Add color support to Mathbox surfaces

[sritchie]

emmy.mathbox.colors:

(ns emmy.mathbox.colors
  "Borrowed from
  https://github.com/ChristopherChudzicki/math3d-react/blob/master/client/src/constants/colors.js"
  (:require ["three" :as three]))

(def colors
  ["#33FF00"
   "#2ecc71"
   "#3498db"
   "#9b59b6"
   "#8e44ad"
   "#2c3e50"
   "#f1c40f"
   "#e67e22"
   "#e74c3c"
   "#808080"])

(def color-maps
  {:rainbow
   {:css "background: linear-gradient(
      to right,
      hsl(360, 100%, 50%),
      hsl(300, 100%, 50%),
      hsl(240, 100%, 50%),
      hsl(180, 100%, 50%),
      hsl(120, 100%, 50%),
      hsl(60, 100%, 50%),
      hsl(0, 100%, 50%)
    )
    "
    :f (fn [frac]
         (let [color (three/Color. 0xffffff)]
           (.setHSL (- 1 frac) 1 0.5)
           [(.-r color) (.-g color) (.-b color)]))}
   :bluered
   {:css "background: linear-gradient(to right, blue, red)"
    :f (fn [frac]
         [frac 0 (- 1 frac) 1])}
   :temperature
   {:css "background: linear-gradient(
      to right,
      hsl(240, 100%, 50%),
      hsl(180, 100%, 50%),
      hsl(120, 100%, 50%),
      hsl(60, 100%, 50%),
      hsl(0, 100%, 50%)
    )
    "
    :f (fn [frac]
         (let [color (three/Color. 0xffffff)]
           (.setHSL (* 0.666 (- 1 frac)) 1 0.5)
           [(.-r color) (.-g color) (.-b color)]))}})

Here is the start of my modificaiton to Surface2D:

(defn true-params-fn [[u-min u-max] [v-min v-max]]
  (let [du (- u-max u-min)
        dv (- v-max v-min)]
    (fn [u v]
      [(+ u-min (* u du))
       (+ v-min (* v dv))])))

[mb/Area
      {:axes (:axes opts)
       :live false
       :items 1
       :channels 4
       :width width
       :height height
       :rangeX (:rangeX opts [0 1])
       :rangeY (:rangeY opts [0 1])
       :expr (let [{:keys [css f]} (:rainbow c/color-maps)
                   true-params (true-params-fn rangeX rangeY)]
               (fn [emit x y i j]
                 (let [[trueU trueV] (true-params x y)]
                   (expr (fn [x y z]
                           )
                         x y i j))
                 (emit x y i j)))}]