RFR: 8301302: Platform preferences API [v3]

[John Hendrikx]

On Mon, 24 Apr 2023 06:23:41 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> > I'm not convinced that a delayed change + commit system is the correct way to do this. Properties should behave the same everywhere in JavaFX and this seems to change how they work quite a bit.
> > Instead, I propose to look at how layout in JavaFX is handling this problem. Layout looks at thousands of properties, yet changing one or many of the involved properties does not involve an expensive layout recalculation per change. Instead, changes are tracked by marking certain aspects of the involved controls dirty. On the next pulse, the layout code notices that something that would influence layout and CSS decisions has changed, and performs the required changes. The properties involved are all normal properties, that can be changed quickly, reflect their current value immediately and that can be overridden by the user or reset back to defaults. There is no override or commit system needed.
> > Have you considered allowing users to change preference values directly, but not acting on those changes until the next pulse occurs? Users can still listen for keys/properties, just like they can for layout properties, but the major changes that involve recomputing CSS is only done once per pulse.
> > This would make it possible to change several preference values without penalty (which happens on the FX thread anyway, so pulses are on hold during that time), and they're automatically "committed" once the user is done on the FX thread and the next pulse fires. I think it would be a very good fit.
> 
> I think this could work, but it also means giving up on instant change notifications. A call to `setAppearance` or `override(key, value)` will not instantly fire a change notification (after the code that modifies the properties is done), but delay it until the next pulse. Resetting the value to its original value before the next pulse would probably also elide the change notification entirely. It's basically the same as change+commit, but with an implicit commit in the next pulse.

That's not quite what I meant. You can add listeners still and get instant change notifications.  Just like when I listen to the `backgroundProperty` of a control, and someone changes it, I get notified instantly and the change is reflected (in the property) instantly.  Only when the next pulse fires is the change actually rendered.

I would think the same is possible with say the appearance property.  When I change it from LIGHT to DARK, everyone interested gets this notification immediately.  On the next pulse, the change is noticed and only then do we change the stylesheets or make other adjustments that are high impact.  Basically, the computationally expensive stuff happens during a pulse; it could register invalidation listeners on properties of interest which just set a flag, that is checked and reset on the next pulse.

I'm not 100% sure, but it seems you want to add listeners to these properties yourself to instantly trigger the Theme updating code -- I'm saying, only set a boolean that they've changed, check it on the next pulse using `Scene#addPreLayoutPulseListener` (or perhaps there is another mechanism you can tap into internally), and then trigger the Theme change.

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PR Comment: https://git.openjdk.org/jfx/pull/1014#issuecomment-1519514059