [wCurrentTileBlockMapViewPointer + 1]
+	ld c, a
+	push bc
+	ld a, [wCurMap]
 	push af
-	jp CloseTextDisplay
+	call LoadMapData               ; reload current map + tileset (menu clobbered VRAM)
+.renderView
+; block-aligned camera; view pointer = wOverworldMap + (by+1)*stride + bx,
+; where by = wYCoord/2, bx = wXCoord/2, stride = wCurMapWidth + 2*MAP_BORDER.
+	xor a
+	ld [wYBlockCoord], a
+	ld [wXBlockCoord], a
+	ld a, [wCurMapWidth]
+	add MAP_BORDER * 2
+	ld c, a
+	ld b, 0
+	ld a, [wYCoord]
+	srl a
+	inc a
+	ld hl, 0
+.mulRow
+	add hl, bc
+	dec a
+	jr nz, .mulRow
+	ld a, [wXCoord]
+	srl a
+	add l
+	ld l, a
+	jr nc, .noCarry
+	inc h
+.noCarry
+	ld bc, wOverworldMap
+	add hl, bc
+	ld a, l
+	ld [wCurrentTileBlockMapViewPointer], a
+	ld a, h
+	ld [wCurrentTileBlockMapViewPointer + 1], a
+	call LoadCurrentMapView
+	ld b, HIGH(vBGMap0)
+	call CopyScreenTileBufferToVRAM
+	ldh a, [rLCDC]                 ; hide sprites for a clean camera
+	res B_LCDC_OBJS, a
+	ldh [rLCDC], a
+	ld a, $90
+	ldh [hWY], a
+.input
+	call DelayFrame
+	call JoypadLowSensitivity
+	ldh a, [hJoyPressed]
+	ld d, a
+	bit B_PAD_B, d
+	jp nz, .exit
+	bit B_PAD_UP, d
+	jr z, .ckDown
+	ld a, [wYCoord]
+	sub SLOP_PAGE_Y
+	jp nc, .setY
+	ld hl, wNorthConnectedMap
+	ld de, wNorthConnectedMapYAlignment
+	ld a, 0                        ; clamp target = top
+	jp .crossV
+.ckDown
+	bit B_PAD_DOWN, d
+	jr z, .ckLeft
+	ld a, [wCurrentMapHeight2]
+	dec a
+	ld b, a                        ; b = max Y
+	ld a, [wYCoord]
+	add SLOP_PAGE_Y
+	cp b
+	jp c, .setY
+	jp z, .setY
+	ld hl, wSouthConnectedMap
+	ld de, wSouthConnectedMapYAlignment
+	ld a, b                        ; clamp target = max Y
+	jp .crossV
+.ckLeft
+	bit B_PAD_LEFT, d
+	jr z, .ckRight
+	ld a, [wXCoord]
+	sub SLOP_PAGE_X
+	jp nc, .setX
+	ld hl, wWestConnectedMap
+	ld de, wWestConnectedMapYAlignment
+	ld a, 0
+	jp .crossH
+.ckRight
+	bit B_PAD_RIGHT, d
+	jp z, .input
+	ld a, [wCurrentMapWidth2]
+	dec a
+	ld b, a                        ; b = max X
+	ld a, [wXCoord]
+	add SLOP_PAGE_X
+	cp b
+	jp c, .setX
+	jp z, .setX
+	ld hl, wEastConnectedMap
+	ld de, wEastConnectedMapYAlignment
+	ld a, b
+	jp .crossH
+.setY
+	ld [wYCoord], a
+	jp .renderView
+.setX
+	ld [wXCoord], a
+	jp .renderView
+; vertical cross (up/down): hl -> connected-map byte, de -> its YAlignment,
+; a = Y to clamp to when there is no connection.
+.crossV
+	ld b, a
+	ld a, [hl]
+	inc a
+	jr z, .clampY                  ; $ff -> no connection
+	ld a, [de]                     ; YAlignment -> new Y (absolute)
+	ld c, a
+	inc de
+	ld a, [de]                     ; XAlignment -> added to X
+	ld b, a
+	ld a, [wXCoord]
+	add b
+	ld [wXCoord], a
+	ld a, c
+	ld [wYCoord], a
+	ld a, [hl]
+	ld [wCurMap], a
+	call LoadMapData
+	jp .renderView
+.clampY
+	ld a, b
+	ld [wYCoord], a
+	jp .renderView
+; horizontal cross (left/right): hl -> connected-map byte, de -> its YAlignment,
+; a = X to clamp to when there is no connection.
+.crossH
+	ld b, a
+	ld a, [hl]
+	inc a
+	jr z, .clampX
+	ld a, [de]                     ; YAlignment -> added to Y
+	ld c, a
+	inc de
+	ld a, [de]                     ; XAlignment -> new X (absolute)
+	ld [wXCoord], a
+	ld a, [wYCoord]
+	add c
+	ld [wYCoord], a
+	ld a, [hl]
+	ld [wCurMap], a
+	call LoadMapData
+	jp .renderView
+.clampX
+	ld a, b
+	ld [wXCoord], a
+	jp .renderView
+.exit
+	pop af
+	ld [wCurMap], a
+	pop bc
+	ld a, b
+	ld [wCurrentTileBlockMapViewPointer], a
+	ld a, c
+	ld [wCurrentTileBlockMapViewPointer + 1], a
+	pop bc
+	ld a, b
+	ld [wYBlockCoord], a
+	ld a, c
+	ld [wXBlockCoord], a
+	pop bc
+	ld a, b
+	ld [wYCoord], a
+	ld a, c
+	ld [wXCoord], a
+	call LoadMapData               ; restore origin view (renders from restored pointer)
+	and a                          ; carry clear -> back to SL0P menu
+	ret
 
