add help

1 files changed, 1 insertions, 0 deletions

diff --git a/js/util.js b/js/util.js
index f071596..e4c50dc 100644
--- a/js/util.js
+++ b/js/util.js
@@ -36,6 +36,7 @@ function randint(n){ return rand(n)|0 }
 function choice(a){ return a[randint(a.length)] }
 function deg(n){ return n*180/PI }
 function rad(n){ return n*PI/180 }
+function pixel(x,y){ return 4*(y*w+x) }
 
 function step (n,a,b) {
   return clamp((n - a) / (b - a), 0.0, 1.0);