Modules reorganization

[dungeon-master.git] / modules / dungeon-master / geom / triangle.scm

diff --git a/modules/dungeon-master/geom/triangle.scm b/modules/dungeon-master/geom/triangle.scm
new file mode 100644 (file)
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+++ b/modules/dungeon-master/geom/triangle.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 triangle)
+  #:use-module (ice-9 receive)
+  #:use-module (srfi srfi-9)
+  #:use-module (dungeon-master geom point)
+  #:export (make-triangle
+            triangle?
+            triangle-points
+            triangle-center
+            triangle-radius
+            triangle-has-edge))
+
+(define-record-type <triangle>
+  (make-raw-triangle points center radius)
+  triangle?
+  (points triangle-points)
+  (center triangle-center)
+  (radius triangle-radius))
+
+(define (make-triangle p1 p2 p3)
+  (let ((center (circumcenter p1 p2 p3)))
+    (make-raw-triangle
+     (list p1 p2 p3)
+     center
+     (points-distance center p1))))
+
+(define (circumcenter p1 p2 p3)
+  (receive (a b c)
+      (perpendicular-line-from-points p1 p2)
+    (receive (e f g)
+        (perpendicular-line-from-points p2 p3)
+      (let ((determinant (- (* a f) (* e b))))
+        (make-point
+         (/ (- (* f c) (* b g)) determinant)
+         (/ (- (* a g) (* e c)) determinant))))))
+
+(define (perpendicular-line-from-points p1 p2)
+  (let ((x1 (point-x p1))
+        (y1 (point-y p1))
+        (x2 (point-x p2))
+        (y2 (point-y p2)))
+    (let* ((a (- y2 y1))
+           (b (- x1 x2))
+           (c (+ (* a x1) (* b y2))))
+      (let ((mid-x (/ (+ x1 x2) 2))
+            (mid-y (/ (+ y1 y2) 2)))
+        (values (- b)
+                a
+                (+ (* (- b) mid-x) (* a mid-y)))))))
+
+(define (triangle-has-edge triangle a b)
+  (let ((points (triangle-points triangle)))
+    (let ((p1 (car points))
+          (p2 (cadr points))
+          (p3 (caddr points)))
+      (or (and (equal? p1 a) (equal? p2 b))
+          (and (equal? p1 b) (equal? p2 a))
+          (and (equal? p2 a) (equal? p3 b))
+          (and (equal? p2 b) (equal? p3 a))
+          (and (equal? p3 a) (equal? p1 b))
+          (and (equal? p3 b) (equal? p1 a))))))