RFR: 8282290: TextField Cursor Position one off

[Andy Goryachev]

On Wed, 15 Nov 2023 18:20:14 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> The change listener on caretPositionProperty() was not getting invoked on replacing the content with same text as there was no change in caret position. Since the textProperty invalidation sets the forward bias to true by default, incorrect caret position was  calculated when the same text was replaced after clicking on the trailing edge of last character or empty space in the TextField.
>> 
>> Since caretShapeProperty invalidation listener gets invoked without changing the caret position, updating the caretBiasProperty on this listener solves the issue.
>> 
>> Since the caret position value will be same when the caret is present after the last character or before the last character, it can not be validated using unit test.
>> The fix can be validated using MonkeyTester.
>> Steps to select TextField option in Monkey Tester.
>> 
>> - Open the MonkeyTester app and select TextField from the left option pane.
>> - Select Short from Text selection option and click on the TextField to bring it into focus.
>> - Select all using cmd(ctrl) + a and copy using cmd(ctrl) + c
>> - Click on empty space in the TextField after the present content.
>> - Select all again using the keyboard shortcut and paste using cmd(ctrl) + v
>> - The caret should be displayed after the last character. Without the fix caret gets displayed before the last character.
>
> modules/javafx.controls/src/main/java/javafx/scene/control/skin/TextFieldSkin.java line 248:
> 
>> 246:         textNode.caretShapeProperty().addListener(observable -> {
>> 247:             caretPath.getElements().setAll(textNode.caretShapeProperty().get());
>> 248:             if (caretPath.getElements().size() == 0 || caretPath.getElements().size() != 4) {
> 
> I think this can be simplified to:
> 
> 
> if (caretPath.getElements().size() != 4) {
>     // The caret pos is invalid.
>     updateTextNodeCaretPos(control.getCaretPosition());
> } else {
>     caretWidth = Math.round(caretPath.getLayoutBounds().getWidth());
> }

this might be problematic, as it uses undocumented aspect of Text/Flow.caretShape().  the current implementation returns either a single line, or two lines (moveto,lineto,moveto,lineto) in the case of split/dual caret.  But this may not be true in the future!  If we add a directional indicator to the caret this logic will break.

What we may need is to invent a new API possibly that gives us more information about the caret - whether it's a single or split one, or whether it has a directionality indicator, information about the adjacent text segments (rtl,ltr), etc.

We can keep this logic for now, to be fixed once (and if) we add the more detailed caret API.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1287#discussion_r1394656378