fillOpacity=1 does not create a completely opaque/solid fill for point marks

[joelostblom]

It seems like setting fillOpacity=1 does not make points completely opaque. This is in contrast to setting opacity=1 which does have this effect. It is not that fillOpacity has no effect at all, lower values makes the fill more transparent, it just seems that the scale is shifted, which is confusing. I would expect fillOpacity=1 to make the fill of the points completely solid/opaque, just as opacity=1.

fillOpacity=1:

Open the Chart in the Vega Editor

opacity=1

Open the Chart in the Vega Editor

[kanitw]

This is probably not a bug. I think, by design, Vega makes opacity/fillOpacity behavior consistent with SVG and Canvas.
https://stackoverflow.com/questions/37759898/opacity-vs-fill-opacity-in-svg

In any case, I'll move this ticket to Vega repo.

[jheer]

This is a Vega-Lite issue, as Vega-Lite is producing outputs with conflicting opacity and fillOpacity (see image). Vega is simply translating those down to SVG/Canvas as designed. I'll reassign back to the VL repo.

[domoritz]

We should probably not generate the default opacity for point marks when there is an explicit fillOpacity.

[kanitw]

@joelostblom relevant code is here

I think it's probably safe to say we shouldn't set the default opacity if there is fillOpacity there.