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

[Phil Race]

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 ?

-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.