SL0P menu: add SAVER screensaver (autopilot EXPLORE)

New menu entry that auto-drives the EXPLORE camera across the overworld:
- persistent-direction wander (DFS-ish): keep heading, turn only when blocked
  or occasionally at a junction, never an immediate U-turn. SlopSaverPickDir
  synthesises a d-pad direction into the normal EXPLORE dispatch, so it inherits
  smooth scrolling and smooth map-edge crossing.
- arrows hidden; player/Pikachu never drawn (clear+freeze OAM right after every
  LoadMapData, before the first frame renders - also fixes a brief player flash
  at crossings in manual EXPLORE).
- any button wakes it back to the menu.

State byte wSlopSaverDir reuses wUnusedCreditsByte (0=off, else current dir).

1 files changed, 191 insertions, 2 deletions

diff --git a/engine/slop_menu.asm b/engine/slop_menu.asm
index 36654111..09650150 100644
--- a/engine/slop_menu.asm
+++ b/engine/slop_menu.asm
@@ -8,7 +8,7 @@
 ; To add an entry: add a "NAME" line to SlopMenuText, a `dw Handler` to
 ; SlopMenuHandlers, and bump SLOP_MENU_COUNT.
 
-DEF SLOP_MENU_COUNT EQU 13
+DEF SLOP_MENU_COUNT EQU 14
 
 SECTION "Slop Menu", ROMX
 
@@ -121,7 +121,8 @@ SlopMenuText:
 	next "ITEMS"
 	next "NOWILD"
 	next "REPEL"
-	next "EXPLORE@"
+	next "EXPLORE"
+	next "SAVER@"
 SlopOnText:
 	db "ON@"
 SlopMenuHandlers:
@@ -138,6 +139,7 @@ SlopMenuHandlers:
 	dw SlopToggleNoWild
 	dw SlopRepel
 	dw SlopExplore
+	dw SlopSaver
 
 
 ; ===========================================================================
@@ -230,7 +232,23 @@ DEF SLOP_PAGE_Y EQU 8          ; coords moved per vertical page
 DEF SLOP_SCROLL_PX EQU 8
 DEF SLOP_SCROLL_FRAMES EQU 16 / SLOP_SCROLL_PX
 
+SlopSaver:
+; SCREENSAVER: auto-scroll the overworld. Seed an initial direction; the rest is
+; identical to EXPLORE (shared body), driven by SlopSaverPickDir in the loop.
+	ld a, PAD_DOWN
+	ld [wSlopSaverDir], a
+	jr SlopExploreShared
 SlopExplore:
+	xor a
+	ld [wSlopSaverDir], a
+SlopExploreShared:
+; wait for the opening button to be released so it isn't read as EXPLORE input
+.waitRelease
+	call DelayFrame
+	call Joypad                    ; VBlank only reads raw input; Joypad updates hJoyHeld
+	ldh a, [hJoyHeld]
+	and a
+	jr nz, .waitRelease
 ; save origin (map, coords, block coords, view pointer) to restore on exit
 	ld a, [wYCoord]
 	ld b, a
@@ -251,12 +269,21 @@ SlopExplore:
 	push af
 	call LoadMapData               ; reload current map + tileset (menu clobbered VRAM)
 .renderView
+; LoadMapData (entry/cross) re-enables sprites and reloads the player + Pikachu
+; follower. Freeze and clear OAM now, before the first frame renders, so they are
+; never drawn during EXPLORE/screensaver.
+	ld a, $ff
+	ld [wUpdateSpritesEnabled], a
+	call ClearSprites
 	call SlopExploreRenderBG        ; fresh render to vBGMap0, hardware scroll reset
 .renderArrows
 	call LoadFontTilePatterns      ; arrow glyphs ($ed/$ee) into VRAM for the OBJ layer
 ; draw a direction-arrow sprite for each direction the camera can currently move:
 ; either there's more map that way, or the map has a connection that way.
 	call ClearSprites
+	ld a, [wSlopSaverDir]
+	and a
+	jp nz, .arrowsDone             ; screensaver hides the direction arrows
 	ld hl, wShadowOAM
 ; up: movable unless at the top edge (wYCoord == 0) with no north connection
 	ld a, [wYCoord]
@@ -337,9 +364,20 @@ SlopExplore:
 	ldh [hWY], a
 .input
 	call DelayFrame
+	ld a, [wSlopSaverDir]
+	and a
+	jr nz, .saverInput
 	call JoypadLowSensitivity
 	ldh a, [hJoyPressed]
 	ld d, a
+	jr .dispatch
+.saverInput
+	call Joypad                    ; refresh hJoyHeld (VBlank only reads raw input)
+	ldh a, [hJoyHeld]              ; any real button wakes/exits the screensaver
+	and a
+	jp nz, .exit
+	call SlopSaverPickDir          ; d = auto-picked scroll direction
+.dispatch
 	bit B_PAD_B, d
 	jp nz, .exit
 	bit B_PAD_A, d
@@ -825,6 +863,157 @@ SlopScrollUp:
 	jr nz, .loop
 	ret
 
