From ee956b4ca73b061bd3a175af04c936be9d070cba Mon Sep 17 00:00:00 2001
From: Forest Belton <65484+forestbelton@users.noreply.github.com>
Date: Sat, 3 Jul 2021 17:50:11 -0400
Subject: [PATCH] Implement jump

---
 inc/util.inc    |  7 ++++
 src/collision.s |  2 ++
 src/player.s    | 96 +++++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 103 insertions(+), 2 deletions(-)
 create mode 100644 inc/util.inc

diff --git a/inc/util.inc b/inc/util.inc
new file mode 100644
index 0000000..21cdfc0
--- /dev/null
+++ b/inc/util.inc
@@ -0,0 +1,7 @@
+; Stores a 16-bit register into the address stored in HL
+; \1 The register to store
+MACRO STORE16
+    ld [hl], HIGH(\1)
+    inc hl
+    ld [hl], LOW(\1)
+ENDM
diff --git a/src/collision.s b/src/collision.s
index 83d3e2e..fb4f7fb 100644
--- a/src/collision.s
+++ b/src/collision.s
@@ -2,6 +2,8 @@ INCLUDE "oam.inc"
 
 SECTION "Collision", ROMX
 
+; Determines if player has hit the background
+; @return NZ = false, Z = true
 player_bg_collides::
     ; c = x % 8 == 0 ? x/8 : x/8 + 1
     ld hl, PLAYER_X
diff --git a/src/player.s b/src/player.s
index 1ec10db..d4540b1 100644
--- a/src/player.s
+++ b/src/player.s
@@ -1,6 +1,7 @@
 INCLUDE "hardware.inc"
 INCLUDE "input.inc"
 INCLUDE "oam.inc"
+INCLUDE "util.inc"
 
 Section "Player Data", WRAM0
 
@@ -12,6 +13,10 @@ PLAYER_X:: db
 PLAYER_Y:: db
 PLAYER_DIR:: db
 
+PLAYER_JUMPING:: db
+PLAYER_VY:: dw
+PLAYER_OLD_Y: db
+
 Section "Player Code", ROM0
 
 spriteData:
@@ -22,6 +27,9 @@ DEF SPRITE_IDX EQU 32 ; tile index, rename later
 DEF SPRITE_WIDTH EQU 2
 DEF SPRITE_HEIGHT EQU 2
 
+DEF GRAVITY EQU (0 << 8) | 8
+DEF INIT_VY EQU (2 << 8) | 40
+
 Player_Init::
     ; clear player data
     ld hl, PLAYER_X
@@ -30,6 +38,12 @@ Player_Init::
     ld [hl], 144-32
     inc hl
     ld [hl], 0
+    inc hl
+    ld [hl], 0
+    inc hl
+    ld [hl], 0
+    inc hl
+    ld [hl], 0
 
     ld a, 8
     ld hl, _OAM + 1
@@ -56,8 +70,85 @@ Player_Update::
     ld hl, keys
     ld b, [hl]
 
-    ; check for move right
+    ; check for jump
+    ld a, b
+    and BTN_UP
+    jr z, .update_jump
+
+    ; initialize jump state if not already jumping
+    ld hl, PLAYER_JUMPING
+    ld a, [hl]
+    or a
+    jr nz, .update_jump
+
+    ld [hl], 1
+
+    ld hl, PLAYER_VY
+    ld [hl], HIGH(INIT_VY)
+    inc hl
+    ld [hl], LOW(INIT_VY)
+
+.update_jump:
+    ld hl, PLAYER_JUMPING
+    ld a, [hl]
+    or a
+    jr z, .right
+
+    ; load y velocity into bc
+    ld hl, PLAYER_VY
+    ld b, [hl]
+    inc hl
+    ld c, [hl]
+
+    ; adjust velocity by gravity
+    ld a, c
+    sub LOW(GRAVITY)
+    ld c, a
     ld a, b
+    sbc HIGH(GRAVITY)
+    ld b, a
+
+    ld hl, PLAYER_VY
+    STORE16 bc
+
+    ; old_y = y
+    ld hl, PLAYER_Y
+    ld a, [hl]
+    ld hl, PLAYER_OLD_Y
+    ld [hl], a
+
+    ; y -= floor(vy)
+    ld hl, PLAYER_Y
+    ld a, [hl]
+    sub b
+    ld [hl], a
+
+    ; roll back jump if there was a collision
+    call player_bg_collides
+    jr nz, .update_jump_oam
+
+    ld hl, PLAYER_OLD_Y
+    ld a, [hl]
+    ld hl, PLAYER_Y
+    ld b, [hl]
+
+    ld hl, PLAYER_VY
+    ld [hl], 0
+
+    ; if colliding below, stop jump state
+    cp b
+    jr nc, .right
+
+    ld hl, PLAYER_JUMPING
+    ld [hl], 0
+
+.update_jump_oam:
+    call update_oam
+
+    ; check for move right
+.right:
+    ld hl, keys
+    ld a, [hl]
     and BTN_RIGHT
     jr z, .left
 
@@ -88,7 +179,8 @@ Player_Update::
 
 .left:
     ; check for left button
-    ld a, b
+    ld hl, keys
+    ld a, [hl]
     and BTN_LEFT
     ret z