<Swing Dev> [9] Review request for 8132119 Provide public API for text related methods in SwingUtilities2

[Phil Race]

On 04/19/2016 01:08 AM, Alexandr Scherbatiy wrote:
> On 4/11/2016 4:29 PM, Philip Race wrote:
>>
>>
>> On 4/6/16, 1:23 PM, Alexander Scherbatiy wrote:
>>>
>>> Hello,
>>>
>>> Could you review the updated fix:
>>>   http://cr.openjdk.java.net/~alexsch/8132119/webrev.09
>>>
>>>  - TextUIDrawing interface and its default implementaion 
>>> BasicTextUIDrawing class are added
>>>  - font metrics argument description is updated
>>>
>>> On 31/03/16 23:23, Phil Race wrote:
>>>> Another webrev where you have to slip past 40_ files to get to the 
>>>> two that really matter :-)
>>>> I would have put SwingUtilities2.java and TextUIDrawing.java as the 
>>>> first files.
>>>    Updated.
>>>>
>>>>
>>>> Some of what I have to say here is more along the lines of things 
>>>> to think
>>>> about rather than things that are wrong .. but there are also maybe 
>>>> some things
>>>> that need to be fixed.
>>>>
>>>> Is javax.swing.plaf really the right package for the new class ?
>>>> I suppose it is for the use by the UI classes so maybe its right.
>>>>
>>>> Should the methods be taking "double" instead of "int" for location ?
>>>> This means the measurement APIs too.
>>>> None of the JDK 1.2 text APIs use ints. That is all 1.0 legacy.
>>>> So if Swing internally wants to use ints that is OK but maybe the API
>>>> should be floating point (double).
>>>   The provided methods use Graphics as argument which only has 
>>> drawString(String, int, int) method.
>>>   If it is possible it is better to add the methods with float 
>>> arguments and Graphics2D later.
>>>
>>>> Would that  help hi-dpi at all ?
>>>   The hi-dpi support mostly does not require changes in Swing. What 
>>> it does just scales graphics using default transform from graphics 
>>> configuration.
>>
>> Yes, but in another bug you are dealing with a problem positioning
>> the caret because of (somewhat) similar issues where coordinates have 
>> been
>> rounded to an integral. A floating point value allows you to say that
>> this is 25.5 in user-space, even it if is 51.0 in device space.
>
>    It needs some more investigation.
>
>    What I have now is Swing uses font metrics to calculate a string 
> width (FontMetrics.charsWidth(...)) which sums up float char values.
>    The difference between font metrics used by Swing and font metrics 
> from graphics passed to paint method is that the fist has null frc.tx 
> matrix and the second one has a matrix with scales 2 on HiDPI display.
>    The returned char width by the font metrics with null transform has 
> value 7 for char 'a' (linear advance is 6.67 and xAdvance is 7).
>    The char width for the font metrics with scaled transform is 6.5 
> for the same font and char.  FileFontStrike requests glyph metrics and 
> gets linear advance  13.35 (dev transform is taken into account) 
> xAdvance  13 -  and apply the reverse transform. The result is 13 / 2  
> = 6.5.
>
>   And this bothers me because a result for applying the tx transform 
> and inverting it is different than just use the identity transform. 
> There are definitely problems with advance rounding but it seems they 
> are placed out of the Swing area.
>

  I am not sure if you are implying a bug in the font code, but there is 
none that I see
from the above.

There are several distinct issues here
1) You must specify the device transform, unless you are requesting and 
using linear advances.
2) Linear advance is not generally used by Swing since it implies 
unhinted text
3) Rounding of advances back to user space is OK in the case of hinted 
advances and
     identity transform - ie the traditional Swing case - but in the 
case like that you describe
     where the device pixel advance is 13 for a (2.0,2.0) device scale 
then the translation
     back to user space can't express that accurately if it only has int 
to work with,

If Swing is not using the same device transform in calculating the 
advance as it is when
drawing then that is a bug . That was the point of the comment we added 
below about
obtaining the correct FontMetrics .. our L&Fs should be doing that as 
well as admonishing
others to do so.


>>
>>>
>>>> I suppose it would add over-head since all the existing code uses int
>>>> and we are no worse off and can add double methods later if we want 
>>>> to.
>>>>
>>>>
>>>> Regarding FontMetrics we need to add a caution that is must be a 
>>>> FontMetrics
>>>> *obtained from the correct font and graphics*.
>>>    Updated.
>>>>
>>>>
>>>>  i.e what about attributes on the font such as "tracking" ?
>>>> or on the graphics such as FRACTIONALMETRICS
>>>> It looks like Swing might already fail if that were used.
>>>>
>>>> Look at this code :-
>>>>
>>>>    public static int stringWidth(JComponent c, FontMetrics fm, 
>>>> String string){
>>>>         if (string == null || string.equals("")) {
>>>>             return 0;
>>>>         }
>>>>         boolean needsTextLayout = ((c != null) &&
>>>> (c.getClientProperty(TextAttribute.NUMERIC_SHAPING) != null));
>>>>         if (needsTextLayout) {
>>>>             synchronized(charsBufferLock) {
>>>>                 int length = syncCharsBuffer(string);
>>>>                 needsTextLayout = isComplexLayout(charsBuffer, 0, 
>>>> length);
>>>>             }
>>>>         }
>>>>         if (needsTextLayout) {
>>>>             TextLayout layout = createTextLayout(c, string,
>>>>                                     fm.getFont(), 
>>>> fm.getFontRenderContext());
>>>>             return (int) layout.getAdvance();
>>>>         } else {
>>>>             return fm.stringWidth(string);
>>>>         }
>>>>     }
>>>>
>>>> The only thing Swing is looking at is one TextAttribute and whether 
>>>> we have complex text.
>>>> That is not enough. This is an existing implementation issue but 
>>>> one we should fix here.
>>>> You need to examine all the methods for similar issues.
>>>   I created an enhancement for this:
>>>     JDK-8153662 
>>> SwingUtilities2.drawString()/getStringWidth()/clipString() should 
>>> use more text attributes
>>>       https://bugs.openjdk.java.net/browse/JDK-8153662
>>
>> you mean bug ? I upgraded it to P3 because it matters a lot more now
>> with this public API
>
>   I do not think that it is a bug because the main request was to have 
> methods which draw strings in the same way as it is done by Swing L&Fs.

It seems like a bug to me

> This will allow to have custom UI component which mimic to the 
> standard L&Fs.
>
>   It is also can be considered from the following point of view: is 
> the proposed request to use more text attributes more important for 
> standard Swing L&F or for custom L&F.
>   It seems is not the first case because Swing lives with the current 
> implementation for the long time.
>   For the second case we provide the public TextUIDrawing interface 
> which a developer can override and use any text attributes that are 
> necessary.
>
We aren't talking about a separate API to provide text attributes, we 
are talking about the
ones that are part of the font and the implementation is not respecting.

-phil.