Refactor prisms for scheme (#35)

* implement geom_fix_object for prisms (recompute centroid of polygon floor from center of geometric object); update test-prism to displace objects through random 3D vector

* updates

* refactor make_prism() to facilitate handling of prisms in scheme

* refactor prism implementation for compatibility with legacy scheme interface

* updates

* updates

* fix commented-out code

* use random sentinel for no-val

* use same NO_VAL as in scm

* use nan instead of no-val

* use nan for auto-center

Author: Homer Reid

utils/ctlgeom.h

@@ -51,7 +51,7 @@ extern void display_geometric_object_info(int indentby, geometric_object o);
 #endif
 
 extern void geom_initialize(void);
-extern void geom_fix_object(GEOMETRIC_OBJECT o);
+extern void geom_fix_object(GEOMETRIC_OBJECT *o);
 extern void geom_fix_objects(void);
 extern void geom_fix_objects0(GEOMETRIC_OBJECT_LIST geometry);
 extern void geom_fix_lattice(void);
@@ -147,10 +147,18 @@ GEOMETRIC_OBJECT make_block(MATERIAL_TYPE material, vector3 center,
 GEOMETRIC_OBJECT make_ellipsoid(MATERIAL_TYPE material, vector3 center,
 				vector3 e1, vector3 e2, vector3 e3,
 				vector3 size);
+
+// prism with `center` field computed automatically from vertices, height, axis
 GEOMETRIC_OBJECT make_prism(MATERIAL_TYPE material,
 			    const vector3 *vertices, int num_vertices,
 			    double height, vector3 axis);
 
+// as make_prism, but with a rigid translation so that the prism is centered at center
+GEOMETRIC_OBJECT make_prism_with_center(MATERIAL_TYPE material, vector3 center,
+                                        const vector3 *vertices, int num_vertices,
+                                        double height, vector3 axis);
+
+
 int vector3_nearly_equal(vector3 v1, vector3 v2, double tolerance);
 
 /**************************************************************************/