RFR: JDK-8298060: Fix precision bug in gesture recognizer classes

[John Hendrikx]

On Mon, 12 Dec 2022 16:51:01 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> This includes a fix for the precision problem we've found as part of the graphics warnings clean ups.
>> 
>> I've included two commits, one with just the minimal fix, and one with the clean ups. I can drop off the 2nd commit if it is deemed to be of no added value.
>
> modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/RotateGestureRecognizer.java line 60:
> 
>> 58:             String s = System.getProperty("com.sun.javafx.gestures.rotate.threshold");
>> 59:             if (s != null) {
>> 60:                 rotationThresholdDegrees = Double.valueOf(s);
> 
> should we catch a NumberFormatException and re-throw it with a meaningful text message?  Or the current behavior is ok?
> 
> ditto on line 64

I suppose that would be out of scope for this PR.  I agree though that it would be good to mention that the double that couldn't be parsed is the one we got from `System.getProperty("com.sun.javafx.gestures.rotate.threshold")` as otherwise the error would mean nothing to anyone.

> modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/ScrollGestureRecognizer.java line 252:
> 
>> 250:                         factorX = deltaX / scrollMagnitude;
>> 251:                         factorY = deltaY / scrollMagnitude;
>> 252:                         initialInertiaScrollVelocity = scrollMagnitude / nanosPassed * NANOS_TO_SECONDS;
> 
> is this correct?  shouldn't it be `scrollMagnitude / (nanosPassed * NANOS_TO_SECONDS)`?

I think it's correct, unless you have reason to believe why it wouldn't be.  `scrollMagnitude` is a double, and the division and multiplication that follow it will be all done as doubles.

> modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/ZoomGestureRecognizer.java line 277:
> 
>> 275: 
>> 276:                         if (nanosPassed > INITIAL_VELOCITY_THRESHOLD_NANOS) {
>> 277:                             initialInertiaZoomVelocity = (totalZoomFactor - prevTotalZoomFactor) / nanosPassed * NANOS_TO_SECONDS;
> 
> `(totalZoomFactor - prevTotalZoomFactor) / (nanosPassed * NANOS_TO_SECONDS);` ?

The order is irrelevant, it could as well be `((totalZoomFactor - prevTotalZoomFactor) / nanosPassed) * NANOS_TO_SECONDS` -- I'll let the compiler decide what is more optimal.

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PR: https://git.openjdk.org/jfx/pull/966