RFR: 8236651: Simplify and update glass gtk backend

[Kevin Rushforth]

On Fri, 3 Apr 2020 02:11:12 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> Test on 16.04 (without Webkit - it does not build on 16.04 anymore)
>> 
>> Updated April 2nd.
>> 
>> ![image](https://user-images.githubusercontent.com/30704286/78316727-c14db300-7536-11ea-86e9-4d5c56e4d92c.png)
>> 
>> Note: DatePickerTest works when run alone.
>
> I will keep testing it, but I think it's looking good.

I see a lot of work going into this.

In order for this to progress beyond the prototype or concept phase, we will need to have a discussion on the
openjfx-dev mailing list in a separate email thread that is not directly tied to the PR -- meaning not a reply to the
RFR thread and not a comment in the PR.

@tsayao When you are ready, please send a short email (not a reply to any existing message) to
openjfx-dev at openjdk.java.net with the following:

1. A short summary of the proposed enhancement
2. The goals of the proposed enhancement
3. A description of the proposed changes (basically, the bullet items from the description of this PR)
4. A pointer to this PR for reference

I want to focus the openjfx-dev discussion on getting general agreement on the overall approach rather than on the
details of the code changes. This is a big change, so getting feedback on the overall goals and approach is important;
review comments in the PR aren't the best way to have that discussion.

We aren't following the formal JEP process for JavaFX features, but the JEP template in [JEP
2](https://openjdk.java.net/jeps/2) is a good format to follow for large or high-impact features to make sure that the
motivation, goals, and tradeoffs are documented.

Finally, I note that this will eventually need a CSR, but that can be done once there is agreement on the approach, and
when this is farther along in the review process.

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PR: https://git.openjdk.java.net/jfx/pull/77