user can define his own xs

src/experimental/_impl/_pnoise1.scad

@@ -1,10 +1,10 @@
-function _pnoise1(x, n, slopes) =
+function _pnoise1(x, n, gradients) =
     let(
         lo = floor(x),
         hi = (lo + 1) % n,
         dist = x - lo,
-        loPos = slopes[lo] * dist,
-        hiPos = -slopes[hi] * (1 - dist),
+        loPos = gradients[lo] * dist,
+        hiPos = -gradients[hi] * (1 - dist),
         u = pow(dist, 3) * (dist * (dist * 6 - 15) + 10)
     )
     loPos * (1 - u) + hiPos * u;

src/experimental/pnoise1.scad

@@ -1,11 +1,13 @@
 use <experimental/_impl/_pnoise1.scad>  ;
 
-function pnoise1(from, to, step = 0.5) = 
+function pnoise1(xs, gradients) = 
     let(
+        from = floor(min(xs)),
+        to = ceil(max(xs)),
         n = to - from + 1,
-        slopes = rands(-1, 1, n)
+        grads = is_undef(gradients) ? rands(-1, 1, n) : gradients
     )
     [
-        for(x = [0:step:n - 1]) 
-        [from + x, _pnoise1(x, n, slopes)]
+        for(x = xs) 
+        _pnoise1(x, n, grads)
     ];