add slide function

lights.js

@@ -9,6 +9,7 @@ const log = new Logger(
 );
 
 const fade_ticks = cfg.fade_ticks || 20;
+var num_ticks = 0;
 var pixels = new Uint32Array(cfg.leds);
 var pixel_cache = new Uint32Array(cfg.leds);
 var next_pattern = new Uint32Array(cfg.leds);
@@ -113,15 +114,25 @@ export const functions = {
       convert_args: true,
     }
   ),
-  slide: new Function(
+  stagger: new Function(
     (index, arg1, arg2) => {
-      return index + arg2;
+      return (index + arg2) % 255;
     },
     {
       requires_arg1: true,
       requires_arg2: true,
       convert_args: true,
-    }
+    },
+    slide: new Function(
+      (index, arg1, arg2) => {
+        return (num_ticks + arg2) % 255;
+      },
+      {
+        requires_arg1: true,
+        requires_arg2: true,
+        convert_args: true
+      }
+    )
   ),
 };
 
@@ -171,6 +182,7 @@ function tick_pattern() {
   } else {
     getRandom();
   }
+  num_ticks++;
 }
 
 function getRandom() {