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

[Karthik P K]

On Sat, 1 Jun 2024 04:53:48 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> modules/javafx.graphics/src/main/java/com/sun/javafx/text/TextRun.java line 332:
>> 
>>> 330:                 return x;
>>> 331:             }
>>> 332:             int prevIdx = (glyphIndex - 1)<<1;
>> 
>> would it be possible to add a comment explaining why this code is doing what it's doing?  specifically, the reason for the while() loop and Math.abs().  and perhaps mention that this happens on mac only.
>
> 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.

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1468#discussion_r1625369735