From 933b2d9d73ce1008a727065676d5cfc0612231ca Mon Sep 17 00:00:00 2001
From: zhao <zhao@zhaos-MacBook-Pro.local>
Date: Thu, 12 Jan 2023 00:28:36 -0500
Subject: [PATCH] add halfspace

---
 helper/common.scad    |  2 +-
 helper/halfspace.scad | 16 ++++++++++++++--
 helper/math.scad      |  9 +++++++++
 helper/rotation.scad  |  3 ---
 4 files changed, 24 insertions(+), 6 deletions(-)
 delete mode 100644 helper/rotation.scad

diff --git a/helper/common.scad b/helper/common.scad
index dc0c2d7..2fb5f4e 100644
--- a/helper/common.scad
+++ b/helper/common.scad
@@ -3,7 +3,7 @@
 */
 
 $fn=64;
-
+// TODO move these to math
 eps=0.0001;
 
 inf10 = 10;
diff --git a/helper/halfspace.scad b/helper/halfspace.scad
index 4553fe5..503a0a1 100644
--- a/helper/halfspace.scad
+++ b/helper/halfspace.scad
@@ -1,2 +1,14 @@
-// TODO
-// probably want to get rotations first
\ No newline at end of file
+
+// Wake up sheeple. Halfspaces are just really BIG cubes!
+include <./math.scad>
+include <./common.scad>
+
+module halfspace(vpos, p) {
+    translate(p)
+    align(a=[0,0,1], b=vpos)
+    translate(v=[0,0,-inf/2])
+        cube(size=[inf, inf, inf], center=true);
+}
+
+
+halfspace(vpos=[1,1,1], p=[10,10,10]);
\ No newline at end of file
diff --git a/helper/math.scad b/helper/math.scad
index 9c13773..da7373d 100644
--- a/helper/math.scad
+++ b/helper/math.scad
@@ -10,3 +10,12 @@ function mirror4XY(midpoint, offsetX, offsetY)  =
         [midpoint[0]-offsetX, midpoint[1]+offsetY, midpoint[2]],
         [midpoint[0]-offsetX, midpoint[1]-offsetY, midpoint[2]],
         [midpoint[0]+offsetX, midpoint[1]-offsetY, midpoint[2]]];
+
+
+module align(a,b) {
+    rot_axis = cross(a,b);
+    angle = acos(a*b/ (norm(a)*norm(b)));
+
+    rotate(v=rot_axis, a=angle)
+        children(0);
+}
diff --git a/helper/rotation.scad b/helper/rotation.scad
deleted file mode 100644
index 91a6e70..0000000
--- a/helper/rotation.scad
+++ /dev/null
@@ -1,3 +0,0 @@
-// TODO
-
-// eg transformation to rotate vector a to vector b, etc
\ No newline at end of file