add halfspace

helper/common.scad

@@ -3,7 +3,7 @@
 */
 
 $fn=64;
-
+// TODO move these to math
 eps=0.0001;
 
 inf10 = 10;

helper/halfspace.scad

@@ -1,2 +1,14 @@
-// TODO
-// probably want to get rotations first
+
+// 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]);

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);
+}

helper/rotation.scad

@@ -1,3 +0,0 @@
-// TODO
-
-// eg transformation to rotate vector a to vector b, etc