RFR: 8354191: GTK LaF should use pre-multiplied alpha same as cairo

[Sergey Bylokhov]

On Fri, 11 Apr 2025 06:01:32 GMT, Maxim Kartashev <mkartashev at openjdk.org> wrote:

>> src/java.desktop/share/classes/com/sun/java/swing/plaf/gtk/GTKEngine.java line 618:
>> 
>>> 616:             int index = transparency - 1;
>>> 617:             if (COLOR_MODELS[index] == null) {
>>> 618:                 COLOR_MODELS[index] = GraphicsEnvironment.getLocalGraphicsEnvironment()
>> 
>> How will it work if the configuration changes at runtime?
>
> There will be an additional pixel conversion effort from the outdated configuration's format to the new actual format when this image is used. In other words, status quo.

@mkartashev Did you check that the scenario described above cannot happen?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24551#discussion_r2049418916