From 92856fd4b4908939ff4998a84369d4b9ac097b7a Mon Sep 17 00:00:00 2001
From: Ash Ketchum <no-reply@sl0p.foo>
Date: Wed, 15 Jul 2026 15:46:49 +0200
Subject: EXPLORE/SAVER: clamp camera into map bounds after a connection cross

Crossing a map connection applies the connection's alignment offset blindly.
At an edge position the connection doesn't span, the resulting coord lands
outside the neighbour (e.g. Y = -8 = $f8), and since the bounds checks then
operate on the wrapped value the camera roams far outside the map, rendering
whatever WRAM lies past wOverworldMap as on-screen garbage. SlopClampCoords
(run in .renderView, i.e. after every entry/cross LoadMapData) clamps wYCoord
to [0,maxY] and wXCoord to [0,maxX] of the freshly-loaded map.

Verified: 120-sample saver soak across 19 maps -> 0 out-of-bounds; manual
EXPLORE crossing unaffected.
---
 engine/slop_menu.asm | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/engine/slop_menu.asm b/engine/slop_menu.asm
index 7e534015..4c93e2ed 100644
--- a/engine/slop_menu.asm
+++ b/engine/slop_menu.asm
@@ -275,6 +275,7 @@ SlopExploreShared:
 	ld a, $ff
 	ld [wUpdateSpritesEnabled], a
 	call ClearSprites
+	call SlopClampCoords            ; a cross can land outside the new map -> clamp
 	call SlopExploreRenderBG        ; fresh render to vBGMap0, hardware scroll reset
 .renderArrows
 	call LoadFontTilePatterns      ; arrow glyphs ($ed/$ee) into VRAM for the OBJ layer
@@ -616,6 +617,38 @@ SlopExploreShared:
 	and a                          ; carry clear -> back to SL0P menu
 	ret
 
+; Clamp wYCoord to [0,maxY] and wXCoord to [0,maxX] of the current map. Crossing a
+; connection applies its alignment offset blindly, so at an edge position the
+; connection doesn't span the camera can land outside the neighbour; rendering
+; that reads past wOverworldMap into other WRAM = on-screen garbage.
+SlopClampCoords:
+	ld a, [wCurrentMapHeight2]
+	dec a
+	ld b, a                        ; maxY
+	ld a, [wYCoord]
+	call .clamp
+	ld [wYCoord], a
+	ld a, [wCurrentMapWidth2]
+	dec a
+	ld b, a                        ; maxX
+	ld a, [wXCoord]
+	call .clamp
+	ld [wXCoord], a
+	ret
+; a = coord, b = max -> a clamped to [0,max]. Out-of-range values >= $80 are
+; treated as "past the near edge" (negative) and clamped to 0, otherwise to max.
+.clamp
+	cp b
+	ret c
+	ret z
+	bit 7, a
+	jr nz, .zero
+	ld a, b
+	ret
+.zero
+	xor a
+	ret
+
 ; wCurrentTileBlockMapViewPointer = wOverworldMap + (wYCoord/2 + 1)*stride + wXCoord/2
 SlopSetViewPtr:
 	ld a, [wCurMapWidth]
-- 
cgit v1.3.1-sl0p