[External] : Re: Pivot properties [was: Enhancements for JavaFX 18]

[Kevin Rushforth]

I definitely don't like having a "magic" initial value that can't be 
reset, so that won't work. And while we could use NaN as an out of band 
value meaning "computed", that still runs into the problem of allowing 
for the odd case where X is computed and Y is specified.

If we do go with the idea of allowing the coordinates to be a percentage 
of the bounding box, with 0.5 as the default, then we could be informed 
by what ImagePattern does. It defines a "proportional" property as follows:

"a boolean that indicates whether start and end locations are 
proportional or absolute. If this flag is true, the two end points are 
defined in a coordinate space where coordinates in the range |[0..1]| 
are scaled to map onto the bounds of the shape that the pattern fills. 
If this flag is false, then the coordinates are specified in the local 
coordinate system of the node."

That's basically what we are doing if we go with Michael's idea. So if 
we do this, the two boolean properties could be named something like 
scalePivotProportional and rotatePivotProportional, with a default of true.

What do you think?

-- Kevin



On 8/23/2021 7:25 PM, Michael Strauß wrote:
> I think normalized coordinates are a very natural fit for the
> definition of a pivot point, which is why the current default value is
> an implicitly-specified normalized coordinate. Adding general-purpose
> coordinate transformations here feels like bringing a sledgehammer to
> crack a nut.
>
> Having a property with an automagically updated "initial" value is
> quite non-standard behavior for properties. It would appear as if the
> property was bound, yet there's no binding. That's markedly different
> from a Transition's 'from' and 'to' properties, which are standard
> properties with normal behavior. A running transition doesn't bind to
> those properties, it uses a snapshot of their values when the
> transition starts.
>
>
> On Sun, Aug 22, 2021 at 9:55 PM Nir Lisker <nlisker at gmail.com> wrote:
>> Now I understand what you meant. However, the concept of normalized coordinates does not appear anywhere in JavaFX (at least not in these contexts). I still think that coordinate transformations should be handled via dedicated means, like coordinate system transformations are. Maybe when we work on mapped bindings (I forgot that I need to review that) this pain point will be alleviated.
>>
>> Kevin, what if we only set the initial value of the pivot (doesn't matter what the implementation detail is) to the center of the node for backwards compatibility, but if the developer changes it to a custom value then it's on them to compute the value again if they want to go back? The default behavior remains.
>> Another relevant point is that Transitions do something similar with their from_,  to_ and by_ methods. They start with Double.NaN to signal that the value should be ignored. While the developer can reset the value to NaN, it is not something that is likely to happen during, say, an interpolation or as a result of a binding.
>>