From 57b27449a4ab5bac7490c04f725dc001c6e0ab6c Mon Sep 17 00:00:00 2001
From: Louis Pearson <opensource@louispearson.work>
Date: Fri, 19 Apr 2024 14:03:13 -0600
Subject: [PATCH] feat: gravity kind of works

---
 main.asm | 189 +++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 121 insertions(+), 68 deletions(-)

diff --git a/main.asm b/main.asm
index 48c1805..b144b1e 100644
--- a/main.asm
+++ b/main.asm
@@ -43,23 +43,42 @@ WaitVBlank:
 
 	; Reset positions
 	ld hl, wMetaspritePosition.x
-	ld a, 0
+	ld a, $10
 	ld [wMetaspritePosition.x], a
-	ld a, $80
+	ld a, $0
 	ld [wMetaspritePosition.x + 1], a
 
 	ld hl, wMetaspritePosition.y
-	ld a, 0
+	ld a, $10
 	ld [wMetaspritePosition.y], a
-	ld a, $80
+	ld a, $01
 	ld [wMetaspritePosition.y + 1], a
 
 	ld hl, wMetaspritePosition.z
-	ld a, 0
+	ld a, $00
 	ld [wMetaspritePosition.z], a 
-	ld a, 0
+	ld a, $0
 	ld [wMetaspritePosition.z + 1], a 
 
+	; Reset velocity
+	ld hl, wMetaspriteVelocity.x
+	ld a, $0
+	ld [wMetaspriteVelocity.x], a
+	ld a, $0
+	ld [wMetaspriteVelocity.x + 1], a
+
+	ld hl, wMetaspriteVelocity.y
+	ld a, $0
+	ld [wMetaspriteVelocity.y], a
+	ld a, $0
+	ld [wMetaspriteVelocity.y + 1], a
+
+	ld hl, wMetaspriteVelocity.z
+	ld a, $0
+	ld [wMetaspriteVelocity.z], a 
+	ld a, $0
+	ld [wMetaspriteVelocity.z + 1], a 
+
 	; Copy the tile data
 	ld de, Tiles
 	ld hl, $9000
@@ -91,10 +110,19 @@ WaitVBlank:
 	; Enable interrupts 
 	ei
 
-Main:
+Main::
 	call ResetShadowOAM
 	call UpdateJoypadState
+	call HandleInput
+	call HandlePhysics
+	call HandleRender
 
+	halt
+	nop
+
+	jp Main
+ 
+HandleInput::
 	ld a, [wJoypadState]
 	bit PADB_LEFT, a
 	jr nz, .leftend
@@ -151,46 +179,22 @@ Main:
 	ld [wMetaspritePosition.y+1], a
 .downend: 
 
-	ld a, [wJoypadState]
+	ld a, [wJoypadPressed]
 	bit PADB_A, a
-	jr nz, .jumpend
+	jr z, .jumpend
 
-	ld a, [wMetaspritePosition.z]
-	add a, 16
+	ld a, [wMetaspriteVelocity.z]
+	sub a, $F0
 	ld b, a
-	ld [wMetaspritePosition.z], a
-	ld a, [wMetaspritePosition.z+1]
-	adc 0
+	ld [wMetaspriteVelocity.z], a
+	ld a, [wMetaspriteVelocity.z+1]
+	sbc a, $00
 	ld c, a
-	ld [wMetaspritePosition.z+1], a
-
+	ld [wMetaspriteVelocity.z+1], a 
 .jumpend:
+	ret
 
