RFR: 8330559: Trailing space not rendering correctly in TextFlow in RTL mode

[John Hendrikx]

On Tue, 4 Jun 2024 05:32:23 GMT, Karthik P K <kpk at openjdk.org> wrote:

>> I think if this is specific to mac, and doesn't occur on other platforms that the supplied `positions` may be incorrect by the underlying `*GlyphLayout` code.  Under Windows it will likely use the `DWGlyphLayout` to supply `positions`.  On Mac this will be `CTGlyphLayout`.
>> 
>> The more prudent course of action than seems to be to fix what is supplied by `CTGlyphLayout` instead of working around it in `TextRun`.
>> 
>> I haven't checked it that extensively yet, but I think `positions` is not supposed to contain negative `x` values at all when not in compact mode.
>
> Yes the issue is specific to Mac only. Windows uses `DWGlyphLayout` for positions as you pointed out.
> Since the position obtained from the underlying platform itself is not correct Mac, looked like fixing it in either `TextRun`  or in the native side does not make huge difference so went with this approach. However I will explore how we can fix it on the native side.
> 
> If the `positions` is not supposed to contain negative value, it is an issue from Apple not in JavaFX. In this case should we actually fix the issue in JavaFX, as it becomes a workaround rather than a fix regardless of where we fix it.

The `*GlyphLayout` classes are adapters for a platform.  Their job is to call native code, and to convert it to a standard format that JavaFX expects.  The native code for Apple is probably perfectly fine, but it is not adapted to the standard format correctly for the case that you discovered.  I'm suggesting therefore to change the `CTGlyphLayout` class to adapt/modify the `positions` array before it is given to JavaFX code that expects it to be in a specific format.

`CTGlyphLayout` calls:

            run.shape(glyphCount, glyphs, positions, indices);

It should not be too hard to fix `positions` passed here to be in the correct format so `TextRun` can remain unchanged.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1468#discussion_r1625493122