+; ===========================================================================
+; SCREENSAVER direction logic: a persistent-direction wander. Keep drifting one
+; way; only turn when the current direction gets blocked, or occasionally at a
+; junction. Avoids immediate U-turns so it glides smoothly (DFS-ish) across the
+; overworld instead of jittering. The chosen direction is fed into the normal
+; EXPLORE dispatch as if the d-pad were pressed, so it inherits smooth scrolling
+; and smooth map-edge crossing for free.
+; ===========================================================================
+SlopDirBits:
+	db PAD_UP, PAD_DOWN, PAD_LEFT, PAD_RIGHT
+
+; -> a = bitmask of currently-movable directions (same rule as the arrows)
+SlopValidDirMask:
+	ld c, 0
+	ld a, [wYCoord]
+	and a
+	jr nz, .up
+	ld a, [wNorthConnectedMap]
+	inc a
+	jr z, .noUp
+.up
+	set B_PAD_UP, c
+.noUp
+	ld a, [wCurrentMapHeight2]
+	dec a
+	ld b, a
+	ld a, [wYCoord]
+	cp b
+	jr nz, .down
+	ld a, [wSouthConnectedMap]
+	inc a
+	jr z, .noDown
+.down
+	set B_PAD_DOWN, c
+.noDown
+	ld a, [wXCoord]
+	and a
+	jr nz, .left
+	ld a, [wWestConnectedMap]
+	inc a
+	jr z, .noLeft
+.left
+	set B_PAD_LEFT, c
+.noLeft
+	ld a, [wCurrentMapWidth2]
+	dec a
+	ld b, a
+	ld a, [wXCoord]
+	cp b
+	jr nz, .right
+	ld a, [wEastConnectedMap]
+	inc a
+	jr z, .noRight
+.right
+	set B_PAD_RIGHT, c
+.noRight
+	ld a, c
+	ret
+
+; a = nonzero mask -> a = one set bit of it, chosen pseudo-randomly
+SlopRandomBit:
+	ld b, a                        ; b = mask
+	ldh a, [hRandomSub]
+	and $03
+	ld c, a                        ; random start index 0..3
+	ld d, 4
+.loop
+	ld a, c
+	and $03
+	ld hl, SlopDirBits
+	add l
+	ld l, a
+	ld a, 0
+	adc h
+	ld h, a
+	ld a, [hl]
+	and b
+	ret nz                         ; this direction is in the mask -> use it
+	inc c
+	dec d
+	jr nz, .loop
+	ld a, b                        ; fallback (a nonzero mask always hits above)
+	ret
+
+; a = dir bit -> a = the opposite direction bit
+SlopRevDir:
+	cp PAD_UP
+	jr nz, .notUp
+	ld a, PAD_DOWN
+	ret
+.notUp
+	cp PAD_DOWN
+	jr nz, .notDown
+	ld a, PAD_UP
+	ret
+.notDown
+	cp PAD_LEFT
+	jr nz, .notLeft
+	ld a, PAD_RIGHT
+	ret
+.notLeft
+	ld a, PAD_LEFT                  ; was RIGHT
+	ret
+
+; a = dir bit -> a = mask of the two perpendicular directions
+SlopPerpMask:
+	and PAD_UP | PAD_DOWN
+	ld a, PAD_LEFT | PAD_RIGHT      ; vertical dir -> horizontal perpendicular
+	ret nz
+	ld a, PAD_UP | PAD_DOWN
+	ret
+
+; pick the next screensaver direction; store in wSlopSaverDir, return it in d
+SlopSaverPickDir:
+	call SlopValidDirMask
+	ld e, a                        ; e = valid-direction mask
+	and a
+	jr z, .keepCurrent             ; nothing valid (shouldn't happen)
+	ld a, [wSlopSaverDir]
+	ld b, a                        ; b = current direction
+	and e
+	jr z, .blocked                 ; current direction no longer valid -> turn
+; current direction still valid: mostly keep going, occasionally turn
+	ldh a, [hRandomAdd]
+	and $07
+	jr nz, .keepCurrent            ; 7/8: carry straight on
+	ld a, b
+	call SlopPerpMask
+	and e                          ; valid perpendicular directions
+	jr z, .keepCurrent             ; none -> keep going
+	call SlopRandomBit
+	jr .store
+.blocked
+	ld a, b
+	call SlopRevDir
+	cpl
+	and e                          ; valid directions excluding a U-turn
+	jr z, .onlyReverse
+	call SlopRandomBit
+	jr .store
+.onlyReverse
+	ld a, e                        ; only a U-turn is available
+	call SlopRandomBit
+	jr .store
+.keepCurrent
+	ld a, [wSlopSaverDir]
+.store
+	ld [wSlopSaverDir], a
+	ld d, a
+	ret
+
 ; (dy, dx) coord offsets scanned outward from the centre for a walkable tile
 SlopWarpOffsets:
 	db  0, 0