From 5af28d860ed9cc348cafcd7dc56cf52d502ebf18 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johan=20Hillerstr=C3=B6m?= <progr@mmer.nu>
Date: Sat, 21 Nov 2015 02:26:50 +0100
Subject: [PATCH] Update vibratopos according to the spec

---
 xmeffects.js | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xmeffects.js b/xmeffects.js
index dad153d..7249bc7 100644
--- a/xmeffects.js
+++ b/xmeffects.js
@@ -71,8 +71,11 @@ function eff_t1_4(ch) {  // vibrato
         ch.vibratopos, ch.vibratospeed, ch.vibratodepth);
     ch.periodoffset = 0;
   }
-  ch.vibratopos += ch.vibratospeed;
-  ch.vibratopos &= 63;
+  // only updates on non-first ticks
+  if (player.cur_tick > 0) {
+    ch.vibratopos += ch.vibratospeed;
+    ch.vibratopos &= 63;
+  }
 }
 
 function getVibratoDelta(type, x) {