RFR: 8314482: TextFlow: TabStopPolicy [v3]

[Andy Goryachev]

On Wed, 18 Jun 2025 15:34:15 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> # Tab Stop Policy
>> 
>> Andy Goryachev
>> 
>> <andy.goryachev at oracle.com>
>> 
>> 
>> ## Summary
>> 
>> Introduce a `tabStopPolicy` property in the `TextFlow` class which, when set, overrides the existing `tabSize`
>> value and provides consistent way of setting tab stops at the paragraph level, regardless of the individual text
>> segments font [0].
>> 
>> ![Screenshot 2025-05-19 at 15 03 26](https://github.com/user-attachments/assets/32f2474d-7d2b-47b0-a22c-410d485f4e40)
>> 
>> 
>> ## Goals
>> 
>> The goal of this proposal is to provide a better way for controlling tab stops in the `TextFlow` containing rich text.
>> 
>> 
>> 
>> ## Non-Goals
>> 
>> The following are not the goals of this proposal:
>> 
>> - support for tab stop types (BAR, or DECIMAL), or attributes like `alignment`
>> - support the `leader` property (symbols to fill the empty space before the tab stop)
>> - support for `firstLineIndent` property
>> - deprecate the `TextFlow::tabsize` property
>> 
>> 
>> 
>> ## Motivation
>> 
>> The existing `tabSize` property in the `TextFlow` is inadequate for representing tab stops when the content
>> contains text with different font sizes.
>> 
>> In addition to that, a rich text editor might require support for user-customizable tab stops, similar to that provided
>> in RTF or MS Word documents.
>> 
>> 
>> 
>> 
>> ## Description
>> 
>> ### TextFlow
>> 
>> 
>>     /**
>>      * {@code TabAdvancePolicy} determines the tab stop positions within this {@code TextFlow}.
>>      * <p>
>>      * A non-null {@code TabAdvancePolicy} overrides values set by {@link #setTabSize(int)},
>>      * as well as any values set by {@link Text#setTabSize(int)} in individual {@code Text} instances within
>>      * this {@code TextFlow}.
>>      *
>>      * @defaultValue null
>>      *
>>      * @since 999 TODO
>>      */
>>     public final ObjectProperty<TabStopPolicy> tabStopPolicyProperty() {
>> 
>>     public final TabStopPolicy getTabStopPolicy() {
>> 
>>     public final void setTabStopPolicy(TabStopPolicy policy) {
>> 
>>     /**
>>      * The size of a tab stop in spaces.
>>      * Values less than 1 are treated as 1. This value overrides the
>>      * {@code tabSize} of contained {@link Text} nodes.
>>      * <p>
>> +     * Note that this method should not be used to control the tab placement when multiple {@code Text} nodes
>> +     * with different fonts are contained within this {@code TextFlow}.
>> +     * In this case, the {@link #setTabStopPolicy(TabStopPolicy)} should be used instead.
>>      *
>>      * @defaultValue 8
>>      *...
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comments

> question: what about setting the tab stop policy via CSS?

A very good question!

It might be entirely possible (in a separate PR), though judging by experience from adding tab stops to the rich editor demo https://github.com/openjdk/jfx/pull/1800 it's probably unnecessary, since TextFlow is somewhat of a low-level control.

Another complication is that the policy is a complex entity, with a list of (possibly complex) `TabStop`s, and other fields, so I am not sure how easy it would be to add CSS support.  How would it look in CSS?

Also, decided to make the `TabStop` class `final`.  We can always remove the `final` keyword if the use case arises.

-------------

PR Comment: https://git.openjdk.org/jfx/pull/1744#issuecomment-2985361243
PR Comment: https://git.openjdk.org/jfx/pull/1744#issuecomment-2985364601