Support ppi argument

[joelostblom]

Vega-Lite 5.8 added support for a ppi argument to their CLI in vega/vega-lite#8854. Being able to control the ppi of a figure is quite useful since that would give higher resolution without changing the displayed size (as scale/scale_factor does). Would it be possible to add a similar ppi setting to vega-embed?

[domoritz]

I think it makes sense. We already have scaleFactor and I'm not sure whether we can use ppi in view.toImageURL in

vega-embed/src/embed.ts

Line 475 in 617a57b

const url = await view.toImageURL(ext, scaleFactor);

. Do you know what we need to change to make ppi work?

[joelostblom]

Nope, I'm not sure what to update but thought it would make sense to bring parity here with ppi since scaleFactor already exists as you pointed out.