EXPLORE: smooth hardware-scroll animation for in-map page moves

1 files changed, 248 insertions, 19 deletions

diff --git a/engine/slop_menu.asm b/engine/slop_menu.asm
index 2e1adaaa..acad203c 100644
--- a/engine/slop_menu.asm
+++ b/engine/slop_menu.asm
@@ -225,6 +225,10 @@ WarpMapTable:
 ; ===========================================================================
 DEF SLOP_PAGE_X EQU 10          ; coords moved per horizontal page (~one screen)
 DEF SLOP_PAGE_Y EQU 8          ; coords moved per vertical page
+; smooth-scroll animation speed. SLOP_SCROLL_PX must divide 16 (one coord-step
+; is 16 px). Bigger = faster/steppier, smaller = slower/smoother.
+DEF SLOP_SCROLL_PX EQU 8
+DEF SLOP_SCROLL_FRAMES EQU 16 / SLOP_SCROLL_PX
 
 SlopExplore:
 ; save origin (map, coords, block coords, view pointer) to restore on exit
@@ -247,13 +251,8 @@ SlopExplore:
 	push af
 	call LoadMapData               ; reload current map + tileset (menu clobbered VRAM)
 .renderView
-	xor a
-	ld [wYBlockCoord], a           ; block-aligned camera centred on wYCoord/wXCoord
-	ld [wXBlockCoord], a
-	call SlopSetViewPtr
-	call LoadCurrentMapView
-	ld b, HIGH(vBGMap0)
-	call CopyScreenTileBufferToVRAM
+	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.
@@ -349,7 +348,7 @@ SlopExplore:
 	jr z, .ckDown
 	ld a, [wYCoord]
 	sub SLOP_PAGE_Y
-	jp nc, .setY
+	jp nc, .moveUp
 	ld hl, wNorthConnectedMap
 	ld de, wNorthConnectedMapYAlignment
 	ld a, 0                        ; clamp target = top
@@ -363,8 +362,8 @@ SlopExplore:
 	ld a, [wYCoord]
 	add SLOP_PAGE_Y
 	cp b
-	jp c, .setY
-	jp z, .setY
+	jp c, .moveDown
+	jp z, .moveDown
 	ld hl, wSouthConnectedMap
 	ld de, wSouthConnectedMapYAlignment
 	ld a, b                        ; clamp target = max Y
@@ -374,7 +373,7 @@ SlopExplore:
 	jr z, .ckRight
 	ld a, [wXCoord]
 	sub SLOP_PAGE_X
-	jp nc, .setX
+	jp nc, .moveLeft
 	ld hl, wWestConnectedMap
 	ld de, wWestConnectedMapYAlignment
 	ld a, 0
@@ -388,18 +387,30 @@ SlopExplore:
 	ld a, [wXCoord]
 	add SLOP_PAGE_X
 	cp b
-	jp c, .setX
-	jp z, .setX
+	jp c, .moveRight
+	jp z, .moveRight
 	ld hl, wEastConnectedMap
 	ld de, wEastConnectedMapYAlignment
 	ld a, b
 	jp .crossH
-.setY
-	ld [wYCoord], a
-	jp .renderView
-.setX
-	ld [wXCoord], a
-	jp .renderView
+; in-map page moves: smooth-scroll one screen, then just redraw the arrows
+; (the scroll already left the destination view on screen in rotated VRAM).
+.moveUp
+	ld c, SLOP_PAGE_Y
+	call SlopScrollUp
+	jp .renderArrows
+.moveDown
+	ld c, SLOP_PAGE_Y
+	call SlopScrollDown
+	jp .renderArrows
+.moveLeft
+	ld c, SLOP_PAGE_X
+	call SlopScrollLeft
+	jp .renderArrows
+.moveRight
+	ld c, SLOP_PAGE_X
+	call SlopScrollRight
+	jp .renderArrows
 ; vertical cross (up/down): hl -> connected-map byte, de -> its YAlignment,
 ; a = Y to clamp to when there is no connection.