-	ld a, [wJoypadState]
-	bit PADB_B, a
-	jr nz, .fallend
-
-	ld a, [wMetaspritePosition.z + 1]
-	cp 0
-	jr nz, .fall
-	ld a, [wMetaspritePosition.z]
-	cp 16
-	jr nc, .fall
-	ld a, 0
-	ld [wMetaspritePosition.z], a
-	jr .fallend
-
-.fall:
-	ld a, [wMetaspritePosition.z]
-	sub a, 16
-	ld b, a
-	ld [wMetaspritePosition.z], a
-	ld a, [wMetaspritePosition.z+1]
-	sbc 0
-	ld c, a
-	ld [wMetaspritePosition.z+1], a  
-.fallend:
-
+HandleRender::
 	; Render the player
 	; load de
 	ld a, [wMetaspritePosition.x]
@@ -202,12 +206,12 @@ Main:
 	ld a, [wMetaspritePosition.z]
 	ld c, a
 	ld a, [wMetaspritePosition.y]
-	sub a, c
+	add a, c
 	ld c, a
 	ld a, [wMetaspritePosition.z + 1]
 	ld b, a
 	ld a, [wMetaspritePosition.y + 1]
-	sbc a, b
+	adc a, b
 	ld b, a
 
 	ld hl, CatMetasprite
@@ -228,31 +232,61 @@ Main:
 
 	ld hl, ShadowMetasprite
 	call RenderMetasprite
-
-
-	ldh a, [hFrameCounter]
-	inc a
-	ldh [hFrameCounter], a 
-
-	halt
-	nop
-
-	jp Main
-
-Memcopy::
-	dec bc
-	inc b
-	inc c
-.loop:
-	ld a, [de]
-	ld [hli], a
-	inc de
-	dec c
-	jr nz, .loop
-	dec b
-	jr nz, .loop
 	ret
 
+HandlePhysics::
+
+	; Skip gravity if on ground
+	ld a, [wMetaspritePosition.z]
+	ld b, a
+	ld a, [wMetaspritePosition.z + 1]
+	or a, b
+	cp 0
+	jr z, .endGravity
+
+	; Apply gravity
+	ld a, [wMetaspriteVelocity.z]
+	add a, $02
+	ld [wMetaspriteVelocity.z], a
+	ld a, [wMetaspriteVelocity.z+1]
+	adc a, $00
+	ld [wMetaspriteVelocity.z+1], a
+.endGravity:
+ 
+
+	; Calculate new z, place in bc
+	ld a, [wMetaspriteVelocity.z]
+	ld c, a
+	ld a, [wMetaspritePosition.z]
+	add c
+	ld a, [wMetaspriteVelocity.z + 1]
+	ld b, a
+	ld a, [wMetaspritePosition.z + 1]
+	adc b
+
+	; If z is greater than or equal to 0, pos/vel to 0
+	jr nz, .endLanding1
+	jr nc, .endLanding1
+.startLanding
+	ld a, 0
+	ld [wMetaspriteVelocity.z], a
+	ld [wMetaspriteVelocity.z+1], a
+	ld c, 0
+	ld b, 0
+	jr .endLanding
+.endLanding1
+	nop
+.endLanding
+
+	; Update z position
+	ld a, c
+	ld [wMetaspritePosition.z], a
+	ld a, b
+	ld [wMetaspritePosition.z+1], a
+
+	ret
+
+SECTION "Joypad Routine", ROM0
 UpdateJoypadState::
 	ld hl, rP1
 	ld [hl], P1F_GET_BTN
@@ -287,6 +321,20 @@ UpdateJoypadState::
 	ld [wJoypadState], a
 	ret
 
+SECTION "MemCopy Routine", ROM0
+Memcopy::
+	dec bc
+	inc b
+	inc c
+.loop:
+	ld a, [de]
+	ld [hli], a
+	inc de
+	dec c
+	jr nz, .loop
+	dec b
+	jr nz, .loop
+	ret  
 
 SECTION "VBlank Interrupt", ROM0[$0040]
 VBlankInterrupt:
@@ -443,7 +491,7 @@ ShadowMetasprite:
 
 SECTION "Position Vars", WRAM0 
 ; Q12.4 fixed-point X posiition
-wMetaspritePosition:
+wMetaspritePosition::
 .x:
 	dw
 .y:
@@ -453,7 +501,12 @@ wMetaspritePosition:
 
 ; Q4.4 fixed-point velocity
 wMetaspriteVelocity::
-	db
+.x:
+	dw
+.y:
+	dw
+.z:
+	dw
 
 SECTION "Joypad Vars", WRAM0
 wJoypadState: