On Thu, 6 Jun 2024 23:47:44 GMT, Andy Goryachev <ango...@openjdk.org> wrote:
>> I'm having some doubts about the solution still. It is mentioned that this
>> problem can occur in text containing both LTR and RTL text together,
>> however, as far as I can see, a `TextRun` never contains a mix of text
>> directions. Can you clarify this?
>>
>> Also in RTL text, I'm guessing "trailing" spaces are in fact what we call
>> leading spaces in LTR text, ie. trailing spaces in a RTL text sample would
>> be: ` قطة`
>>
>> I'm guessing that CT (Core Text) returns the positions of all the trailing
>> spaces as negative values, not just the first, and the first glyph (seen
>> from the left) with an offset of 0. Since the CT framework can also handle
>> alignments, but FX is not making use of this, I think all calculations are
>> done with the standard left alignment. It would make sense for spaces that
>> "fall off" the left end (because they're "trailing") to have negative
>> values. Similarly, if you did LTR text for `cat ` with a right alignment,
>> all glyphs would have negative values, except the two trailing spaces that
>> would have positive values.
>>
>> So I'm curious to see what happens if you have more than one trailing space
>> (eg. ` قطة`) and what `CTRunGetPositions` returns then.
>
> Yes, I am also curious about the exact meaning of these negative values.
> I'm having some doubts about the solution still. It is mentioned that this
> problem can occur in text containing both LTR and RTL text together, however,
> as far as I can see, a `TextRun` never contains a mix of text directions. Can
> you clarify this?
>
LTR and RTL text will not be together in a TextRun but negative value will not
be obtained for spaces in all the cases.
For example: In the the case where Text nodes are present in TextFlow like
shown below, none of the spaces will have negative value. In fact
`CTGlyphLayout` class will not be called at all.
flow = new TextFlow(
t("Arabic", Color.RED),
t(" ", Color.YELLOW),
t("Arabic", Color.RED));
If we consider cases like
flow = new TextFlow(
t("العربية", Color.GREEN),
t(" ", Color.YELLOW)
or
flow = new TextFlow(
t(" ", Color.YELLOW),
t("العربية", Color.GREEN)
all the spaces will have negative value obtained from the native function
`CTRunGetPositionsPtr` using `CTGlyphLayout` class.
To make all the negative value positive, I'm adding the least value to all the
positions so that lowest value becomes 0 and rest of the positions are shifted
by the same offset.
> Since the CT framework can also handle alignments, but FX is not making use
> of this, I think all calculations are done with the standard left alignment.
> It would make sense for spaces that "fall off" the left end (because they're
> "trailing") to have negative values. Similarly, if you did LTR text for `cat
> ` with a right alignment, all glyphs would have negative values, except the
> two trailing spaces that would have positive values.
>
I need to check this case. All the testing I have done is by changing the node
orientation of scene to RTL mode with above mentioned cases. Did not change
text alignments separately.
> So I'm curious to see what happens if you have more than one trailing space
> (eg. ` قطة`) and what `CTRunGetPositions` returns then.
For this arabic text with scene node orientation set to RTL and default text
alignment, trailing spaces get negative values. If the space is added in
leading side, then I see positive values.
-------------
PR Review Comment: https://git.openjdk.org/jfx/pull/1468#discussion_r1630794483
