Altair 4.1 "scale_factor" seems to do nothing

[zacharylawrence]

Using Altair 4.0, I'm able to adjust the resolution of an output PNG with scale_factor:

chart.save("filename.png", scale_factor=2.0)

In Altair 4.1, adjusting scale_factor doesn't seem to change the output resolution.

Is this possibly related to altair_saver?

As referenced here: https://altair-viz.github.io/user_guide/saving_charts.html#figure-size-resolution

[jakevdp]

Altair 4.1 changed it's save to use altair_saver under the hood, so this bug is likely related to failing to plumb that value through correctly.

[jasonrwang]

@taralloc's PR fixes the resolution issue for me, but now I get weird spacing between characters.

New

Old

(I'm on Node v10.24.1, Altair 4.1, Altair Saver 0.5.0 with adjustment; macOS 11.2.3).

[baldwint]

Using @taralloc's branch also fixed it for me. I did not observe any strange spacing between characters.

node v15.4.0, altair 4.2.0, python 3.9.2, macOS 10.14.6.

[joelostblom]

This has been fixed in Altair's development branch by switching to vl-convert for saving images. It is still an issue for altair_saver which is tracked in #2191