X-Git-Url: https://git.jsancho.org/?p=dungeon-master.git;a=blobdiff_plain;f=modules%2Fdungeon-master%2Fgeom.scm;fp=modules%2Fdungeon-master%2Fgeom.scm;h=466d369b5bec16a10761fe74614736857feabac6;hp=0000000000000000000000000000000000000000;hb=8f36ecdca1766ddd2a177fa46dc885c7f8e14130;hpb=4fce641cc077d18f972e250d2fe3be5067618127

diff --git a/modules/dungeon-master/geom.scm b/modules/dungeon-master/geom.scm
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+;;; Dungeon Master --- RPG Adventure Generator
+;;; Copyright © 2019 Javier Sancho <jsf@jsancho.org>
+;;;
+;;; Dungeon Master is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Dungeon Master 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
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Dungeon Master. If not, see <http://www.gnu.org/licenses/>.
+
+
+(define-module (dungeon-master geom)
+  #:use-module (dungeon-master geom point)
+  #:export (angle-sign))
+
+
+(define (angle-sign center a b)
+  "Return the sign of (- (atan (- a center))
+                         (atan (- b center)))"
+  (let ((x1 (- (point-x a) (point-x center)))
+        (y1 (- (point-y a) (point-y center)))
+        (x2 (- (point-x b) (point-x center)))
+        (y2 (- (point-y b) (point-y center))))
+    (cond ((and (>= x1 0) (< x2 0))
+             1)
+          ((and (>= x2 0) (< x1 0))
+             -1)
+          ((and (= x1 0) (= x2 0))
+           (if (> y2 y1) 1 -1))
+          (else
+           (if (> (- (* x2 y1) (* x1 y2)) 0) 1 -1)))))