[External] : Aw: Re: JavaFX snapping and scale

[Kevin Rushforth]

By the time it is rendered, it will be transformed into the scaled 
space. So the actual coordinate in screen space will be 13.

-- Kevin

On 10/1/2021 7:26 AM, Marius Hanl wrote:
> Thanks for your answer.
> Then one more question: How is a non-integer value rendered then?
> Say we have snapped x value of 10.4 (scale 1.25). As we can just 
> render on a whole pixel, what will happen?
> - Marius
> *Gesendet:* Dienstag, 28. September 2021 um 01:57 Uhr
> *Von:* "Kevin Rushforth" <kevin.rushforth at oracle.com>
> *An:* openjfx-dev at openjdk.java.net
> *Betreff:* Re: JavaFX snapping and scale
> The basic idea behind snapping to pixel boundaries (which is optional,
> but on by default) is that 2D primitives will look more crisp if they
> are rendered on whole pixel boundaries. When there is no HiDPI involved,
> the operation of snapping to a pixel boundary can be done with a simple
> floor, round, or ceil operation (depending on what you are snapping).
> When there is a HIDPI scale involved, the value in user space needs to
> be chosen such that the transformed value ends up on a pixel boundary.
> That's why you will see snapped values that aren't on integer boundaries
> when the HiDPI scale is, say 1.25.
>
> In the case you ran into, the problem might be that the snapping isn't
> happening in the right place in the computation. Also, it seems quite
> possible that the clipping isn't being calculated correctly with respect
> to pixel snapping.
>
> You can take a look at JDK-8211294 [1] which was fixed by PR #308 [2]
> for a recent example of a HiDPI bug affecting ScrollPane that was fixed.
> There are a couple of follow-on issues that came out of that issue,
> although I suspect they aren't relevant to the bug you are looking at.
>
> -- Kevin
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8211294 
> <https://bugs.openjdk.java.net/browse/JDK-8211294>
> [2] https://github.com/openjdk/jfx/pull/308 
> <https://urldefense.com/v3/__https://github.com/openjdk/jfx/pull/308__;!!ACWV5N9M2RV99hQ!YDG10_6aLWHF6oDpo3JIKfgBDwkjcbFb75u8jaIuZp0zCY0tmAExinA93yn4H6gdZzIT$>
>
> On 9/27/2021 2:41 AM, Marius Hanl wrote:
> > I recently tried to fix "TableView: visual glitch at borders on
> > horizontal scrolling".
> > Ticket: [1]https://bugs.openjdk.java.net/browse/JDK-8218745 
> <https://bugs.openjdk.java.net/browse/JDK-8218745>
> > PR: [2]https://github.com/openjdk/jfx/pull/630 
> <https://urldefense.com/v3/__https://github.com/openjdk/jfx/pull/630__;!!ACWV5N9M2RV99hQ!YDG10_6aLWHF6oDpo3JIKfgBDwkjcbFb75u8jaIuZp0zCY0tmAExinA93yn4H8fP3AKI$>
> >
> > As also written in the PR I have problems understanding the
> > snapping/scaling of JavaFX.
> > Here in short what I found out:
> > - Snapping fixed the issue for a scale of 1 or 2, but not for a scale
> > like 1.25 or 1.5
> > --- Also VirtualFlow is the only occurence where we set the layoutX of
> > a clip (might be the problem?)
> > - This visual glitch only happens sometimes when the x value is a
> > decimal number, e.g. 12.66 (never when it's a round number like 13)
> > - Math.round(..) or a cast to int fixed this (for all scales), but is
> > probably not the correct solution or maybe only fixing a symptom here
> >
> > Which leads to my question where may some of you can help me:
> > - How does JavaFX renders a node when e.g. x is a decimal number? How
> > many pixel are used then?
> > - And does a decimal number make sense (Why we e.g. don't round the
> > value), which looks like it works fine and doesn't result in visual
> > glitches
> >
> > Also information/insights about fixes made in the past which relates
> > with this are welcome.
> > I saw that there were quite some issues with a scale other then 1 in
> > the past.
> >
> > Note: If the result is that everything works as expected chances are
> > there might a generic problem with snapping/layout/rendering somewhere
> > then.
> > Any information are welcome and feel free to also have a look at the
> > PR.
> >
> > -- Marius
> >
> > References
> >
> > 1. https://bugs.openjdk.java.net/browse/JDK-8218745 
> <https://bugs.openjdk.java.net/browse/JDK-8218745>
> > 2. https://github.com/openjdk/jfx/pull/630 
> <https://urldefense.com/v3/__https://github.com/openjdk/jfx/pull/630__;!!ACWV5N9M2RV99hQ!YDG10_6aLWHF6oDpo3JIKfgBDwkjcbFb75u8jaIuZp0zCY0tmAExinA93yn4H8fP3AKI$>