X-Git-Url: https://git.jsancho.org/?p=dungeon-master.git;a=blobdiff_plain;f=dungeon-master%2Fgeom%2Ftriangle.scm;fp=dungeon-master%2Fgeom%2Ftriangle.scm;h=123dd0568e57910caa3237e4f5563cac2059f370;hp=0000000000000000000000000000000000000000;hb=695ecf94f5bb10ced4e66b0b4d036de9965c02ca;hpb=4e1254800a1c453aba76b8ccd5b632f38a71aed7

diff --git a/dungeon-master/geom/triangle.scm b/dungeon-master/geom/triangle.scm
new file mode 100644
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--- /dev/null
+++ b/dungeon-master/geom/triangle.scm
@@ -0,0 +1,60 @@
+(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))))))