8358820: Allow interpolation outside of range [0,1]

[mstr2]

JavaFX unnecessarily restricts interpolation in the following ways:

1. Interpolatable implementations often clamp intermediate values to the interpolation factor range [0,1].
2. SplineInterpolator doesn't accept Y coordinates outside of [0,1] for its control points. While this was probably done so that the computed interpolation factor doesn't exceed [0,1], the restriction goes far beyond that. For example, the following function is not representable, even though its values are all within the [0,1] range:
   
   
   
   The following function is also not representable, but would be very useful for bouncy animations:
   
   

Fortunately, there is no technical reason why JavaFX can't support the full range of animations that can be represented with a cubic Beziér interpolation function.

This PR includes the following changes:

1. The specification of Interpolatable is changed to require implementations to accept interpolation factors outside of [0,1].
2. All implementations of Interpolatable now correctly return intermediate values outside of [0,1].
3. SplineInterpolator now accepts control points with any Y coordinate.

Here's how the result looks like for the previously unrepresentable interpolation function cubic-bezier(0.34, 2.2, 0.64, 1):

/reviewers 2
/csr

---

Progress

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Issue

• JDK-8358820: Allow interpolation outside of range [0,1] (Enhancement - P4)

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[bridgekeeper]

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[openjdk]

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[openjdk]

@mstr2
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

[openjdk]

@mstr2 has indicated that a compatibility and specification (CSR) request is needed for this pull request.

@mstr2 please create a CSR request for issue JDK-8358820 with the correct fix version. This pull request cannot be integrated until the CSR request is approved.

[mlbridge]

Webrevs

• 00: Full (85aacc4d)

[nlisker]

Noting that this proposed change supersedes the previous changes that were done for for https://bugs.openjdk.org/browse/JDK-8226911. The proposed behavioral change makes sense.