From 6cd73c7323ed38bf05dc69e6cf860cf9a59b587f Mon Sep 17 00:00:00 2001
From: Chris Hodapp <hodapp87@gmail.com>
Date: Sun, 12 Jul 2020 13:09:36 -0400
Subject: [PATCH] Little refactor (WIP), more mouse interaction

---
 README.md               |  10 ++--
 src/curlnoise/core.cljc | 100 +++++++++++++++++++++++++++-------------
 2 files changed, 72 insertions(+), 38 deletions(-)

diff --git a/README.md b/README.md
index 405d80f..33b6646 100644
--- a/README.md
+++ b/README.md
@@ -31,13 +31,9 @@ to run the ClojureScript version in the browser.
 
 - Better docs.
 - Make things more interactive, e.g. let the user place obstacles.
-- Factor out the potential function rather than burying it in
-  `update-state`.
 - Visualize amplitude function & potential function.  I have
   `draw-field` which `show-fn` enables, but it is rudimentary.
-- Figure out reasonable boundary behavior.  I'd like to do toroidal,
-  but I would need to gradually blend the potential function at the
-  edges for this to work right (otherwise particles are just stuck at
-  the boundaries due to the discontinuity).
 - Use 'real' simplex or OpenSimplex noise implementation that has a
-  gradient instead of doing it numerically?
+  gradient instead of doing it numerically.
+- Add multi-octave noise and look into what the paper says about
+  turbulence.  (Look up 'advection' technique it mentions too.)
diff --git a/src/curlnoise/core.cljc b/src/curlnoise/core.cljc
index 76c0422..f14a5b8 100644
--- a/src/curlnoise/core.cljc
+++ b/src/curlnoise/core.cljc
@@ -6,9 +6,9 @@
 (def res-x 500)
 (def res-y res-x)
 ;; Number of particles to use:
-(def particles 2000)
+(def particles 1000)
 ;; Lower alpha produces *longer* particle trails
-(def alpha 40)
+(def alpha 30)
 
 (def renderer #?(:clj  :java2d
                  :cljs :p2d))
@@ -56,32 +56,70 @@
         l  (+ (dist (max 0.0 dx) (max 0.0 dy)) (min (max dx dy) 0.0))]
     l))
 
