From 704c2b6c947efdd7e3a717ef2d0de93f322fbd53 Mon Sep 17 00:00:00 2001
From: Fay Carsons <faycarsons23@gmail.com>
Date: Wed, 13 Dec 2023 04:49:18 -0500
Subject: [PATCH] Circle packing example (#72)

* circle packing example first draft

* added concentric circles

* refactored to fix type issues, added more comments, parameter tweaks
---
 examples/circle_packing.ml | 109 +++++++++++++++++++++++++++++++++++++
 examples/dune              |   5 ++
 lib/shape.mli              |   1 +
 3 files changed, 115 insertions(+)
 create mode 100644 examples/circle_packing.ml

diff --git a/examples/circle_packing.ml b/examples/circle_packing.ml
new file mode 100644
index 0000000..f75389d
--- /dev/null
+++ b/examples/circle_packing.ml
@@ -0,0 +1,109 @@
+open Joy.Shape
+
+(* global constants // RNG initialization *)
+let resolution = (1200, 900)
+let min_radius = 20
+let max_radius = 150
+let num_circles = 5_000
+let max_attempts = 100_000
+let shrink_factor = 0.85
+let _ = Stdlib.Random.self_init ()
+
+let palette =
+  [
+    (* purple *)
+    (107, 108, 163);
+    (* light blue *)
+    (135, 188, 189);
+    (* green *)
+    (111, 153, 84);
+    (* light purple *)
+    (150, 155, 199);
+    (* light green *)
+    (137, 171, 124);
+    (* dark purple *)
+    (67, 68, 117);
+    (* darker purple *)
+    (44, 45, 84);
+  ]
+
+(* utility Functions *)
+
+(* distance between two points *)
+let distance (x1, y1) (x2, y2) =
+  let dx = float_of_int x2 -. float_of_int x1 in
+  let dy = float_of_int y2 -. float_of_int y1 in
+  let dist = sqrt ((dx *. dx) +. (dy *. dy)) in
+  int_of_float dist
+
+(* determines if two circles overlaps *)
+let overlaps (p1, r1) (p2, r2) =
+  let dist = distance p1 p2 in
+  dist < r1 + r2
+
+(* creates a random point within screen bounds *)
+let rand_point () =
+  ( Stdlib.Random.full_int (fst resolution * 2) - fst resolution,
+    Stdlib.Random.full_int (snd resolution * 2) - snd resolution )
+
+(* creates a circle with a random center point and radius *)
+let rand_circle () =
+  let point = rand_point () in
+  (point, min_radius + Stdlib.Random.full_int (max_radius - min_radius))
+
+(* creates a lis of packed circles *)
+let pack_circles () =
+  (* checks whether a circle intersects with a list of circles *)
+  let check_overlaps lst current =
+    List.fold_right (fun curr acc -> overlaps curr current || acc) lst false
+  in
+  (* creates a new circle, checks if it intersects previous circles,
+     if max attempts have been reached,
+     or if the desired number of circles have been created.
+     From there it either recurses with or without the new circle,
+     or returns the list of circles *)
+  let rec pack lst attempts =
+    let new_circle = rand_circle () in
+    let does_overlap = check_overlaps lst new_circle in
+    let safe = List.length lst < num_circles - 1 && attempts < max_attempts in
+    if does_overlap && safe then pack lst (attempts + 1)
+    else if not safe then new_circle :: lst
+    else pack (new_circle :: lst) attempts
+  in
+  let attempts = 0 in
+  let lst = [ rand_circle () ] in
+  pack lst attempts
+
+(* pulls a random color from the 'palette' list
+   sets draw color with it
+   then draws circle *)
+let draw_with_color circle =
+  let idx = Stdlib.Random.full_int (List.length palette - 1) in
+  let r, g, b = List.nth palette idx in
+  Graphics.set_color (Graphics.rgb r g b);
+  render_shape circle
+
+(* turns a circle into a list of concentric circles *)
+let make_concentric circle =
+  let rec shrink lst =
+    let point, radius = List.hd (List.rev lst) in
+    if radius <= 1 then lst
+    else
+      let new_circle =
+        (point, int_of_float (float_of_int radius *. shrink_factor))
+      in
+      shrink (lst @ [ new_circle ])
+  in
+  shrink [ circle ]
+
+(* main fn *)
+let () =
+  set_dimensions (fst resolution) (snd resolution);
+  init ();
+  Graphics.set_line_width 3;
+  let circles = pack_circles () in
+  let circles = List.flatten (List.map make_concentric circles) in
+  List.iter
+    (fun ((x, y), radius) -> draw_with_color (circle ~x ~y radius))
+    circles;
+  close ()
diff --git a/examples/dune b/examples/dune
index 27ea231..b07fb75 100644
--- a/examples/dune
+++ b/examples/dune
@@ -97,3 +97,8 @@
  (name complex)
  (modules complex)
  (libraries joy))
+
+(executable
+ (name circle_packing)
+ (modules circle_packing)
+ (libraries joy))
diff --git a/lib/shape.mli b/lib/shape.mli
index db854a6..99c216f 100644
--- a/lib/shape.mli
+++ b/lib/shape.mli
@@ -1,6 +1,7 @@
 type point
 type shape
 type shapes = shape list
+type point = { x : int; y : int }
 
 val render_shape : shape -> unit
 val point : int -> int -> point