RFR: 8341670: [Text, TextFlow] Public API for Text Layout Info [v3]

[Phil Race]

On Wed, 9 Oct 2024 20:58:21 GMT, Phil Race <prr at openjdk.org> wrote:

>> thank you!
>> 
>> I am struggling with how to explain that it should neither be cached, nor compared to another snapshot.
>> 
>> Maybe an example would help.  Use case is an editable rich text component based on `TextFlow`.  The user presses `HOME` and the caret needs to go to the beginning of the line.  We get the `LayoutInfo`, determine which line the caret is currently at and determine the start offset of that line to move the caret to.
>> 
>> Another example: in `Text`, to determine whether the mouse is clicked inside of the text or beyond the last character (see [JDK-8091012](https://bugs.openjdk.org/browse/JDK-8091012) ).
>> 
>> We are not expecting the application to monitor the text layout, so no notifications or observable properties or equals() are needed.
>> 
>> (I've added some words to that effect in `Text/TextFlow.getLayoutInfo()` )
>
> Clients will usually obtain a LayoutInfo in order to respond to some user action or an update of the target node.
> LayoutInfo should be considered an ephemeral snapshot, to be used and immediately discarded.
> Clients should always obtain a new one when they need to respond again as likely the trigger to respond again means the target node has changed.

Although I don't see the harm in being more efficient.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1596#discussion_r1794216880