[Tcl-bugs] [Tk] (marc_culler) tkt (Open): XGetImage fails on Mac using Tk 9.0.b3

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Ticket Change [84a571f32e7667da14d101ae02999ec94c4071dc4f8f218832732a297c9b514f]
  [XGetImage fails on Mac using Tk 9.0.b3]
  By      marc_culler
  For     Tk
  On      2024-08-09T17:01:58.268
  Details https://core.tcl-lang.org/tk/tinfo?name=84a571f32e7667da14d101ae02999ec94c4071dc4f8f218832732a297c9b514f
  Ticket  https://core.tcl-lang.org/tk/tktview/b7d813f008173e9760fe13a07749dc3f513faf41

Changed Fields
  comment:  The Img extension uses XGetImage for format option "-window" to get a
            "screenshot" of a widget.  This fails using Tk 9.0.b3 on ac. Previous
            versions (8.6, 8.7, 9.0.b2) worked fine.  It also works fine using
            Tk9.0.b3 on Windows or Linux.

            The call of XGetImage returns NULL, because the CGImageRef returned by
            function   CreateCGImageFromDOrawableRect only has 3 samples per
            pixel, but is checked for having 4.  This new behaviour seems to be
            related to changes at the beginning of function
            CreateCGImageFromDrawableRect, where a CGContextRef is created.

            Attached test script derived from the Img test suite demonstrates the
            error.
  icomment: I am not sure whether the Img extension is expecting that XGetImage
            would  somehow be expected to know what the entire Canvas scrollregion
            looks like,  even though parts of it had never been drawn to the
            scteen. With the old  implementation which would create a new CGImage
            and ask the canvas to  redraw itself using a graphics context for that
            CGImage, it would be easier  to imagine how to create an image of the
            entire Canvas. But I don't know  how XGetImage would even be able to
            find the dimensions of the scrollregion,  since I don't think it is
            supposed to have any knowledge of the inner  workings of the window it
            is getting an image from.

            I think I am pretty far from understanding how the Img extension
            implements  the -format window -data $canv options that you are using
            in your script.  I will need an explanation.
  login:    marc_culler
  username: Marc Culler

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