 .crossV
@@ -566,6 +577,224 @@ SlopSetViewPtr:
 	ld [wCurrentTileBlockMapViewPointer + 1], a
 	ret
 
+; render the current view freshly to vBGMap0 and reset the hardware scroll so
+; the camera is block-aligned at SCX/SCY = 0. Used on entry, map-cross and
+; clamp (i.e. everywhere except the animated in-map page moves).
+SlopExploreRenderBG:
+	xor a
+	ld [wYBlockCoord], a           ; block-aligned camera centred on wYCoord/wXCoord
+	ld [wXBlockCoord], a
+	ldh [hAutoBGTransferEnabled], a ; use RedrawRowOrColumn path, not AutoBgMapTransfer
+	ld [wMapViewVRAMPointer], a
+	ldh [hSCX], a
+	ldh [hSCY], a
+	ld a, HIGH(vBGMap0)
+	ld [wMapViewVRAMPointer + 1], a
+	call SlopSetViewPtr
+	call LoadCurrentMapView
+	ld b, HIGH(vBGMap0)
+	jp CopyScreenTileBufferToVRAM
+
+; ---------------------------------------------------------------------------
+; Smooth EXPLORE scrolling. Each routine pans the camera `c` coords in one
+; direction, 16 px per coord-step, reusing the walking engine's rotating-VRAM
+; machinery: advance wMapViewVRAMPointer, re-render wTileMap for the new
+; position, inject the freshly exposed 2-tile edge with a Schedule*Redraw
+; (applied by RedrawRowOrColumn in VBlank), and ramp hSCX/hSCY SLOP_SCROLL_PX
+; px per frame. After an even coord count it ends block-aligned exactly where
+; SlopExploreRenderBG would have placed the view, so wTileMap / the block
+; pointer / arrow logic / warp scan are all consistent afterwards.
+; ---------------------------------------------------------------------------
+SlopScrollRight:
+	xor a
+	ldh [hAutoBGTransferEnabled], a
+.loop
+	push bc
+	ld a, [wXCoord]
+	inc a
+	ld [wXCoord], a
+	ld a, [wMapViewVRAMPointer]     ; VRAM col +2 (wrap within the 32-tile row)
+	ld e, a
+	and $e0
+	ld d, a
+	ld a, e
+	add 2
+	and $1f
+	or d
+	ld [wMapViewVRAMPointer], a
+	ld hl, wXBlockCoord
+	inc [hl]
+	ld a, [hl]
+	cp 2
+	jr nz, .go
+	ld [hl], 0                     ; crossed a block east -> advance block pointer
+	ld hl, wCurrentTileBlockMapViewPointer
+	inc [hl]
+	jr nz, .go
+	inc hl
+	inc [hl]
+.go
+	call LoadCurrentMapView
+	call ScheduleEastColumnRedraw
+	ld c, SLOP_SCROLL_FRAMES
+.frames
+	ldh a, [hSCX]
+	add SLOP_SCROLL_PX
+	ldh [hSCX], a
+	call DelayFrame
+	dec c
+	jr nz, .frames
+	pop bc
+	dec c
+	jr nz, .loop
+	ret
+
+SlopScrollLeft:
+	xor a
+	ldh [hAutoBGTransferEnabled], a
+.loop
+	push bc
+	ld a, [wXCoord]
+	dec a
+	ld [wXCoord], a
+	ld a, [wMapViewVRAMPointer]     ; VRAM col -2
+	ld e, a
