Use cached stencil functions, add opts.buffer

README.md

@@ -27,6 +27,8 @@ Takes an ndarray and prepares it for cave generation. Options include:
 * `iterations`: The amount of iterations to apply immediately. Defaults to 0.
 * `border`: If truthy, will include a solid border around the results.
   Defaults to 1.
+* `buffer`: An ndarray buffer to use between iterations, which must be the same
+  shape as the original array. If none is supplied, one will be created.
 
 Note that this function will modify the array directly.
 

index.js

@@ -4,20 +4,49 @@ var fill = require('ndarray-fill')
 var zero = require('zeros')
 
 var neighbors = neighborhood.length
+var stencils = {}
 
 module.exports = generate
+
+// ndarray-stencil generates code using cwise, and as
+// such incurs a slight performance hit initially.
+// To work around this, we can keep two cached functions
+// which use shared parameters. See `iterator` for more info.
+var sharedWidth = null
+var sharedHeight = null
+var sharedBorder = null
+var sharedThreshold = null
+
+stencils.vanilla = stencil(neighborhood, function(p1,p2,p3,p4,p5,p6,p7,p8,p9,pos) {
+  return (
+    p1+p2+p3+p4+p5+p6+p7+p8+p9 >= sharedThreshold
+  ) ? 1 : 0
+}, { useIndex: false })
+
+stencils.border = stencil(neighborhood, function(p1,p2,p3,p4,p5,p6,p7,p8,p9,pos) {
+  return (
+    p1+p2+p3+p4+p5+p6+p7+p8+p9 >= sharedThreshold ||
+    pos[0] < sharedBorder ||
+    pos[0] > sharedWidth - sharedBorder - 3 ||
+    pos[1] < sharedBorder ||
+    pos[1] > sharedHeight - sharedBorder - 3
+  ) ? 1 : 0
+}, { useIndex: true })
+
 function generate(array, opts) {
   opts = opts || {}
 
   var width = array.shape[0]
     , height = array.shape[1]
-    , buffer = zero([ width, height ])
+    , buffer = opts.buffer || zero([ width, height ])
 
   var density = opts.density || 0.5
     , threshold = opts.threshold || 5
     , border = 'border' in opts ? opts.border : 1
-    , hood = opts.hood || 1
     , shouldFill = 'fill' in opts ? opts.fill : true
+    , iterate = stencils[
+      border ? 'border' : 'vanilla'
+    ]
 
   if (shouldFill) fill(array, function(x, y) {
     return Math.random() <= density || (
@@ -26,27 +55,23 @@ function generate(array, opts) {
     ) ? 1 : 0
   })
 
-  var iterate = border ? stencil(neighborhood, function(p1,p2,p3,p4,p5,p6,p7,p8,p9,pos) {
-    return (
-      p1+p2+p3+p4+p5+p6+p7+p8+p9 >= threshold ||
-      pos[0] < border ||
-      pos[0] > width - border - 3 ||
-      pos[1] < border ||
-      pos[1] > height - border - 3
-    ) ? 1 : 0
-  }, { useIndex: true }) : stencil(neighborhood, function(p1,p2,p3,p4,p5,p6,p7,p8,p9,pos) {
-    return (
-      p1+p2+p3+p4+p5+p6+p7+p8+p9 >= threshold
-    ) ? 1 : 0
-  }, { useIndex: true })
-
   if (opts.iterations) {
     iterator(opts.iterations)
   }
 
   return iterator
 
+  // Updates the shared variables that are available
+  // on the module-level scope. This is a synchronous
+  // operation, so it's totally safe (though not
+  // necessarily pretty) provided these values are
+  // updated before any iteration.
   function iterator(iterations) {
+    sharedWidth = width
+    sharedHeight = height
+    sharedBorder = border
+    sharedThreshold = threshold
+
     iterations = iterations || 1
 
     for (var i = 0; i < iterations; i += 1) {