RFR: 8304831: TextFlow.hitTest.insertionIndex incorrect with surrogate pairs

[Kevin Rushforth]

On Fri, 14 Apr 2023 07:35:33 GMT, Karthik P K <kpk at openjdk.org> wrote:

> Since surrogate pairs are internally considered as 2 characters and text field is null in `HitInfo` when `getInsertionIndex` is invoked from `TextFlow`, wrong insertion index was returned.
> 
> Updated code to calculate insertion index in `getHitInfo` method of `PrismTextLayout` class when `hitTest` of trailing side of surrogate pair is requested. Since text runs are processed in this method already, calculating the insertion index in this method looks better than calculating in `getInsertionIndex` of `HitInfo` method.
> The latter approach also requires the text to be sent to `HitInfo` as parameter from the `hitTest` method of `TextFlow`. If the number of `Text` nodes in `TextFlow` are very large, processing all the `Text` nodes on each `hitTest` method invocation might cause performance issue. Hence implemented first approach.
> 
> Added system test to validate the fix.

Reviewers: @prrace @andy-goryachev-oracle

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PR Comment: https://git.openjdk.org/jfx/pull/1091#issuecomment-1509816515