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[bot]]

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[openjdk[bot]]

@mstr2 This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

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

Reviewed-by: angorya, kcr

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At the time when this comment was updated there had been 20 new commits pushed to the master branch:

• 9a4b601a7d3ea0ddfb001d27eecdc2ee4185298c: 8365402: Bump minimum JDK version for JavaFX to JDK 24
• 368bd20b887bb813718fbfecc14760597e8d4521: 8322486: ColorPicker: blurry popup
• fa2127cb3a3fc11238c5c8ce4cf0d15c4000f05c: 8365576: Temporarily make Metal the default JavaFX rendering pipeline for macOS
• ... and 17 more: https://git.openjdk.org/jfx/compare/bc433da812461a1c2796cdb3123f814e4ce532d5...master

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[openjdk[bot]]

@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[bot]]

@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[bot]]

Webrevs

• 04: Full - Incremental (24d5afd4)
• 03: Full - Incremental (a7aacb95)
• 02: Full - Incremental (26208229)
• 01: Full - Incremental (92d06d7e)
• 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.

[mstr2]

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.

Can I interest you in a review of the API and/or the implementation?

[bridgekeeper[bot]]

@mstr2 This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply issue a /touch or /keepalive command to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

[palexdev]

Currently the workaround I use for this is to have a custom Interpolator implementation like:

public class Cubic extends Interpolator {
    private final double x1;
    private final double y1;
    private final double x2;
    private final double y2;

    private static final double CUBIC_ERROR_BOUND = 0.001;

    public Cubic(double x1, double y1, double x2, double y2) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
    }

    double elevateCubic(double a, double b, double m) {
        return 3 * a * (1 - m) * (1 - m) * m +
               3 * b * (1 - m) * m * m +
               m * m * m;
    }

    @Override
    public double curve(double t) {
        double start = 0.0;
        double end = 1.0;
        while (true) {
            final double midpoint = (start + end) / 2;
            final double estimate = elevateCubic(x1, x2, midpoint);
            if (Math.abs(t - estimate) < CUBIC_ERROR_BOUND) {
                return elevateCubic(y1, y2, midpoint);
            }
            if (estimate < t) {
                start = midpoint;
            } else {
                end = midpoint;
            }
        }
    }
}

Which allows me to define such curves:

    public static final MotionPreset EXPRESSIVE_FAST_SPATIAL = MotionPreset.of(
        new Cubic(0.42, 1.67, 0.21, 0.90),
        MEDIUM3 // Duration constant
    );

I believe I copied this from Flutter. (The new Material 3 Expressive makes use a lot of springs, see Material 3 Docs)

Unfortunately, I need to use such curves in CSS too, so I kinda need this commit to be merged

[kevinrushforth]

The API spec changes look good. I left a comment in the CSR that you need to add the changes made to RadialGradient (it looks good otherwise).

I spot checked the implementation and it all looks like what I expect. I'll finish reviewing and testing today.

[mstr2]

/integrate

[openjdk[bot]]

Going to push as commit 999c396d3c8d76be5b25c08e66490f026ae7b99a. Since your change was applied there have been 20 commits pushed to the master branch:

• 9a4b601a7d3ea0ddfb001d27eecdc2ee4185298c: 8365402: Bump minimum JDK version for JavaFX to JDK 24
• 368bd20b887bb813718fbfecc14760597e8d4521: 8322486: ColorPicker: blurry popup
• fa2127cb3a3fc11238c5c8ce4cf0d15c4000f05c: 8365576: Temporarily make Metal the default JavaFX rendering pipeline for macOS
• ... and 17 more: https://git.openjdk.org/jfx/compare/bc433da812461a1c2796cdb3123f814e4ce532d5...master

Your commit was automatically rebased without conflicts.

[openjdk[bot]]

@mstr2 Pushed as commit 999c396d3c8d76be5b25c08e66490f026ae7b99a.

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