 ; ===========================================================================
 ; ITEMS submenu: give 99 of the chosen item (stacks via GiveItem)
diff --git a/home/overworld.asm b/home/overworld.asm
index 95b94646..bac16375 100644
--- a/home/overworld.asm
+++ b/home/overworld.asm
@@ -1218,9 +1218,6 @@ SignLoop::
 ; function to check if the player will jump down a ledge and check if the tile ahead is passable (when not surfing)
 ; sets the carry flag if there is a collision, and unsets it if there isn't a collision
 CollisionCheckOnLand::
-	ld a, [wSlopNoclip] ; SL0P noclip: walk through everything (carry clear)
-	and a
-	ret nz
 	ld a, [wMovementFlags]
 	bit BIT_LEDGE_OR_FISHING, a
 	jr nz, .noCollision
@@ -1232,7 +1229,6 @@ CollisionCheckOnLand::
 	ld d, a
 	ld a, [wSpritePlayerStateData1CollisionData]
 	and d ; check if a sprite is in the direction the player is trying to go
-	nop ; ??? why is this in the code
 	jr nz, .collision
 	xor a
 	ldh [hTextID], a
diff --git a/home/yes_no.asm b/home/yes_no.asm
index 8d995832..befcd3c4 100644
--- a/home/yes_no.asm
+++ b/home/yes_no.asm
@@ -5,11 +5,7 @@ YesNoChoice::
 	call InitYesNoTextBoxParameters
 	jr DisplayYesNoChoice
 
-TwoOptionMenu:: ; unreferenced
-	ld a, TWO_OPTION_MENU
-	ld [wTextBoxID], a
-	call InitYesNoTextBoxParameters
-	jp DisplayTextBoxID
+; SL0P: removed unreferenced TwoOptionMenu to reclaim ROM0 for the noclip guard.
 
 InitYesNoTextBoxParameters::
 	xor a ; YES_NO_MENU
@@ -26,12 +22,7 @@ YesNoChoicePokeCenter::
 	lb bc, 8, 12
 	jr DisplayYesNoChoice
 
-WideYesNoChoice:: ; unreferenced
-	call SaveScreenTilesToBuffer1
-	ld a, WIDE_YES_NO_MENU
-	ld [wTwoOptionMenuID], a
-	hlcoord 12, 7
-	lb bc, 8, 13
+; SL0P: removed unreferenced WideYesNoChoice to reclaim ROM0.
 
 DisplayYesNoChoice::
 	ld a, TWO_OPTION_MENU