Allow for easing functions on transform

[TimVanMourik]

Feature request

Especially on a 'zoom to fit', it would be pretty neat if you could specificy a transition and a maybe a transition-ease-function.

Specifically, viewer.js would need to be updated:

react-svg-pan-zoom/src/viewer.js

Lines 358 to 360 in 334de3a

	<g
	transform={toSVG(value)}
	style={blockChildEvents ? {pointerEvents: "none"} : {}}>

One way to support this is with a transition prop in seconds and maybe an easeFunction prop with option as EASE_IN_OUT, EASE_LINEAR, etc.

I can give it a shot, if you want, if you have name a preferred implementation.

[chrvadala]

It seems a good feature, we might introduce a new prop to manually enable this extra feature. I was wondering if using a css transition is enough.
Feel free to start with a PR ;)

[krnlde]

CSS transition unfortunately add a huge delay. I didn't quite understand why. You don't see any animation until you stop panning / zooming. Also CSS transitions don't feel very natural since the momentum/inertia is not calculated.

Here's the CSS I used:

.pan-zoom-wrapper > svg > g {
  transition: transform .1s ease-out;
}

A class to determine the transforming <g> element would be helpful to better select that.

[kriwi-jtpln]

I recently ran into the same problem with the css transitions. What worked for me was to disable the transition during manual drag and zoom and use a state to add a class to the pan-zoom-wrapper. Its a hack but does the job.

<ReactSVGPanZoom
              ...
              className={`ReactSVGPanZoom ${renderWithTransition ? 'with-transition' : ''}`}
              onMouseDown={() => setRenderWithTransition(false)}
              onTouchStart={() => setRenderWithTransition(false)}
>

...and enable the class again when using fitToViewer or others

const onFitToViewer = () => {
    setRenderWithTransition(true)
    panZoomRef.current.fitToViewer(ALIGN_CENTER, ALIGN_CENTER)
  }

And big thanks for this great library.

[ulo]

Hi, I would love to get a smooth scrolling by using transitions!
However, CSS transitions somehow do not work for me... I guess it is because the transform is an SVG attribute and not CSS.
Moving to CSS transformation, i.e. from

<g 
   transform={toSVG(value)} 
   style={blockChildEvents ? {pointerEvents: "none"} : {}}>

to

<g 
   style={blockChildEvents ? {pointerEvents: "none"} : { transform: toSVG(value), transition: "transform ease 0.1s" }}>

works very nice and very smooth for the zoom!

But does not really work for pan...