From: David Kastrup <dak@gnu.org>
Date: Fri, 9 Oct 2015 14:17:49 +0000 (+0200)
Subject: Issue 4634: Simplify coord-rotate
X-Git-Tag: release/2.19.29-1~5
X-Git-Url: https://git.donarmstrong.com/?a=commitdiff_plain;h=e860e146ccecf07d42aa53de885916931950245e;p=lilypond.git

Issue 4634: Simplify coord-rotate

This does not fix the problem that (sin PI) is not really zero because
of the MPU working with higher precision than PI is specified, but at
least it makes the code nicer to read and modify.
---

diff --git a/scm/lily-library.scm b/scm/lily-library.scm
index c5bf8cc59d..0bfce9eb0c 100644
--- a/scm/lily-library.scm
+++ b/scm/lily-library.scm
@@ -707,20 +707,13 @@ right (@var{dir}=+1)."
 (define-public (coord-scale coordinate amount)
   (coord-operation * amount coordinate))
 
-(define-public (coord-rotate coordinate degrees-in-radians)
-  (let*
-      ((coordinate
-        (cons
-         (exact->inexact (coord-x coordinate))
-         (exact->inexact (coord-y coordinate))))
-       (radius
-        (sqrt
-         (+ (* (coord-x coordinate) (coord-x coordinate))
-            (* (coord-y coordinate) (coord-y coordinate)))))
-       (angle (angle-0-2pi (atan (coord-y coordinate) (coord-x coordinate)))))
-    (cons
-     (* radius (cos (+ angle degrees-in-radians)))
-     (* radius (sin (+ angle degrees-in-radians))))))
+(define-public (coord-rotate coordinate angle)
+  (let ((c (cos angle))
+        (s (sin angle))
+        (x (coord-x coordinate))
+        (y (coord-y coordinate)))
+    (cons (- (* c x) (* s y))
+          (+ (* s x) (* c y)))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; trig