From 2f1266e8c3116ce63a601ebf0f3136528a8c2666 Mon Sep 17 00:00:00 2001
From: Revar Desmera <revarbat@gmail.com>
Date: Mon, 27 Mar 2023 02:21:26 -0700
Subject: [PATCH] Corrected prismoid geometry corner anchor vectors.

---
 attachments.scad | 25 +++++++++++++++++++------
 vectors.scad     | 20 ++++++++++++++++++++
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/attachments.scad b/attachments.scad
index af62c38..5361964 100644
--- a/attachments.scad
+++ b/attachments.scad
@@ -2542,12 +2542,25 @@ function _find_anchor(anchor, geom) =
             bot = point3d(v_mul(point2d(size )/2, axy), -h/2),
             top = point3d(v_mul(point2d(size2)/2, axy) + shift, h/2),
             pos = point3d(cp) + lerp(bot,top,u) + offset,
-            vecs = [
-                if (anch.x!=0) unit(rot(from=UP, to=[(top-bot).x,0,h], p=[axy.x,0,0]), UP),
-                if (anch.y!=0) unit(rot(from=UP, to=[0,(top-bot).y,h], p=[0,axy.y,0]), UP),
-                if (anch.z!=0) anch==CENTER? UP : unit([0,0,anch.z],UP)
-            ],
-            vec = anchor==CENTER? UP : rot(from=UP, to=axis, p=unit(sum(vecs) / len(vecs))),
+            vecs = anchor==CENTER? [UP]
+              : [
+                    if (anch.x!=0) unit(rot(from=UP, to=[(top-bot).x,0,h], p=[axy.x,0,0]), UP),
+                    if (anch.y!=0) unit(rot(from=UP, to=[0,(top-bot).y,h], p=[0,axy.y,0]), UP),
+                    if (anch.z!=0) unit([0,0,anch.z],UP)
+                ],
+            vec2 = anchor==CENTER? UP
+              : len(vecs)==1? unit(vecs[0],UP)
+              : len(vecs)==2? vector_bisect(vecs[0],vecs[1])
+              : let(
+                    v1 = vector_bisect(vecs[0],vecs[2]),
+                    v2 = vector_bisect(vecs[1],vecs[2]),
+                    p1 = plane_from_normal(yrot(90,p=v1)),
+                    p2 = plane_from_normal(xrot(-90,p=v2)),
+                    line = plane_intersection(p1,p2),
+                    v3 = unit(line[1]-line[0],UP) * anch.z
+                )
+                unit(v3,UP),
+            vec = rot(from=UP, to=axis, p=vec2),
             pos2 = rot(from=UP, to=axis, p=pos)
         ) [anchor, pos2, vec, oang]
     ) : type == "conoid"? ( //r1, r2, l, shift
diff --git a/vectors.scad b/vectors.scad
index a654716..f588b82 100644
--- a/vectors.scad
+++ b/vectors.scad
@@ -284,6 +284,26 @@ function vector_axis(v1,v2=undef,v3=undef) =
             ) unit(cross(w1,w3));
 
 
+// Function: vector_bisect()
+// Usage:
+//   newv = vector_bisect(v1,v2);
+// Description:
+//   Returns a unit vector that exactly bisects the minor angle between two given vectors.
+//   If given two vectors that are directly opposed, returns `undef`.
+function vector_bisect(v1,v2) =
+    assert(is_vector(v1))
+    assert(is_vector(v2))
+    assert(!approx(norm(v1),0), "Zero length vector.")
+    assert(!approx(norm(v2),0), "Zero length vector.")
+    assert(len(v1)==len(v2), "Vectors are of different sizes.")
+    let( v1 = unit(v1), v2 = unit(v2) )
+    approx(v1,-v2)? undef :
+    let(
+        axis = vector_axis(v1,v2),
+        ang = vector_angle(v1,v2),
+        v3 = rot(ang/2, v=axis, p=v1)
+    ) v3;
+
 
 
 // Section: Vector Searching