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racket/gui: fix auto-scrollbars for editor GUI

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It's possible to go from a state where one scroll bar is needed
(vertical or horizontal) to a state where each scrollbar is
needed iff the other scrollbar is needed. In that case, the
auto-scrollbar algorithm couldn't find either fixpoint and
would loop forever.
This commit is contained in:
Matthew Flatt 2013-03-21 14:58:10 -06:00
parent 87facb736f
commit b041a151e6
1 changed files with 19 additions and 3 deletions
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22
collects/mred/private/wxme/editor-canvas.rkt
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@ -752,7 +752,7 @@
(begin
(set! given-h-scrolls-per-page -2)
#f)
(let loop ([retval #f])
(let loop ([retval #f] [iters 0])
(let-boxes ([sx 0]
[sy 0])
(get-scroll sx sy)
@ -806,7 +806,7 @@
(set! scroll-offset -scroll-offset)
(let-values ([(num-scrolls vspp)
(let-values ([(vnum-scrolls vspp)
(if (positive? vnum-scrolls)
(let ([num-lines (- (send med num-scroll-lines) 1)])
(values vnum-scrolls
@ -908,8 +908,24 @@
(set! scroll-width hnum-scrolls)
(set! scroll-height vnum-scrolls)
(when (and go-again? (iters . > . 2))
;; we're not reaching a fixpoint, so
;; it seems that a horizontal scroll
;; is needed iff there's a vertical
;; scrollbar; force a fixpoint
(cond
[(and auto-x? auto-y?)
(set! xscroll-on? #f)
(set! yscroll-on? #f)]
;; I don't think these cases are possible,
;; but in case I have it wrong, conservatively
;; force scrollbars on.
[auto-x? (set! xscroll-on? #t)]
[auto-y? (set! yscroll-on? #t)])
(show-scrollbars xscroll-on? yscroll-on?))
(if go-again?
(loop #t)
(loop #t (add1 iters))
#t))))))
retval)))))))