BQPlot 0.12.12 Stacked bar opacities set on a group level and not individual bars

Hi team,

There’s a change in behaviour between bqplot 0.11.6 and 0.12.12 where setting opacities for a stacked bar plot applies the opacities on the entire bar group (all layers) in version 0.12.12, as opposed to each individual bar layer in 0.11.6. The expected behaviour is that of 0.11.6. See the code below to reproduce:

from bqplot import OrdinalScale, LinearScale, Bars, Axis, Figure

x_ord = OrdinalScale()
y_sc = LinearScale()

bar = Bars(x=[0, 1], y=[[1.5, 1.5], [2.5, 2.5], [3.5, 3.5]], 
           scales={'x': x_ord, 'y': y_sc}, 
           labels=['Dim 1', 'Dim 2', 'Dim 3'], display_legend=True, opacities=[1, 0.7, 0.1, 0.1, 0.7, 1])
ax_x = Axis(scale=x_ord)
ax_y = Axis(scale=y_sc, orientation='vertical')

Figure(marks=[bar], axes=[ax_x, ax_y])

This is a screenshot from version 0.11.6, with the expected behaviour:

That is a screenshot from 0.12.12, where opacities are applied group-wise:

Many thanks

[ibdafna]

I think that makes sense. We can also use “no_group” to say we’re not applying any sort of grouping logic. I’m okay with either! Feel free to make the call 😃

[martinRenou]

I updated my PR. Please tell me what you think 😃