alpha about colourvalues HOT 12 CLOSED

It's not a problem; these discussions are important 👍

from colourvalues.

What about a na.alpha to e.g. set all NAs as transparent?

from colourvalues.

<sorry - misread your request>

yes - good idea.

from colourvalues.

@tim-salabim can I get your thoughts on this scenario:

Given this function call

colour_values(1:5, alpha = 1:5)

should the alpha values be

1. left as-is 1:5 (which, when converted to RRGGBBAA will be in the region of "00"), or
2. assumed to be a variable which needs to be scaled to 1:5 / 5 * 255 (so when converted will be "00","3F","7F","BF","FF" ?

from colourvalues.

I'd say 2. If you're scaling the values you should also scale the alpha vector.
But I'd also say alpha should be within [0,1].

Also, would someone actually want to specify a vector of alpha? The most common scenarios in my opinion are:

1. a constant alpha over all values
2. a special alpha for special values (i.e. NAs)
3. mapping of alpha to a (second) variable (in which case the UI usually accepts the name of a df column).

For 3. it should then be scaled to the same as the values vector.

from colourvalues.

I'm inclined to agree, and I think this point is key

mapping of alpha to a (second) variable (in which case the UI usually accepts the name of a df column).

With regards to

But I'd also say alpha should be within [0,1].

If we're scaling a column/vector of data then I don't think it matters the range of the values, as they have to be in [0,255] to be converted to #RRGGBBAA

from colourvalues.

If we're scaling a column/vector of data then I don't think it matters the range of the values, as they have to be in [0,255] to be converted to #RRGGBBAA

Agreed!

from colourvalues.

na.alpha as 0 or 255 by default?

from colourvalues.

although, it can be specified through na_colour

colour_values(c(1,2,NA,4,5), na_colour = "#80808000")
colour_values(c(1,2,NA,4,5), na_colour = "#808080FF")
colour_values(c(1,2,NA,4,5), na_colour = "#80808080")

from colourvalues.

I'd use the same default as alpha

from colourvalues.

Do you think a separate na.alpha is needed given it can be specified in na_colour ?

from colourvalues.

It depends, for leaflet e.g. the 8-digit hex notation was not respected (i.e. nothing was shown if in 8-digit hex) in some cases with the earlier (pre leafletjs 1.x). I am not sure how well 8-digit hex is supported in general (i.e. beyond web).

My approach in such cases is usually to not overload the api but wait and see if there is a need, so I would not implement it for now and highlight how to set it via na_colour.

Sorry for causing the stir and then recommend to not implement it... I had forgotten why we implemented a specific na.alpha in mapview.

from colourvalues.