intro: real 2bpp graphic splash (POKeMON SL0P EDITION)

Replace the plain-text splash with an actual rendered graphic: gfx/slop/intro.png
(bordered banner, big drop-shadowed SL0P logo) -> deduped tiles + tilemap via a
custom rgbgfx Makefile rule (164 tiles). SlopSplash loads it into VRAM (BG map,
0x8000 tiles), holds ~2s, fades out, and restores LCDC_DEFAULT so the overworld
BG addressing + OBJ sprites are intact. Reproducible from the PNG.

4 files changed, 48 insertions, 16 deletions

diff --git a/.gitignore b/.gitignore
index 8952a16f..decf741d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,3 +32,4 @@
 *.sn*
 *.sa*
 *.sg1
+gfx/slop/intro.tilemap
diff --git a/Makefile b/Makefile
index d05541b0..085b78f3 100644
--- a/Makefile
+++ b/Makefile
@@ -171,6 +171,14 @@ gfx/sgb/border.2bpp: tools/gfx += --trim-whitespace
 gfx/surfing_pikachu/surfing_pikachu_1c.2bpp: tools/gfx += --trim-whitespace
 
 
+### Custom graphics rules
+
+# SL0P intro splash: dedup tiles (-u) and emit a tilemap (-t) alongside the
+# 2bpp, both INCBIN'd by engine/slop_intro.asm.
+gfx/slop/intro.2bpp: gfx/slop/intro.png
+	$(RGBGFX) $(RGBGFXFLAGS) -u -t gfx/slop/intro.tilemap -o $@ $<
+gfx/slop/intro.tilemap: gfx/slop/intro.2bpp ;
+
 ### Catch-all graphics rules
 
 %.2bpp: %.png
diff --git a/engine/slop_intro.asm b/engine/slop_intro.asm
index 84bbc53f..b3bcaaa6 100644
--- a/engine/slop_intro.asm
+++ b/engine/slop_intro.asm
@@ -1,27 +1,50 @@
-; Brief custom boot splash shown on the fastboot path (before the save is
-; loaded). Reuses the same display setup as the menu/text system.
+; Brief custom boot splash shown on the fastboot path. Loads a real 2bpp
+; graphic (gfx/slop/intro.png -> tiles+tilemap via rgbgfx) into VRAM and holds
+; it, then MainMenu's autoload continues into the game.
+
+DEF SLOP_INTRO_NUM_TILES EQU 164
 
 SECTION "Slop Intro", ROMX
 
 SlopSplash::
 	call ClearScreen
-	call LoadFontTilePatterns
-	call RunDefaultPaletteCommand
-	hlcoord 6, 7
-	ld de, .line1
-	call PlaceString
-	hlcoord 4, 9
-	ld de, .line2
-	call PlaceString
-	ld b, HIGH(vBGMap1)
+; load the custom tiles into the 0x8000 block (unsigned addressing)
+	ld hl, vChars0
+	ld de, SlopIntroTiles
+	ld b, BANK(SlopIntroTiles)
+	ld c, SLOP_INTRO_NUM_TILES
+	call CopyVideoData
+	ldh a, [rLCDC]
+	or LCDC_BLOCK01                    ; BG/window tile data at 0x8000
+	ldh [rLCDC], a
+; blit the 20x18 tilemap through wTileMap so the 20->32 row stride is handled.
+; Use the BG map (vBGMap0): the map load on continue overwrites it, so nothing
+; is left corrupting the overworld (unlike the window map vBGMap1).
+	ld hl, SlopIntroTilemap
+	ld de, wTileMap
+	ld bc, SlopIntroTilemapEnd - SlopIntroTilemap
+	call CopyData
+	ld b, HIGH(vBGMap0)
 	call CopyScreenTileBufferToVRAM
 	xor a
-	ldh [hWY], a
-	ld a, $01
-	ldh [hAutoBGTransferEnabled], a
+	ldh [hSCX], a
+	ldh [hSCY], a
+	ld a, LCDC_ON | LCDC_BLOCK01 | LCDC_BG_9800 | LCDC_BG_ON ; BG only, tiles @0x8000
+	ldh [rLCDC], a
+	call GBPalNormal
 	ld c, 120                          ; ~2 seconds
 	call DelayFrames
+	call GBFadeOutToWhite
+; restore the default LCDC so the overworld renders correctly: signed tile data
+; (BLOCK21) for the BG *and* OBJ back on so entity sprites reappear
+	ld a, LCDC_DEFAULT
+	ldh [rLCDC], a
 	ret
 
-.line1: db "POKéMON@"
-.line2: db "SL0P EDITION@"
+SlopIntroTiles:
+	INCBIN "gfx/slop/intro.2bpp"
+SlopIntroTilesEnd:
+
+SlopIntroTilemap:
+	INCBIN "gfx/slop/intro.tilemap"
+SlopIntroTilemapEnd:
diff --git a/gfx/slop/intro.png b/gfx/slop/intro.png
new file mode 100644
index 00000000..05358e52
--- /dev/null
+++ b/gfx/slop/intro.png