From c71b612d0125c0aa0252c71e6b98db89f8716651 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Mon, 29 Jul 2019 20:46:06 +0800
Subject: [PATCH] add sierpinski_triangle

---
 examples/sierpinski_triangle.scad | 56 +++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 examples/sierpinski_triangle.scad

diff --git a/examples/sierpinski_triangle.scad b/examples/sierpinski_triangle.scad
new file mode 100644
index 00000000..ec6c9ada
--- /dev/null
+++ b/examples/sierpinski_triangle.scad
@@ -0,0 +1,56 @@
+include <line2d.scad>;
+include <turtle/turtle2d.scad>;
+
+module triangle(t, side_leng, width) {    
+    $fn = 48;
+    angle = 120; 
+    t_p1 = turtle2d("forward", t, side_leng);          
+    line2d(
+        turtle2d("pt", t), turtle2d("pt", t_p1), 
+        width, p1Style = "CAP_ROUND", p2Style =  "CAP_ROUND"
+    );    
+
+    t_p2 = turtle2d("forward", turtle2d("turn", t_p1, angle), side_leng);  
+    line2d(
+        turtle2d("pt", t_p1), turtle2d("pt", t_p2), 
+        width, p1Style = "CAP_ROUND", p2Style =  "CAP_ROUND"
+    ); 
+
+    t_p3 = turtle2d("forward", turtle2d("turn", t_p2, angle), side_leng);   
+    line2d(
+        turtle2d("pt", t_p2), turtle2d("pt", t_p3), 
+        width, p1Style = "CAP_ROUND", p2Style =  "CAP_ROUND"
+    );  
+}
+
+module two_triangles(t, side_len, len_limit, width) {
+    angle = 60;
+    triangle(t, side_len, width);
+    next_t = turtle2d("turn", turtle2d("forward", t, side_len / 2), angle); 
+    triangle(next_t, side_len / 2, width);
+}
+
+module sierpinski_triangle(t, side_len, len_limit, width) {
+    if(side_len >= len_limit) {
+        two_triangles(t, side_len, len_limit, width);
+
+        sierpinski_triangle(t, side_len / 2, len_limit, width);
+
+        sierpinski_triangle(
+            turtle2d("forward", t, side_len / 2), 
+            side_len / 2, len_limit, width
+        );
+
+        sierpinski_triangle(
+            turtle2d("turn", turtle2d("forward", turtle2d("turn", t, 60), side_len / 2), -60), 
+            side_len / 2, len_limit, width
+        );
+    }
+}
+
+side_len = 150;
+len_limit = 4;
+width = 0.5;
+t = turtle2d("create", 0, 0, 0);
+
+sierpinski_triangle(t, side_len, len_limit, width);
\ No newline at end of file