[racket] Can I make the frame% instances transparent?

Thanks.
This saved lots of time.


On Mon, Jan 20, 2014 at 10:39 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:

> The `frame%` class does not offer a transparency option, but on Mac OS
> X, you can use the FFI to make a frame transparent at the Cocoa
> NSWindow layer.
>
> Here's an example:
>
> --------------------------------------------------
>
> #lang racket/gui
> (require ffi/unsafe
>          ffi/unsafe/objc)
>
> ;; Create the frame:
> (define f (new frame%
>                [label "Example"]
>                [width 200]
>                [height 200]))
>
> ;; Add a transparent canvas that displays "Hello"
> (new canvas%
>      [parent f]
>      [style '(transparent)]
>      [paint-callback (lambda (c dc)
>                        (send dc draw-text "Hello" 0 0))])
>
> ;; The `CGFloat` type depends on the platform:
> (define 64-bit? (= (ctype-sizeof _long) 8))
> (define _CGFloat (if 64-bit? _double _float))
>
> ;; Get an `NSWindow` from the `frame%` object:
> (define h (send f get-handle))
>
> ;; Set the background's transparency at the `NSWindow` level:
> (import-class NSColor)
> (tellv h setBackgroundColor: (tell NSColor
>                                    colorWithRed: #:type _CGFloat 1.0
>                                    green: #:type _CGFloat 1.0
>                                    blue: #:type _CGFloat 1.0
>                                    alpha: #:type _CGFloat 0.5))
> (tellv h setOpaque: #:type _BOOL NO)
>
> ;; Show the frame:
> (send f show #t)
>
>
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