Get values from transform

How can I get the values of data that is specified via a transform?

Let’s say I have a glyph with ‘xs’:{‘field’:‘xs’}

Somewhere in the algorithm the actual data value NEED to be fetched, could I get a link to the code that syntax triggers?

How do I get the array of values that ‘xs’ refers to?

For example if you have a LinearColorMapper. And you plot a matrix with rect()

You can specify the fill_color with

fill_color ={‘field’:‘somefield’,‘transform’:mapper}


How can I access the actual values of fill_color?