add filets

helper/math.scad

@@ -24,4 +24,28 @@ module mirror4XY(p, dx, dy) {
     children(0);
 }
 
+// Generate a 4x4 matrix that causes a change of basis
+// such that the origin is at point p0, the x axis is aligned
+// from p0 to p1 and point p2 is in the first quadrant.
+// Copied and pasted from https://trmm.net/Basis/
+module align_to(p0,p1,p2) {
+
+    x = unit(p1-p0);
+    yp = unit(p2-p0);
+    z = unit(cross(x,yp));
+    y = unit(cross(z,x));
+
+    echo(p0,p1,p2);
+    echo(x,y,z);
+
+    multmatrix([
+            [x[0], y[0], z[0], p0[0]],
+            [x[1], y[1], z[1], p0[1]],
+            [x[2], y[2], z[2], p0[2]],
+            [ 0,   0,    0,    1]
+        ])
+    children();
+}
+
+function unit(v) = v/norm(v);
 function lerp(a, b, t) = (b * t + a * (1 - t));