Add aphorism thirty-five: middle-point of a linestring

src/aphorisms/thirty_five.clj

@@ -0,0 +1,60 @@
+(ns aphorisms.thirty-five
+  (:require [quil.core :as q]
+            [quil.middleware :as qm]
+            [thi.ng.geom.core :as g]
+            [thi.ng.geom.line :as l]
+            [thi.ng.geom.rect :as r]
+            [thi.ng.geom.vector :as v]))
+
+;; Small experiment to find the central point along a line string;
+;; Turns out this is as easy as calling (g/point-at l 0.5) on a non-empty line :)
+
+(def bounds (r/rect 500 500))
+
+(defn setup []
+  (q/ellipse-mode :center)
+  (q/rect-mode :corners)
+  (q/color-mode :hsb 255)
+  {:current-line (l/linestrip2 [])})
+
+(defn mouse-pressed [state ev]
+  (prn state)
+  (if (= (:button ev) :right)
+    ;; clear on right-click
+    (assoc state :current-line (l/linestrip2 []))
+    (update-in state [:current-line :points] conj (v/vec2 (:x ev) (:y ev)))))
+
+(defn draw-state [state]
+  (q/background 255 0 255)
+  (q/no-fill)
+  (q/stroke 255 120 220)
+  (q/stroke-weight 1)
+  ;; draw lines between points
+  (doseq [[[x1 y1] [x2 y2]] (->>
+                             (interleave (-> state :current-line :points) (rest (-> state :current-line :points)))
+                             (partition 2))]
+    (q/line x1 y1 x2 y2))
+  ;; draw points
+  (q/stroke 255 0 255)
+  (q/stroke-weight 2)
+  (q/fill  255 255 220)
+  (doseq [[x y] (-> state :current-line :points)]
+    (q/ellipse x y 5 5))
+  ;; draw center point
+  (when (seq (-> state :current-line :points))
+    (let [[cx cy] (g/point-at (:current-line state) 0.5)]
+      (q/ellipse cx cy 10 10))))
+
+#_:clj-kondo/ignore
+(q/defsketch thirty-five
+  :title "Thirty-Five"
+  :size (:size bounds)
+  :settings #(q/pixel-density (q/display-density))
+  :features [:keep-on-top]
+  :setup setup
+  :mouse-pressed mouse-pressed
+  :update identity
+  :draw draw-state
+  :middleware [qm/pause-on-error #_(screenshottable) qm/fun-mode])
+
+(defn -main [& _args])