Add halston sequence example to random-points

src/shimmers/algorithm/random_points.cljc

@@ -1,6 +1,7 @@
 (ns shimmers.algorithm.random-points
   (:require
    [shimmers.algorithm.poisson-disc-sampling :as pds]
+   [shimmers.math.core :as sm]
    [shimmers.math.deterministic-random :as dr]
    [thi.ng.geom.circle :as gc]
    [thi.ng.geom.core :as g]
@@ -68,8 +69,35 @@
             (reset! pool (if (seq r) r (dr/shuffle points)))
             v))))
 
+;; https://observablehq.com/@jrus/halton
+(defn halton [index base]
+  (loop [index index
+         fraction 1
+         result 0]
+    (if (<= index 0)
+      result
+      (let [fract (/ fraction base)]
+        (recur (Math/floor (/ index base))
+               fract
+               (+ result (* fract (mod index base))))))))
+
+(comment (for [i (range 32)]
+           (halton i 7)))
+
+;; how to pick good prime pairs?
+(defn halton-prime-pair [lower upper]
+  (let [primes (sm/primes-between lower upper)
+        p1 (dr/rand-nth primes)]
+    [p1 (dr/rand-nth (remove #{p1 (+ p1 2) (- p1 2)} primes))]))
+
+(defn halton-sequence [bounds [p1 p2] n]
+  (for [i (range n)
+        :let [k (+ i 100)]]
+    (g/unmap-point bounds (gv/vec2 (halton k p1) (halton k p2)))))
+
 (def modes
   {:random-points random-points
    :random-cells random-cells
    :random-cell-jitter random-cell-jitter
-   :poisson-disc-sampling poisson-disc-sampling} )
+   :poisson-disc-sampling poisson-disc-sampling
+   :halton-sequence halton-sequence} )

src/shimmers/sketches/random_point_field.cljs

@@ -4,6 +4,7 @@
    [shimmers.algorithm.random-points :as rp]
    [shimmers.common.svg :as csvg]
    [shimmers.common.ui.controls :as ctrl]
+   [shimmers.common.ui.debug :as debug]
    [shimmers.math.graph :as graph]
    [shimmers.sketch :as sketch :include-macros true]
    [shimmers.view.sketch :as view-sketch]
@@ -46,7 +47,10 @@
   (let [bounds (g/scale-size (rect/rect 0 0 width height) 0.99)
         {:keys [mode n-points mst]} @ui-state
         point-cloud (get rp/modes mode)
-        points (point-cloud bounds (or n-points 1))]
+        primes (rp/halton-prime-pair 20 60)
+        points (if (= mode :halton-sequence)
+                 (point-cloud bounds primes (* n-points 4))
+                 (point-cloud bounds (or n-points 1)))]
     [:div
      [:div.canvas-frame [scene points mst]]
      [:div.explanation.contained
@@ -59,6 +63,8 @@
         [:h4 "Controls"]
         (ctrl/change-mode ui-state (keys rp/modes))
         (ctrl/numeric ui-state "Generated Points" [:n-points] [2 1024 1])
+        (when (= mode :halton-sequence)
+          [:div "Halton sequence from co-primes " (debug/pre-edn primes)])
         (ctrl/checkbox ui-state "Show MST Circles" [:mst])]]]]))
 
 (sketch/definition random-point-field