+	and $e0
+	ld d, a
+	ld a, e
+	sub 2
+	and $1f
+	or d
+	ld [wMapViewVRAMPointer], a
+	ld hl, wXBlockCoord
+	dec [hl]
+	ld a, [hl]
+	inc a
+	jr nz, .go                     ; was 0 -> now $ff: crossed a block west
+	ld [hl], 1
+	ld hl, wCurrentTileBlockMapViewPointer
+	ld a, [hl]
+	sub 1
+	ld [hl], a
+	jr nc, .go
+	inc hl
+	dec [hl]
+.go
+	call LoadCurrentMapView
+	call ScheduleWestColumnRedraw
+	ld c, SLOP_SCROLL_FRAMES
+.frames
+	ldh a, [hSCX]
+	sub SLOP_SCROLL_PX
+	ldh [hSCX], a
+	call DelayFrame
+	dec c
+	jr nz, .frames
+	pop bc
+	dec c
+	jr nz, .loop
+	ret
+
+SlopScrollDown:
+	xor a
+	ldh [hAutoBGTransferEnabled], a
+.loop
+	push bc
+	ld a, [wYCoord]
+	inc a
+	ld [wYCoord], a
+	ld a, [wMapViewVRAMPointer]     ; VRAM row +1 (=+$40), wrap high byte into vBGMap0
+	add $40
+	ld [wMapViewVRAMPointer], a
+	jr nc, .vramDone
+	ld a, [wMapViewVRAMPointer + 1]
+	inc a
+	and $03
+	or $98
+	ld [wMapViewVRAMPointer + 1], a
+.vramDone
+	ld hl, wYBlockCoord
+	inc [hl]
+	ld a, [hl]
+	cp 2
+	jr nz, .go
+	ld [hl], 0                     ; crossed a block south -> advance block pointer
+	ld a, [wCurMapWidth]
+	add MAP_BORDER * 2
+	ld b, a
+	ld hl, wCurrentTileBlockMapViewPointer
+	ld a, [hl]
+	add b
+	ld [hl], a
+	jr nc, .go
+	inc hl
+	inc [hl]
+.go
+	call LoadCurrentMapView
+	call ScheduleSouthRowRedraw
+	ld c, SLOP_SCROLL_FRAMES
+.frames
+	ldh a, [hSCY]
+	add SLOP_SCROLL_PX
+	ldh [hSCY], a
+	call DelayFrame
+	dec c
+	jr nz, .frames
+	pop bc
+	dec c
+	jr nz, .loop
+	ret
+
+SlopScrollUp:
+	xor a
+	ldh [hAutoBGTransferEnabled], a
+.loop
+	push bc
+	ld a, [wYCoord]
+	dec a
+	ld [wYCoord], a
+	ld a, [wMapViewVRAMPointer]     ; VRAM row -1 (=-$40)
+	sub $40
+	ld [wMapViewVRAMPointer], a
+	jr nc, .vramDone
+	ld a, [wMapViewVRAMPointer + 1]
+	dec a
+	and $03
+	or $98
+	ld [wMapViewVRAMPointer + 1], a
+.vramDone
+	ld hl, wYBlockCoord
+	dec [hl]
+	ld a, [hl]
+	inc a
+	jr nz, .go                     ; was 0 -> now $ff: crossed a block north
+	ld [hl], 1
+	ld a, [wCurMapWidth]
+	add MAP_BORDER * 2
+	ld b, a
+	ld hl, wCurrentTileBlockMapViewPointer
+	ld a, [hl]
+	sub b
+	ld [hl], a
+	jr nc, .go
+	inc hl
+	dec [hl]
+.go
+	call LoadCurrentMapView
+	call ScheduleNorthRowRedraw
+	ld c, SLOP_SCROLL_FRAMES
+.frames
+	ldh a, [hSCY]
+	sub SLOP_SCROLL_PX
+	ldh [hSCY], a
+	call DelayFrame
+	dec c
+	jr nz, .frames
+	pop bc
+	dec c
+	jr nz, .loop
+	ret
+
 ; (dy, dx) coord offsets scanned outward from the centre for a walkable tile
 SlopWarpOffsets:
 	db  0, 0