Add DragZoomLayer

[teamdandelion]

DragZoomLayer creates a SelectionBox that powers a drag-to-zoom interaction. When you drag a box, the scales zoom into the bounds drawn out in that box and the box disappears. The zoom can be animated over a variable amount of time (default 750ms) with a custom easing function (default d3.cubic-in-out). Tests included.

[jtlan]

@danmane,

I like the idea here, but I worry it might be a bit too narrowly scoped:

• What if the user wants this effect, but only in X or Y?
• What if the user doesn't want double-click to unzoom?

A more modular implementation might be to have a domain-setter on QuantitativeScale that allows passing in an easing function and duration:

scale.domain(newDomain, easingFunction, duration);

Calling this function in the onDragEnd() callback of a DragBoxLayer could provide the smooth zoom-in behavior. As an added bonus, it could be used with XDragBoxLayer, YDragBoxLayer, and anywhere else a user might want to smoothly transition the domain.

Let us know if you want some help implementing this.

[teamdandelion]

Yes, that does seem like a good API point to have (probably can be useful in other contexts as well).

Re: whether this is too narrowly scoped: I agree it is pretty specific to a particular usecase. I feel that having this code exist in public is still useful though, so that Plottable is a bit more "batteries included" with the ability to just do basic charting-type tasks (eg crosshairs, zooming) in a sane configuration without needing to think about XYDragBoxLayers vs XDragBoxLayers and DragEnd callbacks and so forth. Obviously I love the customizability and that this flexibility exists, but it might be nice to provide a path to simplicity for those who want it.

Maybe one way to tackle this would be to break out repositories, plottable-core and plottable-koans or something, where plottable-koans contains pieces like DragZoomLayer that are a bit narrower in scope but are both useful pieces of code in their own right, and provide examples of how you can use the pieces provided by plottable-core.

Or you could imagine going more modular still and encouraging people to publish this kind of code to bower and keep a registry of "plottable modules" (although now you start to have severe versioning issues if you're ever breaking backcompat, not sure if you are...)

[crmorford]

Hey @danmane,
Just checking in on status -- are you working on this PR, or waiting on us to approve something? I think we only want changes to scales.domain() at this point; the discussion about -core and -koans belongs somewhere else.

Would you like to implement the changes to .domain()? Or should we try to schedule it?

[teamdandelion]

Sorry, I probably won't have time to pay attention to this for a few weeks. If you can take over putting in the domain change that would be great.

[CalvinFernandez]

@danmane landing further changes here #3136 . Thanks!