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;;; guile-2d
;;; Copyright (C) 2013 David Thompson <dthompson2@worcester.edu>
;;;
;;; Guile-2d is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; Guile-2d is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Vector math operations.
;;
;;; Code:
(define-module (2d vector)
#:use-module (rnrs base)
#:export (vx
vy
vz
v+
v*
scale
mag
normalize
vector-reduce
vector-from-polar))
(define (vx vector)
"Returns the first element of a vector."
(vector-ref vector 0))
(define (vy vector)
"Returns the second element of a vector."
(vector-ref vector 1))
(define (vz vector)
"Returns the third element of a vector."
(vector-ref vector 2))
(define (v+ . vectors)
"Adds vectors."
(apply vector-map + vectors))
(define (v* . vectors)
"Multiplies vectors."
(apply vector-map * vectors))
(define (scale vector scalar)
"Multiplies a vector by a scalar."
(vector-map (lambda (e) (* scalar e)) vector))
(define (mag vector)
"Returns the magnitude of a vector."
(sqrt (vector-reduce + 0 (vector-map (lambda (e) (* e e)) vector))))
(define (normalize vector)
"Normalizes a vector."
(let ((m (mag vector)))
(vector-map (lambda (e) (/ e m)) vector)))
(define (vector-reduce proc default vector)
"Performs a reduce operation on a vector."
(cond ((= (vector-length vector) 0)
default)
((= (vector-length vector) 1)
(vector-ref vector 0))
(else
(let loop ((i 2)
(prev (proc (vector-ref vector 0)
(vector-ref vector 1))))
(if (= (vector-length vector) i)
prev
(loop (1+ i) (proc prev (vector-ref vector i))))))))
(define (vector-from-polar r theta)
"Converts polar coordinates into a cartesian vector."
(vector (* r (cos theta))
(* r (sin theta))))
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