From e362e357faf60f8258ac813f917e08ffd76d5668 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sun, 24 Apr 2016 21:30:06 -0400
Subject: math: vector: Add polar2 procedure.

* sly/math/vector.scm (polar2): New procedure.
* doc/api/math.texi (Vectors): Document it.
---
 doc/api/math.texi   | 5 +++++
 sly/math/vector.scm | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/doc/api/math.texi b/doc/api/math.texi
index 9582ea7..61aa17f 100644
--- a/doc/api/math.texi
+++ b/doc/api/math.texi
@@ -60,6 +60,11 @@ Create a new 4D vector with coordinates (@var{x}, @var{y}, @var{z},
 @var{w}).
 @end deffn
 
+@deffn {Scheme Procedure} polar2 @var{r} @var{theta}
+Create a new 2D vector from the polar coordinate (@var{r},
+@var{theta}) where @var{r} is the radius and @var{theta} is the angle.
+@end deffn
+
 @deffn {Scheme Syntax} vector2? @var{v}
 Return @code{#t} if @code{v} is a 2D vector.
 @end deffn
diff --git a/sly/math/vector.scm b/sly/math/vector.scm
index bd556ea..cc03e4e 100644
--- a/sly/math/vector.scm
+++ b/sly/math/vector.scm
@@ -31,6 +31,7 @@
             <vector4>
             vector2 vector3 vector4
             vector2? vector3? vector4?
+            polar2
             vx vy vz vw
             vmap v+ v- v* vdot vcross
             magnitude normalize vlerp)
@@ -79,6 +80,12 @@
 
 (define vw vector4-w)
 
+(define (polar2 r theta)
+  "Create a new 2D vector from the polar coordinate (R, THETA) where R
+is the radius and THETA is the angle."
+  (vector2 (* r (cos theta))
+           (* r (sin theta))))
+
 (define (vmap proc v)
   "Return a new vector that is the result of applying PROC to each
 element of the 2D/3D/4D vector V."
-- 
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