Hi all, I needed a GUI container that allows the contained components to choose where they are placed in the container. i.e. A container that doesn't try to stretch and re-'place' its containees, instead letting the containees figure out where they want to be. I was surprised that this particular container/containee use-case wasn't readily available in Racket (since it is 'the' fundamental layout elsewhere), so I implemented a version and post it here in case it is useful to others. (If I'm going about it wrong, then please do let me know.) Cheers, Kieron. p.s. I notice the canvas border is actually painted only on the top and left (see capture-self-placeable). Should the border also be painted on the bottom and right? **** #lang racket/gui ; Specify in an interface the methods that a containee needs to make it self-placeable. (define self-placeable-containee<%> (interface () get-preferred-x get-preferred-y get-preferred-x-y set-preferred-x set-preferred-y set-preferred-x-y)) ; Define in a mixin the default implementations for a self-placeable containee. (define (self-placeable-containee%% %) (class* % (self-placeable-containee<%>) (super-new) (define preferred-x 0) (define preferred-y 0) (define/public (get-preferred-x) preferred-x) (define/public (get-preferred-y) preferred-y) (define/public (get-preferred-x-y) (values preferred-x preferred-y)) (define/public (set-preferred-x x) (set! preferred-x x)) (define/public (set-preferred-y y) (set! preferred-y y)) (define/public (set-preferred-x-y x y) (set! preferred-x x) (set! preferred-y y)) )) ; Define a custom container panel that can place the self-placeable containees. (define placer-panel% (class panel% (inherit get-children min-width min-height) (super-new) ; container-size is called with each child's dimensions and strechability, ; and returns the container's required minimum dimensions. ; In this case, the containee size's are ignored, ; and the container's (previously set) minimum width and height are returned. [define/override (container-size containee-sizes) ; (printf "container-size:~a\n" containee-sizes) (values (min-width) (min-height))] ; place-children is called with each child's dimensions and strechability, ; and returns each child's location and dimensions. ; In this case, each containee is simply asked where it wants to be (previously set). ; No adustments are made to a containee's size so as to use any empty space in the container. ; i.e. A containee's strechability is ignored, and each containee remains the (previously set) minimum width and height. [define/override (place-children containee-sizes container-width container-height) ; (printf "place-children:~a\n" containee-sizes) (map (lambda (containee-size containee) (let*-values ([(min-width min-height h-stretch? v-stretch?) (apply values containee-size)] [(x y) (send containee get-preferred-x-y)] ) (list x y min-width min-height))) containee-sizes (get-children))] )) (define self-placeable-canvas% (class (self-placeable-containee%% canvas%) (inherit set-preferred-x-y) (init x y) (super-new) (set-preferred-x-y x y) )) (define frame-1 (new frame% [label "Self Placeable Containees"] [x 30] [y 30] [min-width 800] [min-height 600])) (define panel-1 (new placer-panel% [parent frame-1] )) (define canvas-1 (new self-placeable-canvas% [parent panel-1] [style (list 'border)] [x 25] [y 25] [min-width 500] [min-height 75])) (define canvas-2 (new self-placeable-canvas% [parent panel-1] [style (list 'border)] [x 275] [y 275] [min-width 100] [min-height 100])) (define canvas-3 (new self-placeable-canvas% [parent panel-1] [style (list 'border)] [x 600] [y 125] [min-width 100] [min-height 400])) (send frame-1 show #t)