From 69976d834c2f581ec80b0a721280cb9cf180b2f1 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Thu, 29 Oct 2020 17:28:11 +0800
Subject: [PATCH] add catmull_rom_spline

---
 src/experimental/catmull_rom_spline.scad | 28 ++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 src/experimental/catmull_rom_spline.scad

diff --git a/src/experimental/catmull_rom_spline.scad b/src/experimental/catmull_rom_spline.scad
new file mode 100644
index 00000000..ad66aee5
--- /dev/null
+++ b/src/experimental/catmull_rom_spline.scad
@@ -0,0 +1,28 @@
+use <bezier_curve.scad>;
+
+function _catmull_rom_spline_4pts(t_step, points, tightness) = 
+    let(
+        p1x_0tightness = (points[2] - points[0]) / 4 + points[1],
+        v_p1x = points[1] - p1x_0tightness,
+        p1x = p1x_0tightness + v_p1x * tightness,
+        p2x_0tightness = (points[1] - points[3]) / 4 + points[2],
+        v_p2x = points[2] - p2x_0tightness,
+        p2x = p2x_0tightness + v_p2x * tightness
+    )
+    bezier_curve(t_step, [points[1], p1x, p2x, points[2]]);
+
+function catmull_rom_spline(t_step, points, tightness = 0) = 
+    let(
+        leng = len(points)
+    )
+    concat(
+        [
+            for(i = [0:leng - 4])
+                let(
+                    pts = _catmull_rom_spline_4pts(t_step, [for(j = [i:i + 3]) points[j]], tightness)
+                )
+                for(i = [0:len(pts) - 2]) pts[i]    
+        ],
+        [points[leng - 2]]
+    );
+    
\ No newline at end of file