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

[Sergey Bylokhov]

On 27.04.16 6:17, Philip Race wrote:
> Applications cannot change the device transform and expect the same user
> space
> metrics unless they specify fractional metrics to be ON.
>
> In your example below you may already have a scaled graphics context
> if you were printing (for example).

Do we have the difference between device scale, and full scale(device 
scale+user scale)? I guess we have only two transforms on the low level:
  - Font transform
  - Full transform(device + user).
So from the application point of view there is no difference the scale 
was changed by device or by the application.

> Changing what happens in the font system is not an option since it
> will break many applications - even if it were the right thing to do -
> which it is not.

I do not think that the spaces will be poor, especially if the new 
rounding will be closer to the correct values in floats.

>
> -phil.
>
>
>
>
>
> On 4/26/16, 4:49 PM, Sergey Bylokhov wrote:
>> On 27.04.16 1:50, Phil Race wrote:
>>> Glyphs are always rasterised in device space so it does mean device
>>> space.
>>
>> I don't argue with it, the question is how to round.
>>
>>> The identity transform therefore happens to always return a user space
>>> advance is that is an integer, but it is not bound to be so under any
>>> other transform.
>>
>> I am not sure that this is correct. The simple example:
>>
>> BufferedImage bi = new BufferedImage(width, height,TYPE_INT_ARGB);
>> int length = g2d.getFontMetrics().stringWidth(TEXT);
>> Graphics2D g2d = bi.createGraphics();
>> g2d.scale(2, 2);
>> length = g2d.getFontMetrics().stringWidth(TEXT);
>>
>> In what space will be the length? I assume that this is the user
>> space. Note that if in the second time we get 13 pixels we will round
>> it to 7 (but rendering will be done to 6.5 * 2 = 13). My suggestion in
>> the fix is to make this round on the lower level and use the same
>> values as stringWidth() and during rendering.
>>
>>>
>>> -phil.
>>>
>>> On 04/26/2016 03:28 PM, Sergey Bylokhov wrote:
>>>> On 27.04.16 0:34, Phil Race wrote:
>>>>> Fractional metrics being "off" does not mean that *user space*
>>>>> advances
>>>>> need to be integers,
>>>>> it refers to *device* space advances. Of course if your API does not
>>>>> support floats you have a
>>>>> problem - particularly if - you are character advance adding in which
>>>>> case it is better to ask the
>>>>> font system for the overall advance of the text.
>>>>> https://docs.oracle.com/javase/8/docs/api/java/awt/RenderingHints.html#KEY_FRACTIONALMETRICS
>>>>>
>>>>>
>>>>
>>>> The documentation says that in case of "fm-off" the "simplified system
>>>> based on integer device positions is typically used" + "rounding
>>>> advance widths for rasterized glyphs to integer distances", it does
>>>> not say that the "integer distance" should be rounded to the nearest
>>>> device/pixel. It says that "rounding operations as the high quality
>>>> and very precise definition of the shape and metrics of the character
>>>> glyphs must be matched to discrete device pixels" I guess we should
>>>> confirm the specification because results of the fix will be "discrete
>>>> number of device pixels", isn't it?
>>>>
>>>
>>
>>


-- 
Best regards, Sergey.