explore: press A to warp to the viewed location

In the paging camera, A now drops the player onto the map you're looking at. It
scans outward from the screen centre (wTileMap col 8,row 9 = the view centre) for
the nearest tile that IsTilePassable, adjusts wYCoord/wXCoord to it, sets
wDestinationWarpID=$ff so LoadMapData enters at those coords, and returns carry
set to close the menu and resume the overworld right there. Factored the view-
pointer math into SlopSetViewPtr (shared by the camera + the warp landing).

Verified: browse Pallet -> Route 1, A -> player lands on Route 1 at the centre
tile and walks around normally (sprite + Pikachu, wild data intact).

1 files changed, 110 insertions, 28 deletions

diff --git a/engine/slop_menu.asm b/engine/slop_menu.asm
index 258770f5..2e1adaaa 100644
--- a/engine/slop_menu.asm
+++ b/engine/slop_menu.asm
@@ -247,36 +247,10 @@ SlopExplore:
 	push af
 	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 [wYBlockCoord], a           ; block-aligned camera centred on wYCoord/wXCoord
 	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 SlopSetViewPtr
 	call LoadCurrentMapView
 	ld b, HIGH(vBGMap0)
 	call CopyScreenTileBufferToVRAM
@@ -369,6 +343,8 @@ SlopExplore:
 	ld d, a
 	bit B_PAD_B, d
 	jp nz, .exit
+	bit B_PAD_A, d
+	jp nz, .warp
 	bit B_PAD_UP, d
 	jr z, .ckDown
 	ld a, [wYCoord]
@@ -472,6 +448,73 @@ SlopExplore:
 	ld a, b
 	ld [wXCoord], a
 	jp .renderView
+; ---- A: warp the player to the walkable tile nearest the screen centre ----
+; the centre tile is wTileMap(col 8,row 9) = coord (wYCoord,wXCoord); a coord
+; offset (dy,dx) maps to wTileMap(8+2dx, 9+2dy). Scan outward for a passable tile.
+.warp
+	ld hl, SlopWarpOffsets
+.warpScan
+	ld a, [hli]
+	cp $80
+	jr z, .warpGo                  ; nothing walkable found -> land on the centre
+	ld d, a                        ; d = dy
+	ld a, [hli]
+	ld e, a                        ; e = dx
+	push hl
+	ld a, d
+	add a
+	add 9                          ; row = 9 + 2*dy
+	ld b, a
+	ld hl, wTileMap
+.warpRow
+	ld a, b
+	and a
+	jr z, .warpCol
+	ld a, 20
+	add l
+	ld l, a
+	jr nc, .warpRowNC
+	inc h
+.warpRowNC
+	dec b
+	jr .warpRow
+.warpCol
+	ld a, e
+	add a
+	add 8                          ; col = 8 + 2*dx
+	add l
+	ld l, a
+	jr nc, .warpColNC
+	inc h
+.warpColNC
+	ld a, [hl]
+	ld c, a
+	call IsTilePassable            ; carry clear -> walkable
+	pop hl
+	jr c, .warpScan
+	ld a, [wYCoord]
+	add d
+	ld [wYCoord], a
+	ld a, [wXCoord]
+	add e
+	ld [wXCoord], a
+.warpGo
+	ld a, $ff
+	ld [wDestinationWarpID], a     ; enter at wYCoord/wXCoord (not a warp position)
+	ld a, [wYCoord]
+	and 1
+	ld [wYBlockCoord], a
+	ld a, [wXCoord]
+	and 1
+	ld [wXBlockCoord], a
+	call SlopSetViewPtr
+	call LoadMapData               ; enter the map (player sprite, wild data, warps)
+	pop af                         ; drop the 4 saved-origin values (we're staying here)
+	pop bc
+	pop bc
+	pop bc
+	scf                            ; carry set -> close menu, resume overworld here
+	ret
 .exit
 	pop af
 	ld [wCurMap], a
@@ -494,6 +537,45 @@ SlopExplore:
 	and a                          ; carry clear -> back to SL0P menu
 	ret
 
+; wCurrentTileBlockMapViewPointer = wOverworldMap + (wYCoord/2 + 1)*stride + wXCoord/2
+SlopSetViewPtr:
+	ld a, [wCurMapWidth]
+	add MAP_BORDER * 2
+	ld c, a
+	ld b, 0
+	ld a, [wYCoord]
+	srl a
+	inc a
+	ld hl, 0
+.loop
+	add hl, bc
+	dec a
+	jr nz, .loop
+	ld a, [wXCoord]
+	srl a
+	add l
+	ld l, a
+	jr nc, .nc
+	inc h
+.nc
+	ld bc, wOverworldMap
+	add hl, bc
+	ld a, l
+	ld [wCurrentTileBlockMapViewPointer], a
+	ld a, h
+	ld [wCurrentTileBlockMapViewPointer + 1], a
+	ret
+
+; (dy, dx) coord offsets scanned outward from the centre for a walkable tile
+SlopWarpOffsets:
+	db  0, 0
+	db -1, 0,  1, 0,  0,-1,  0, 1
+	db -1,-1, -1, 1,  1,-1,  1, 1
+	db -2, 0,  2, 0,  0,-2,  0, 2
+	db -2,-1, -2, 1,  2,-1,  2, 1, -1,-2, -1, 2,  1,-2,  1, 2
+	db -3, 0,  3, 0,  0,-3,  0, 3
+	db $80
+
 ; ===========================================================================
 ; ITEMS submenu: give 99 of the chosen item (stacks via GiveItem)
 ; ===========================================================================