Remove remaining hairline between bars in bar chart

[cstork]

Hi! Below I tried my best to eliminate the space between the bars of a bar chart (without resorting to defining the width in pixels). What am I missing?

source = pd.DataFrame({
    'a': ['2025-01-01 00:01', '2025-01-01 00:02', '2025-01-01 00:03', '2025-01-01 00:04', '2025-01-01 00:05'],
    'b': [28, 55, 43, 91, 81]
})

alt.Chart(source, width=100).mark_bar(
    width=alt.RelativeBandSize(1)
).encode(
    alt.X('hoursminutes(a)').axis(grid=False).scale(padding=0),
    alt.Y('b')
)

[kgoodrick-uu]

You can remove the gap by setting binSpacing to 0.

source = pd.DataFrame({
    'a': ['2025-01-01 00:01', '2025-01-01 00:02', '2025-01-01 00:03', '2025-01-01 00:04', '2025-01-01 00:05'],
    'b': [28, 55, 43, 91, 81]
})

alt.Chart(source, width=100).mark_bar(
    width=alt.RelativeBandSize(1),
    binSpacing=0
).encode(
    alt.X('hoursminutes(a)').axis(grid=False).scale(padding=0),
    alt.Y('b')
)

[cstork]

Yes, but that would mean resorting to defining the width in pixels, which I want to get away from. (See my original question.) ...or am I missing some smart way to set size in some parametrized fashion?

[kgoodrick-uu]

I am not able to reproduce the gap while still using binSpacing, see this example in the Vega Editor. Even with different themes there is no gap.

[cstork]

Thanks for all your prompt answers! @kgoodrick-uu I looked at your vega editor graph and I think I know what's going on. In Chrome (Win & Mac) I saw:

However, then I checked using Firefox (Win & Mac) and Safari and the hairlines was gone! So, I guess, it boils down to the browser's rendering engine. :-/

I'm still curious if doing something with discreteBandSize would fix it for Chrome, though...

[joelostblom]

I believe you are running into this rendering issue stemming from Vega vega/vega#3980. It's quite unhelpful that chart appearance is not guaranteed to be consistent across browser so if you have anyone here have any pointers on how to solve the spacing issue, feel free to chime in there.

[cstork]

Oh, and I see you had already opened a similar issue for Vega-Lite, too.

I'll mark this as answered since @kgoodrick-uu's answer would fix this without this issue/bug on Chrome.