+ (values (- minx (/ dx 2))
+ (- miny (/ dy 2))
+ (+ maxx (/ dx 2))
+ (+ maxy (/ dy 2)))))))
+
+(define (calculate-mesh points triangles vertices)
+ (cond ((null? vertices)
+ (values points triangles))
+ (else
+ (let ((vertice (car vertices)))
+ (receive (to-split to-keep)
+ (triangles-contains-point triangles vertice)
+ (cond ((null? to-split)
+ (calculate-mesh points triangles (cdr vertices)))
+ (else
+ (calculate-mesh (cons vertice points)
+ (concatenate (calculate-new-triangles to-split vertice)
+ to-keep)
+ (cdr vertices)))))))))
+
+(define (calculate-new-triangles to-split p1)
+ (let ((vertices (calculate-new-vertices to-split)))
+ (let* ((a (car vertices))
+ (b (cadr vertices))
+ (len (length a)))
+ (let loop ((sublist-a a)
+ (triangles '()))
+ (cond (sublist-a
+ (let ((p2 (car sublist-a))
+ (p3 (list-ref b (- len (length sublist-a)))))
+ (loop (member p3 a)
+ (cons (make-triangle p1 p2 p3) triangles))))
+ (else
+ triangles))))))
+
+(define* (calculate-new-vertices triangles #:optional (original-t triangles) (a '()) (b '()))
+ (cond ((null? triangles)
+ (list a b))
+ (else
+ (let* ((triangle (car triangles))
+ (common-edge (triangles-has-common-edge triangle original-t)))
+ (let ((points (triangle-points triangle)))
+ (let ((p1 (car points))
+ (p2 (cadr points))
+ (p3 (caddr points))
+ (e1 (car common-edge))
+ (e2 (cadr common-edge))
+ (e3 (caddr common-edge)))
+ (cond (e1
+ (set! a (cons p1 a))
+ (set! b (cons p2 b))))
+ (cond (e2
+ (set! a (cons p2 a))
+ (set! b (cons p3 b))))
+ (cond (e3
+ (set! a (cons p3 a))
+ (set! b (cons p1 b))))
+ (calculate-new-vertices (cdr triangles) original-t a b)))))))
+
+(define* (triangles-has-common-edge triangle triangles #:optional (e1 #t) (e2 #t) (e3 #t))
+ (cond ((not (or e1 e2 e3))
+ (list e1 e2 e3))
+ ((null? triangles)
+ (list e1 e2 e3))
+ (else
+ (let ((t (car triangles)))
+ (cond ((equal? t triangle)
+ (triangles-has-common-edge triangle (cdr triangles) e1 e2 e3))
+ (else
+ (let ((points (triangle-points triangle)))
+ (let ((p1 (car points))
+ (p2 (cadr points))
+ (p3 (caddr points)))
+ (when (and e1 (triangle-has-edge t p2 p1))
+ (set! e1 #f))
+ (when (and e2 (triangle-has-edge t p3 p2))
+ (set! e2 #f))
+ (when (and e3 (triangle-has-edge t p1 p3))
+ (set! e3 #f))))
+ (triangles-has-common-edge triangle (cdr triangles) e1 e2 e3)))))))
+
+(define (triangles-contains-point triangles point)
+ (partition
+ (lambda (triangle)
+ (< (points-distance point (triangle-center triangle))
+ (triangle-radius triangle)))
+ triangles))