[OpenJDK 2D-Dev] [9] Review request for 8142966 Wrong cursor position in text components on HiDPI display

[Jim Graham]

Isn't the problem there that we are returning an integer as the advance? 
  Why aren't we returning 7.35 as a value instead of 8?

Also, shouldn't 7.35 round to 7 and 14.7 round to 15?

				...jim

On 2/6/2016 7:28 AM, Alexander Scherbatiy wrote:
> On 05/02/16 23:39, Phil Race wrote:
>> Two things strike me when I read this
>>
>> 1) Initial surprise at how deep into the font code it goes.
>> Perhaps there are alternatives.
>>
>> 2) That it changes to using the linear metrics for measuring advance.
>> Regardless of (1) I do not think (2) is correct. I am fairly sure this
>> will lead to changes in text advance. It seems like it must throw
>> away adjusted metrics as a result of glyph hinting.
>>
>> I don't know what the fix should be, since I have not looked at the
>> problem top-down, I am just seeing the bottom-up proposed solution.
>> So all I can say for now is that it needs to be at least somewhat
>> different.
>
>    There was the same issue on Mac OS X which has been fixed in the
> similar way:
>    8013569 [macosx] JLabel preferred size incorrect on retina displays
> with non-default font size
>      https://bugs.openjdk.java.net/browse/JDK-8013569
>      http://cr.openjdk.java.net/~serb/7190349/webrev.04/
>
>    The problem is that in many case for UI scale 2 we return to a user
> an unscaled value.
>    But a value for transformed glyph advance, rounded and descaled can
> differ from just rounded glyph advance.
>
>   For example, font[dialog, plain, 12] char 'a':
>   transform: 12, advance: 7.35,  rounded advance: 8
>   transform: 24, advance: 14.70 round advance: 14
>
>   and 8 does not equal 14 / 2.
>
>    The solution for Mac OS X was to get the glyph advance using only
> font transform, round it and then apply the dev transform:
>
> CGGlyphImages.m:
>   481     advance = CGSizeApplyAffineTransform(advance, strike->fFontTx);
>   482     if (!JRSFontStyleUsesFractionalMetrics(strike->fStyle)) {
>   483         advance.width = round(advance.width);
>   484         advance.height = round(advance.height);
>   485     }
>   486     advance = CGSizeApplyAffineTransform(advance, strike->fDevTx);
>
>    Thanks,
>    Alexandr.
>>
>> -phil.
>>
>> On 01/27/2016 01:26 PM, Alexander Scherbatiy wrote:
>>>
>>> Hello,
>>>
>>> Could you review the fix:
>>>   bug: https://bugs.openjdk.java.net/browse/JDK-8142966
>>>   webrev: http://cr.openjdk.java.net/~alexsch/8142966/webev.00/
>>>
>>>  The proposed fix rounds a glyph advance first and then scales it if
>>> UI scales do not equal to one.
>>>
>>>  Thanks,
>>>  Alexandr.
>>>
>>
>