1 files changed, 273 insertions, 0 deletions
diff --git a/engine/events/treemons.asm b/engine/events/treemons.asm
new file mode 100644
index 00000000..94782643
--- /dev/null
+++ b/engine/events/treemons.asm
@@ -0,0 +1,273 @@
+TreeMonEncounter:
+	xor a
+	ld [wTempWildMonSpecies], a
+	ld [wCurPartyLevel], a
+
+	ld hl, TreeMonMaps
+	call GetTreeMonSet
+	jr nc, .no_battle
+
+	call GetTreeMons
+	jr nc, .no_battle
+
+	call GetTreeMon
+	jr nc, .no_battle
+
+	ld a, BATTLETYPE_TREE
+	ld [wBattleType], a
+	ld a, 1
+	ld [wScriptVar], a
+	ret
+
+.no_battle
+	xor a
+	ld [wScriptVar], a
+	ret
+
+RockMonEncounter:
+	xor a
+	ld [wTempWildMonSpecies], a
+	ld [wCurPartyLevel], a
+
+	ld hl, RockMonMaps
+	call GetTreeMonSet
+	jr nc, .no_battle
+
+	call GetTreeMons
+	jr nc, .no_battle
+
+	; 40% chance of an encounter
+	ld a, 10
+	call RandomRange
+	cp 4
+	jr nc, .no_battle
+
+	call SelectTreeMon
+	jr nc, .no_battle
+
+	ret
+
+.no_battle
+	xor a
+	ret
+
+db $05 ; ????
+
+GetTreeMonSet:
+; Return carry and treemon set in a
+; if the current map is in table hl.
+	ld a, [wMapNumber]
+	ld e, a
+	ld a, [wMapGroup]
+	ld d, a
+.loop
+	ld a, [hli]
+	cp -1
+	jr z, .not_in_table
+
+	cp d
+	jr nz, .skip2
+
+	ld a, [hli]
+	cp e
+	jr nz, .skip1
+
+	jr .in_table
+
+.skip2
+	inc hl
+.skip1
+	inc hl
+	jr .loop
+
+.not_in_table
+	xor a
+	ret
+
+.in_table
+	ld a, [hl]
+	scf
+	ret
+
+INCLUDE "data/wild/treemon_maps.asm"
+
+GetTreeMons:
+; Return the address of TreeMon table a in hl.
+; Return nc if table a doesn't exist.
+
+	cp NUM_TREEMON_SETS
+	jr nc, .quit
+
+	and a
+	jr z, .quit
+
+	ld e, a
+	ld d, 0
+	ld hl, TreeMons
+	add hl, de
+	add hl, de
+
+	ld a, [hli]
+	ld h, [hl]
+	ld l, a
+
+	scf
+	ret
+
+.quit
+	xor a
+	ret
+
+INCLUDE "data/wild/treemons.asm"
+
+GetTreeMon:
+	push hl
+	call GetTreeScore
+	pop hl
+	and a ; TREEMON_SCORE_BAD
+	jr z, .bad
+	cp TREEMON_SCORE_GOOD
+	jr z, .good
+	cp TREEMON_SCORE_RARE
+	jr z, .rare
+	ret
+
+.bad
+	; 10% chance of an encounter
+	ld a, 10
+	call RandomRange
+	and a
+	jr nz, NoTreeMon
+	jr SelectTreeMon
+
+.good
+	; 50% chance of an encounter
+	ld a, 10
+	call RandomRange
+	cp 5
+	jr nc, NoTreeMon
+	jr SelectTreeMon
+
+.rare
+	; 80% chance of an encounter
+	ld a, 10
+	call RandomRange
+	cp 8
+	jr nc, NoTreeMon
+	jr .skip
+.skip
+	ld a, [hli]
+	cp -1
+	jr nz, .skip
+	call SelectTreeMon
+	ret
+
+SelectTreeMon:
+; Read a TreeMons table and pick one monster at random.
+
+	ld a, 100
+	call RandomRange
+.loop
+	sub [hl]
+	jr c, .ok
+	inc hl
+	inc hl
+	inc hl
+	jr .loop
+
+.ok
+	ld a, [hli]
+	cp -1
+	jr z, NoTreeMon
+
+	ld a, [hli]
+	ld [wTempWildMonSpecies], a
+	ld a, [hl]
+	ld [wCurPartyLevel], a
+	scf
+	ret
+
+NoTreeMon:
+	xor a
+	ld [wTempWildMonSpecies], a
+	ld [wCurPartyLevel], a
+	ret
+
+GetTreeScore:
+	call .CoordScore
+	ld [wBuffer1], a
+	call .OTIDScore
+	ld [wBuffer2], a
+	ld c, a
+	ld a, [wBuffer1]
+	sub c
+	jr z, .rare
+	jr nc, .ok
+	add 10
+.ok
+	cp 5
+	jr c, .good
+
+.bad
+	xor a ; TREEMON_SCORE_BAD
+	ret
+
+.good
+	ld a, TREEMON_SCORE_GOOD
+	ret
+
+.rare
+	ld a, TREEMON_SCORE_RARE
+	ret
+
+.CoordScore:
+	call GetFacingTileCoord
+	ld hl, 0
+	ld c, e
+	ld b, 0
+	ld a, d
+
+	and a
+	jr z, .next
+.loop
+	add hl, bc
+	dec a
+	jr nz, .loop
+.next
+
+	add hl, bc
+	ld c, d
+	add hl, bc
+
+	ld a, h
+	ldh [hDividend], a
+	ld a, l
+	ldh [hDividend + 1], a
+	ld a, 5
+	ldh [hDivisor], a
+	ld b, 2
+	call Divide
+
+	ldh a, [hQuotient + 2]
+	ldh [hDividend], a
+	ldh a, [hQuotient + 3]
+	ldh [hDividend + 1], a
+	ld a, 10
+	ldh [hDivisor], a
+	ld b, 2
+	call Divide
+
+	ldh a, [hRemainder]
+	ret
+
+.OTIDScore:
+	ld a, [wPlayerID]
+	ldh [hDividend], a
+	ld a, [wPlayerID + 1]
+	ldh [hDividend + 1], a
+	ld a, 10
+	ldh [hDivisor], a
+	ld b, 2
+	call Divide
+	ldh a, [hRemainder]
+	ret