+
+;; Domain scale for noise function:
+(def scale 500.0)
+;; Amplitude multiplier for noise:
+(def noise-scale (* scale 5.0))
+
+(def f-inv (/ scale))
+;; Potential function (2D + time):
+(defn potential [x y t]
+  "2D (+ time) potential function. Returns a scalar.
+
+  The absolute value of the scalar doesn't matter, but its gradient of
+  determines particle velocity. "
+  (* noise-scale
+     (+ (q/noise (* f-inv x) (* f-inv y) (* f-inv t))
+        (q/noise (* f-inv x 2.0) (* f-inv y 2.0) (* f-inv t 1.61))
+        )))
+;; 1.61 is sort of arbitrarily chosen so that periods of the octaves
+;; don't line up exactly
+
+;; Delta used for 'gradient'. Multiplying screen width/height by 1e-3
+;; to 1e-4 usually gives an acceptable value.
+(def eps 0.5)
+(def eps-inv (/ eps))
+
+(defn gradient [p-fn x y t]
+  "Numerical gradient of potential function 'p-fn' via finite differences.
+
+  'p-fn' should be a function that takes 3 arguments - (x,y,t) - and
+  returns a scalar for the potential at that position and time.
+
+  Returns [d/dx, d/dy] of 'p-fn' at (x, y, t)."
+  (let [p      (p-fn x         y         t)
+        p-dx   (p-fn (+ x eps) y         t)
+        p-dy   (p-fn x         (+ y eps) t)
+        grad-x (* (- p-dx p) eps-inv)
+        grad-y (* (- p-dy p) eps-inv)]
+    [grad-x grad-y]))
+
+(defn move-point [x y]
+  "Move a particle by the potential at a point.
+
+  Returns [x y] of the 'updated' point."
+  )
+
 (defn update-state [state]
   (let [w (q/width)
         h (q/height)
         ;; Overall multiplier for velocity of particle:
         vf 0.1
-        ;; Domain scale for noise function:
-        scale 500.0
-        ;; Amplitude multiplier for noise:
-        noise-scale (* scale 10.0)
         ;; Radius for mouse-thingy:
         rad 20.0
         ;; Radius for rounded corners:
         rect-rad 100.0
         margin 0
-        eps (* w 1e-3)
         mx (q/mouse-x)
         my (q/mouse-y)
-        f-inv (/ scale)
         ;; "width of the modified region":
-        d0 150.0
+        d0 200.0
         ;; distance of point to a circle of radius 'rad'
         ;; centered at mouse cursor:
         d-mouse #(if (q/mouse-pressed?)
                    (- (dist (- mx %1) (- my %2)) rad)
-                   1e6 ;; arbitrarily large value
-                   )
+                   1e6)
         ;; function for distance to the border:
         d-border #(- rect-rad
                      (sdf-box (- %1 rect-rad) ; x
@@ -90,20 +128,17 @@
                               (- h (* rect-rad 2)) ; height
                               ))
         ;; potential modulation function - takes (x,y):
-        amp-fn (fn [_ _] 1.0)
+        amp-fn (fn [x y] (ramp (/ (d-mouse x y) d0)))
         ;; #(ramp (min (/ (d-mouse %1 %2) d0)
         ;;             (/ (d-border %1 %2) d0)
         ;;             ))
-        mouse-drift #(if (q/mouse-pressed?)
+        mouse-drift #(if (or (< mx 0) (< my 0) (> mx w) (> my h))
+                       0.0
                        (+ 
-                        (* (- (/ mx w) 0.5) %2 0.01)
-                        (* (- (/ my h) 0.5) %1 -0.01))
-                       0.0)
+                        (* (- (/ mx w) 0.5) %2 20)
+                        (* (- (/ my h) 0.5) %1 -20)))
         ;; Noise function - must take 3 arguments, (x,y,z):
-        n-fn #(* noise-scale
-                 (+
-                  (mouse-drift %1 %2)
-                  (q/noise (* f-inv %1) (* f-inv %2) (* f-inv %3))))
+        n-fn #(+ (mouse-drift %1 %2) (potential %1 %2 %3))
         ;; Overall amplitude function:
         p-fn #(* vf (amp-fn %1 %2) (n-fn %1 %2 %3))
         points
@@ -113,25 +148,28 @@
                      border (if (and (and (> x margin) (< x (- w margin)))
                                      (and (> y margin) (< x (- h margin))))
                               1.0 0.0)
-                     ;; Potential at (x, y, z):
-                     n (p-fn x y z)
-                     n-dx (p-fn (+ x eps) y z)
-                     n-dy (p-fn x (+ y eps) z)
-                     ;; Velocity by finite differences:
-                     vx (/ (- n-dy n) eps)
-                     vy (/ (- n n-dx) eps)
-                     ;; Updated point position:
-                     x2 (+ x vx)
-                     y2 (+ y vy)
+
+                     f #(* vf
+                           (+ (mouse-drift %1 %2)
+                              (* (potential %1 %2 %3)
+                                 (amp-fn %1 %2))))
+                     [gx gy] (gradient f x y z)
+                     
+                     ;; Update points (move perpendicular to gradient):
+                     x2 (+ x gy)
+                     y2 (- y gx)
                      [x3 y3] (if (or (< x2 0) (> x2 w) (< y2 0) (> y2 h))
                                [(q/random w) (q/random h)]
                                [x2 y2])
                      ;; This boundary behavior is a little more
                      ;; interesting: when a particle leaves the edges,
                      ;; it just reappears in a random place.
+                     [x4 y4] (if (and (q/mouse-pressed?) (< (dist (- mx x) (- my y)) rad))
+                               [(q/random w) (q/random h)]
+                               [x3 y3])
                      ]
                  
-                 [x3 y3]
+                 [x4 y4]
                  )) (:grid state))]
     (-> state
         (update :frame inc)