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

[John Hendrikx]

On Fri, 31 May 2024 16:54:58 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> The issue is specific to Mac. The glyph positions returned from native side for complex text is not handled in the text render logic. This issue is observed only when trailing spaces are present along with LTR text mixed with RTL text (Example: "Arabic: العربية").
>> 
>> Made changes in `getPosX` of `TextRun` class to handle negative values.
>> 
>> Tested the changes manually with the sample code present in the bug and using the MonkeyTester.
>
> 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.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1468#discussion_r1623146989