#|is-empty? fails when called on a region produced without an associated
dc...|#
(define intersection
(lambda (region-a region-b)
(define new-region (new region%))
(send new-region union region-a)
(send new-region intersect region-b)
new-region))
#|-Patrick|#
On 2 May 2012 17:55, Patrick Mahoney <paddy.maho...@gmail.com> wrote:
> #|Hello All,
> I'm attempting to ensure that shapes drawn onto a canvas don't overlap. In
> order to do so, I attempted to use region% objects.| #
>
> #|Takes two rectangles, and tells whether they overlap as regions.|#
> (define overlaps?
> (lambda (rect-a rect-b)
> (define region-a (rectangle->region rect-a))
> (define region-b (rectangle->region rect-b))
> (define a-intersection-b (intersection dc region-a region-b))
> (send a-intersection-b is-empty?)))
>
> #|Unfortunately this doesn't work-the is-empty? method only works on a
> region% with an associated drawing context. Is there any way to salvage
> this such that is-empty? can be used on region% objects unassociated with a
> dc object? I'm not sure why they would require one, as otherwise the
> region% interface seems fairly decoupled from the notion of
> device-contexts. However, I'm sure that there is a reason that I don't yet
> understand.|#
>
> (define intersection
> (lambda (region-a region-b)
> (define new-region (new region% [dc a-dc]))
> (send new-region union region-a)
> (send new-region intersect region-b)
> new-region))
>
> #|The region documentation...
> http://docs.racket-lang.org/draw/region_.html?q=region&q=any-of%3F#%28meth._%28%28%28lib._racket/draw..rkt%29._region~25%29._in-region~3f%29%29<http://docs.racket-lang.org/draw/region_.html?q=region&q=any-of%3F#%28meth._%28%28%28lib._racket/draw..rkt%29._region%7E25%29._in-region%7E3f%29%29>
>
> I really just don't want to have to rewrite the overlaps? logic for my set
> of shapes. Thanks all. |#
>
>
>
____________________
Racket Users list:
http://lists.racket-lang.org/users
