I'm working on a vega-lite project where I'd like a selection to be made with a click, and updated by dragging the selection. As a concrete example see this adaptation of Jake Vanderplas’s Multi-Value Tooltip in Vega-Lite. A selection can be made with a single click, and a click drag results in the selection moving.
As implemented in the example, I found merging a mousedown with a mousemove event gave me this desired interaction for mouse events:
"on": "mousedown, [mousedown, mouseup] > mousemove"
Now, I'd like this to work similarly on touch devices, so that a selection can be made with a touch, and is updated through a touch drag. I tried a similar approach of merging a touchstart and touchmove event:
"on": "mousedown, [mousedown, mouseup] > mousemove, touchstart, [touchstart, touchend] > touchmove"
But this doesn't seem to work on either my iPhone or with touch simulation in Firefox Developer Tools. In both cases, a touch makes a selection but dragging doesn't update the selection.
Any ideas on why this isn't working, or how to achieve the interaction I want?