I need a function to return RGBA values based on a variable

Question

I have a variabble ranging from -10 to 10 and constantly changing. I want to have a python function returning RGBA values:

Red: when close to -10,
Green: when close to 10

I can't think of a way to do this myself and I suppose someone has done something like that in the past.

Answer 1

You can use a color representation like HSV to do this. You can take your rgb color max (255, 0, 0) and min (0, 255, 0) and convert those to HSV (0, 100%, 100%) (120, 100%, 100%). Looking at these you can see that only one value changes, the hue. So you can map your range -10:10 to the range of the hue 0:120. This can be done using a pretty simple mapping function:

def map_values(oldValue):
    # this is your range -10:10
    OldRange = (10 - -10)
    # range we are mapping to 0:120
    NewRange = (120 - 0)
    return (((oldValue - -10) * NewRange) / OldRange) + 0

Now that you have a hue, you can convert that into an RGB value. There is a handy function for this in colorsys

import colorsys
# we need to divide by 360 because this function
# expects a value from 0.0 to 1.0. H has a range from 0 to 360
my_rgb_color = colorsys.hsv_to_rgb(map_values(your_value) / 360.0, 1.0, 1.0)