JDK-8130738 TextFlow's tab width is static
swpalmer at gmail.com
Thu Oct 17 17:40:39 UTC 2019
Thanks for taking a look. I was going to get back to this soon to attempt adding the CSS property as you mention in your previous email. I considered tabSize as a name as well. I don’t have a preference if we leave things as representing tabs as a number of spaces. But it wouldn’t be too difficult to support units, making it mostly compatible with CSS rules. The way I envision that is having two properties, tabSize and tabUnit.
David mentioned javafx.css.SizeUnits… I looked quickly at the java docs for it, and it’s basically undocumented . So I went to https://www.w3.org/TR/css-values-3/#lengths and I see there is no CSS unit like ‘ems’ but meaning the width of a space in the current font. The problem with that is it would leave out the possibility to set the tab width to anything relative to the current implementation of 8 spaces. (In hindsight it should have been implemented based on ‘ems’, which for a fixed width font as typically used in a code editor would be the same as 8 spaces anyway)
Do we add something to SizeUnits so we can work around this? e.g. ‘fxsp’ (FX-space - fx prefix to avoid a potential collision with any future official CSS units)
// Two tab-related properties
public void setTabSize(int size); // defaults to 8
public void setTabUnits(SizeUnits units); // ?? no unit for width of space in current font
If we did the above, I would consider adding this for convenience:
public void setTabWidth(int size, TabUnits units);
As far as setting a range, I’m not sure there is any worthwhile benefit to enforcing a maximum. If we want to store the value in a short instead of an int to potentially save a couple bytes, sure. Otherwise, if someone wants to set tabs to be 20 spaces or 100, why should we prevent it? If there isn't a performance or memory impact, I wouldn’t enforce a maximum.
Ignoring any out of range values rather than clamping seems fine to me as well. I was thinking of what happens if the value was bound to another value that strayed out of range. Clamping would get you as close as possible to the bound value, rather than stuck at the previously observed value. I just guessed that would be preferred, but if ignoring is more consistent with other values, then I agree it makes sense. As long as the behaviour is documented, I can’t think of any significant downside either way.
> On Oct 17, 2019, at 12:45 PM, Phil Race <philip.race at oracle.com> wrote:
> Some more points which I thought about but for whatever reason did not pen ..
> First one minor thing: tabWidth is an OK name, but it does not
> conjure up that the value you specify isn't a width in pixels but the
> number of discrete space characters to use. FWIW CSS calls it tab-size.
> But CSS then supports pixels and ems .. that complicates matters a lot.
> Thee rest is mostly to do with "legal or sensible values"
> You have :
> if (spaces < 0)
> spaces = 0;
> since negative values are not something we want to support!
> But I think instead of clamping you could "ignore", any out of range value.
> This is practiced elsewhere in FX where illegal values are ignored rather than
> throwing an exception, although it might be that clamping is quite common
> in range cases.
> The follow on to that is that what is a sensible maximum value.
> Currently we have int which is more than we need. For that matter so is short.
> I think we should have a documented and enforced sensible maximum.
> Perhaps it could be "8" meaning we only support reducing tab width as I
> don't know if anyone really wants to increase it.
> CSS doesn't have a limit that I can see but if we are already only supporting
> it described as number of spaces, we can have this other limitation too.
> If you think 8 is too small, then maybe 16 ?
> Also remember we can compatibly relax it later but we can't compatibly tighten it.
> On 10/15/19 12:17 PM, Phil Race wrote:
>> I've looked over this and I don't see any issues - meaning gotchas.
>> It just provides a way to over-ride the hard-coded 8,
>> whether using a Text node directly or a TextFlow.
>> Two observations of what one might call limitations
>> 1) This is a rendering time property, which is controlled by the program.
>> A document containing tabs saved and re-rendered somewhere else
>> won't be helped.
>> 2) This just provides API on the scene graph node types, not any of the UI controls
>> which use Text nodes. Something like a CSS property may be the way to go if
>> you wanted that.
>> Text has a nested class StyleableProperties for CSS properties with which it
>> plays nice : font, underline, strikethrough, text-alignment
>> So creating an fx-tabWidth (or similar name) CSS property could be propagated
>> through to there in a similar way.
