From 078f9eb929de8ea8fdc983a5950fb26ff631f1ed Mon Sep 17 00:00:00 2001
From: Ethan Dalool <git@voussoir.net>
Date: Mon, 13 Sep 2021 18:57:29 -0700
Subject: [PATCH] Add dovetails.scad.

---
 voussoir/dovetails.scad | 76 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 voussoir/dovetails.scad

diff --git a/voussoir/dovetails.scad b/voussoir/dovetails.scad
new file mode 100644
index 0000000..b204a48
--- /dev/null
+++ b/voussoir/dovetails.scad
@@ -0,0 +1,76 @@
+ZFIGHT = 0.001;
+
+module dovetails(dovetail_width, dovetail_height, count, clearance)
+{
+    centering = ((count-1) * dovetail_width / 2);
+    for (index=[0:count-1])
+    {
+        x_off = (index * dovetail_width) - centering;
+        translate([x_off, 0])
+        intersection()
+        {
+            trapezoid(
+                upper_width=(dovetail_width * 2 / 3 - clearance),
+                lower_width=(dovetail_width * 1 / 3 - clearance),
+                height=dovetail_height
+            );
+
+            // Masks off the clearance from the top side.
+            translate([0, -clearance/2])
+            square([dovetail_width, dovetail_height - clearance], center=true);
+        }
+    }
+}
+
+module dovetail_block(block_width, block_height, dovetail_width, dovetail_height, clearance=0)
+{
+    module mask()
+    {
+        square([block_width, block_height], center=true);
+    }
+    module main_block()
+    {
+        w = block_width;
+        h = block_height - (2 * dovetail_height);
+        square([w, h], center=true);
+    }
+    module upper_dovetails()
+    {
+        count = ceil(block_width / dovetail_width);
+        y = (block_height - dovetail_height) / 2;
+        translate([0, y - ZFIGHT])
+        dovetails(dovetail_width, dovetail_height, count, clearance);
+    }
+    module lower_dovetails()
+    {
+        count = ceil(block_width / dovetail_width) + 1;
+        y = (block_height - dovetail_height) / 2;
+        translate([0, -(y - ZFIGHT)])
+        mirror([0, 1])
+        dovetails(dovetail_width, dovetail_height, count, clearance);
+    }
+    intersection()
+    {
+        union()
+        {
+            main_block();
+            upper_dovetails();
+            lower_dovetails();
+        }
+
+        mask();
+    }
+}
+
+module trapezoid(upper_width, lower_width, height)
+{
+    x1 = upper_width / 2;
+    x2 = lower_width / 2;
+    y1 = height / 2;
+    polygon([
+        [-x1, y1],
+        [x1, y1],
+        [x2, -y1],
+        [-x2, -y1]
+    ]);
+}