<Swing Dev> [9] Review request for 8163124 Add floating point API support to javax.swing.text.Caret

[Alexandr Scherbatiy]

Suppose there is a text area with two lines with the same text:
abcdefghij
abcdefghij

The char 'c' on the fist line has offset 2 and some coordinates (x1, y1) 
where x1 can have a floating point values like 21.25.
The char 'c' on the second line has offset 13 and coordinates (x2, y2) 
where x2 is equal to x1.

Setting the caret to the first 'c' character sets the magic caret 
position to  (round (x1), round (y1)) position.
Pressing the arrow down key calculates the new  y position and uses the 
x position from the magic caret position which is round(21.5) = 21.
Now the new offset can be calculated as textComponent.viewToModel(new 
Point(21, newY)) which returns offset 12 for char 'b' on the second line 
instead the offset 13 for char 'c'.

Thanks,
Alexandr.

On 8/9/2016 11:32 PM, Philip Race wrote:
> But characters are of varying width. Being on the "20th" char on line N
> may mean being on the "25th" on line N+1.
>
> So I am claiming this is nothing new and we really do not need do 
> anything here.
>
> -phil.
>
> On 8/9/16, 1:06 PM, Alexandr Scherbatiy wrote:
>> On 8/9/2016 12:44 AM, Phil Race wrote:
>>> I was not familiar with this "magic caret" but from reading it seems 
>>> like it has just one use/purpose.
>>> In the event that someone has multi-line text that you can navigate 
>>> around with up/down arrow keys
>>> and that text has lines of varying length, you want a "preferred" 
>>> horizontal position for the caret
>>> to be remembered so the caret is placed at that position whenever 
>>> the line of text has a length
>>> greater than the caret position. Is there anything more to it than 
>>> that ?
>>>
>>> Obviously the caret needs to be placed correctly in the context of 
>>> the text, so the precise position,
>>> even in an all-integer world, is not going to line up on every 
>>> single line, unless you have monospaced text.
>>> ie the "pixel" position is going to get converted into a position on 
>>> the leading or trailing edge of some glyph
>>>
>>> So I wonder, does adding float matter .. is the extra precision 
>>> valuable here ?
>>   It may depend on the rounding of a point position.
>>   Suppose there are two lines with the same text. The caret is on the 
>> first line can have x position N.25. Pressing down the arrow key can 
>> round it to the N and the caret can be set to a previous char on the 
>> second line.
>>
>>   Thanks,
>>   Alexandr.
>>
>>>
>>> -phil.
>>>
>>> On 08/04/2016 05:44 AM, Alexandr Scherbatiy wrote:
>>>>
>>>> Hello,
>>>>
>>>> Could you review the fix:
>>>>   bug: https://bugs.openjdk.java.net/browse/JDK-8163124
>>>>   webrev: http://cr.openjdk.java.net/~alexsch/8163124/webrev.00
>>>>
>>>>   The text position can have floating point value on HiDPI display. 
>>>> The Caret interface should be updated to allow use floating point 
>>>> positions.
>>>>
>>>>   The fix adds the following public API with floating point positions:
>>>>   javax.swing.text.Caret.getMagicCaretPosition2D()
>>>>   javax.swing.text.Caret.setMagicCaretPosition2D(Point2D p)
>>>>   javax.swing.text.JTextComponent.modelToView2D(int pos)
>>>>   javax.swing.text.JTextComponent.viewToModel2D(Point2D pt)
>>>>   javax.swing.text.ParagraphView.getClosestPositionTo(int pos, 
>>>> Position.Bias b, Shape a, int direction, Position.Bias[], int 
>>>> rowIndex, float x)
>>>>
>>>>
>>>>   The fix replaces 
>>>> Caret.getMagicCaretPosition()/setMagicCaretPosition(Point p) to 
>>>> Caret.getMagicCaretPosition2D()/setMagicCaretPosition2D(Point2D p) 
>>>> in all places
>>>>   except DefaultCaret because DefaultCaret extends Rectangle so its 
>>>> coordinates always have int values.
>>>>   I have filled a separated enhancement for this JDK-8163174 Add 
>>>> DefaultCaret2D which supports floating point API
>>>>
>>>>   To make a custom caret use floating point API it is also 
>>>> necessary that PlainView.modelToView() returns a rectangle with 
>>>> floating point values. It can be done after the fix
>>>>     JDK-8156217 Selected text is shifted on HiDPI display
>>>>   which implements Utilities.getTabbedTextWidth(Segment s, 
>>>> FontMetrics metrics, float x, TabExpander e, int startOffset) method.
>>>>   I have filled a separated issue on it:
>>>>     JDK-8163175 PlainView.modelToView() method should return 
>>>> Rectangle2D
>>>>
>>>>  Thanks,
>>>>  Alexandr.
>>>
>>