RFR: 8225571: Port DND source to use GTK instead of GDK

[Kevin Rushforth]

On Tue, 10 Dec 2019 19:41:05 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> I'm starting to look at this. I see at least one behavioral difference that will need to be addressed. With the existing implementation, if I drag / drop onto a target that set up to receive the drop, the transfer completes with a transfer mode of `null`. With your patch, the transfer never completes -- the `DRAG_DONE` event is never sent.
>> 
>> This can be most easily seen by running the `DragDropWithControls` app and doing one of the following two things:
>> 
>> 1.  Drag from the source rectangle and drop somewhere _other than_ the target rectangle, for example, in the status text box at the bottom.
>> 2. Change the source data format to `HTML` (uncheck `PLAINTEXT`), leaving the target at `PLAINTEXT`, then drag from the source rectangle and drop onto the target rectangle
>> 
>> In addition to the drop not happening, I get the following assertion error on Ubuntu 16.04:
>> 
>> (java:22328): Gdk-CRITICAL **: gdk_frame_clock_get_frame_time: assertion 'GDK_IS_FRAME_CLOCK (frame_clock)' failed
>> 
>> I'm using the default GTK 3 library.
> 
> @kevinrushforth I changed that behaviour. Since the drag does not complete i find it counter-intuitive to send the DRAG_DONE event.
> 
> Does it send the event on other platforms? I can test on Windows.
> 
> Will look into the assertion error - it does not happen on 18.04.

> Does it send the event on other platforms? I can test on Windows.

Yes, it always sends the `DRAG_DONE` event on all platforms today (I tested it on Mac, Windows, and Linux).

> Will look into the assertion error - it does not happen on 18.04.

It doesn't happen on 19.10 either. Only 16.04 as far as I have tested. I'll also test on Oracle Linux 7.x.

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PR: https://git.openjdk.java.net/jfx/pull/4