particle simulation

particles-simulate.cljs

(ns saolsen.particles-simulate
  (:require [saolsen.draw-2d :as draw]))
;; Simple simulated neutonian physics.

(defn integrate-particle
  "Moves the particle a distance based on it's velocity
   P = P + V*dt
   Simple collisions with walls reverse velocity.
   Returns a new particle.
  "
  [world-width world-height particle]
  (let [pos (:pos particle)
        vel (:vel particle)
        new-pos (map + pos (map #(* 0.1 %) vel))
        [nx ny] new-pos
        collisions (cond
                    (or (< nx 0) (> nx world-width)) [-1 1]
                    (or (< ny 0) (> ny world-height)) [1 -1]
                    :else [1 1])
        new-vel (map * vel collisions)]
    (assoc particle :pos new-pos :vel new-vel)))

(defn main []
  (let [context (draw/get-canvas-context-from-id "draw")
        border {:type :line
                :color [0 0 0]
                :posns [[0 0] [500 0] [500 500] [0 500]]
                :width 5}
        span (take 6 (iterate (partial + 100) 40))
        particles (for [x span
                        y span]
                    {:type :circle
               	     :color [0 200 200]
	             :pos [x y]
	             :vel [(- (rand-int 100) 50)
                           (- (rand-int 100) 50)]
	             :size 5})
        integrater (partial integrate-particle
                            (:width context)
                            (:height context))
        worldstate (atom particles)]
    
    (defn update []
      (draw/request-animation-frame update)
      (swap! worldstate (partial map integrater))
      (draw/draw-scene (cons border @worldstate) context))
    
    (update)))

(main)