>> On 9/30/19 9:48 AM, Scott Palmer wrote:
>>> Okay, current work relocated to a clone of the new official Git repo.
>>> My initial implementation is here:
>>> https://github.com/swpalmer/jfx/commit/cc6193451bf8a693093f3ded5dcbe47af2fcbe8f <https://github.com/swpalmer/jfx/commit/cc6193451bf8a693093f3ded5dcbe47af2fcbe8f>
>>> I would submit it as a pull request but that seems premature since there hasn’t been any real discussion of challenges I’ve overlooked. All I have are the famous last words, “It works for me.”
>>> I saw in the archives a concern about tab width vs tab stops. For some reason I didn’t get the email. Anyway, I don’t think arbitrary tab stop positions, at different intervals that is, are what was asked for. That certainly would require a significantly different implementation.
>>> Would love to keep some momentum going on this before I become busy with other things and won’t have time for it.
>>>> On Sep 23, 2019, at 3:57 PM, Scott Palmer <swpalmer at gmail.com> wrote:
>>>> My current work is here https://github.com/javafxports/openjdk-jfx/compare/develop...swpalmer:jdk-8130738?expand=1 <https://github.com/javafxports/openjdk-jfx/compare/develop...swpalmer:jdk-8130738?expand=1>
>>>> While writing a unit test I realized that the StubToolkit isn’t really running the Prism layout code, so I’m not sure how that gets tested. I made it work with StubTextLayout for now.
>>>>> On Sep 20, 2019, at 12:57 PM, Scott Palmer <swpalmer at gmail.com <mailto:swpalmer at gmail.com>> wrote:
>>>>> Thanks Kevin.
>>>>> My current implementation appears to be working for TextFlow and Text, with the TextFlow overriding the tabWidth of the child Text nodes. This seems to work out naturally from the way TextFlow overrides the TextLayout instance used by the Text node.
>>>>> If there are tricky corner-cases that I’m missing, I guess figuring out all the cases it will need to handle is part of this discussion. It didn’t seem to be that challenging so far, so perhaps I am missing something (hopefully not). I wrote a small test app to visually see that things were working as I expected. I have not yet written the unit tests.
>>>>>> On Sep 20, 2019, at 10:58 AM, Kevin Rushforth <kevin.rushforth at oracle.com <mailto:kevin.rushforth at oracle.com>> wrote:
>>>>>> Hi Scott,
>>>>>> I'm sure Phil will have more comments on this. While the API seems simple enough on the surface, I suspect that this will be a challenging feature to implement correctly for all of the cases it will need to handle. It would need careful review and testing as well. My only comment on the API itself is that if we do accept this feature, it should probably go on both Text and TextFlow, and be one of the attributes of Text that is ignored / overridden when a Text node is in a TextFlow.
>>>>>> -- Kevin
>>>>>> On 9/18/2019 6:14 PM, Scott Palmer wrote:
>>>>>>> I would like to implement this feature, being able to adjust the tab size in a TextFlow or Text node (JDK-8130738 <https://bugs.openjdk.java.net/browse/JDK-8130738 <https://bugs.openjdk.java.net/browse/JDK-8130738>>). It involves new public API, so I want to start a discussion about it here. (My motivation is that RichTextFX suggests an entirely unacceptable workaround of substituting actual spaces when the tab character is typed and cites the lack of this API.)
>>>>>>> I’ve already jumped the gun and taken a crack at an implementation. It is currently incomplete as I was just poking around to see if it was going to be easy enough to not take up too much of my time. It boils down to:
>>>>>>> TextFlow and Text get a new property for tab width, an integer representing the number of spaces taken by a tab. (The value is only used to initialize the tab width for the TextLayout when needed.)
>>>>>>> TextLayout interface gets a new method: boolean setTabWidth(int spaces)
>>>>>>> TextLayout gets a new constant: DEFAULT_TAB_WIDTH = 8;
>>>>>>> PrismTextLayout implements the new setTabWidth API.
>>>>>>> I’m not sure that the Text node needs this new property. I figured it would be rarely used on that class, so I had implemented it via an added property in the private TextAttributes class. Maybe it isn’t needed at all.
>>>>>>> What’s the next step?
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