fill transform breaks legend color accuracy

[mrjones-plip]

update: while filed as a but, this has since been moved to an enhancement. See comments below.

when you have map.countries.attr.fill.transform() method declared, the legend ends up being the wrong color compared to color the country is filled with.

steps to reproduce:

1. go to https://bl.ocks.org/melalj/07be61a538509b8e4a7e where map.countries.attr.fill.transform() is defined as:

   transform: function(val) {
       if (val === 0) return 0;
       return Math.sqrt(val);
   },
   

2. zoom in to Australia so it is behind the legend

3. hover over Australia so it's value is displayed on the legend

expected: legend color matches country color
actual: country color is much darker than legend color
workarounds: don't declare a transform() :(

[mrjones-plip]

here's the screenshot from step #3 above. you can see that the legend color of 222 does not match the country color:

[melalj]

@Ths2-9Y-LqJt6
The legend supports only a linear scale.
On the transform attribute, it transforms values with a square-root.
We should create a separate ticket to request this feature

[mrjones-plip]

@melalj - makes sense! I'll just convert this from a bug to a feature request.

[mrjones-plip]

if we implement PCH's IXP Dirs (https://pch.net/ixp) two functions (generateRanksFromMultipleRows() and getPercentile()) we could know how to properly render the legend

[melalj]

@Ths2-9Y-LqJt6 this might be fixed with the new aggregate function, can you QA?