Find the intersection of two lines: Difference between revisions

=={{header|Emacs Lisp}}==

<syntaxhighlight lang="lisp">

;; y = a*x + b

(let ()

(defun line-prop (p1 p2)

(let* ((prop-a (/ (- (plist-get p2 'y) (plist-get p1 'y))

(- (plist-get p2 'x) (plist-get p1 'x))))

(prop-b (- (plist-get p1 'y) (* prop-a (plist-get p1 'x)))))

(list 'a prop-a 'b prop-b) ) )

(defun calculate-intersection (line1 line2)

(let (int-x int-y)

(setq int-x (/ (- (plist-get line2 'b) (plist-get line1 'b))

(- (plist-get line1 'a) (plist-get line2 'a))))

(setq int-y (+ (* (plist-get line1 'a) int-x) (plist-get line1 'b)))

(list 'x int-x 'y int-y) ) )

(let ((p1 '(x 4.0 y 0.0)) (p2 '(x 6.0 y 10.0))

(p3 '(x 0.0 y 3.0)) (p4 '(x 10.0 y 7.0)))

(let ((line1 (line-prop p1 p2))

(line2 (line-prop p3 p4)))

(message "%s" (calculate-intersection line1 line2) ) ) )

</syntaxhighlight>

{{out}}

<pre>

(x 5.0 y 5.0)

</pre>