From 424b80e28ce3e9993d88f66a6ee68418a0fca46c Mon Sep 17 00:00:00 2001
From: Forest Belton <65484+forestbelton@users.noreply.github.com>
Date: Tue, 20 Jul 2021 18:02:01 -0400
Subject: [PATCH] Cap velocity at 7px/frame

---
 inc/util.inc |  9 +++++++++
 src/player.s | 16 +++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/inc/util.inc b/inc/util.inc
index d67cce3..4d381c6 100644
--- a/inc/util.inc
+++ b/inc/util.inc
@@ -77,3 +77,12 @@ MACRO CP16
     cp LOW(\1)
 .done\@
 ENDM
+
+; A = MIN(A, x)
+; \1 Other value
+MACRO MIN
+    cp \1
+    jr c, .skip\@
+    ld a, \1
+.skip\@:
+ENDM
diff --git a/src/player.s b/src/player.s
index a98dc1a..839e913 100644
--- a/src/player.s
+++ b/src/player.s
@@ -32,7 +32,8 @@ DEF TILE_SIZE EQU 16 ; Total length of tile in bytes
 
 DEF GRAVITY EQU (0 << 8) | $2e ; 0.18
 DEF INIT_VY EQU (3 << 8) | $99 ; 3.60
-DEF INIT_FALL_VY EQU ($ff << 8) | $1a ; a.b
+DEF INIT_FALL_VY EQU ($ff << 8) | $1a ; -1.1015625
+DEF MAX_VY EQU ($f9 << 8) | $00 ; -7.0
 
 Player_Init::
     ; Clear player data (X/Y initialized by map engine)
@@ -91,6 +92,19 @@ Player_Update::
     sbc HIGH(GRAVITY)
     ld b, a
 
+    ; we only need to clamp when moving down
+    bit 7, b
+    jr z, .no_clamp
+
+    ; vy = MIN(MAX_VY, vy)
+    ld a, b
+    cp HIGH(MAX_VY)
+    jr c, .no_clamp
+
+    ld b, HIGH(MAX_VY)
+    ld c, LOW(MAX_VY)
+
+.no_clamp:
     ld hl, PLAYER_VY
     STORE16 bc