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from __future__ import absolute_import, division, print_function
from matplotlib.colors import ColorConverter
__all__ = ['alpha_blend_colors']
COLOR_CONVERTER = ColorConverter()
def alpha_blend_colors(colors, additional_alpha=1.0):
"""
Given a sequence of colors, return the alpha blended color.
This assumes the last color is the one in front.
"""
srcr, srcg, srcb, srca = COLOR_CONVERTER.to_rgba(colors[0])
srca *= additional_alpha
for color in colors[1:]:
dstr, dstg, dstb, dsta = COLOR_CONVERTER.to_rgba(color)
dsta *= additional_alpha
outa = srca + dsta * (1 - srca)
outr = (srcr * srca + dstr * dsta * (1 - srca)) / outa
outg = (srcg * srca + dstg * dsta * (1 - srca)) / outa
outb = (srcb * srca + dstb * dsta * (1 - srca)) / outa
srca, srcr, srcg, srcb = outa, outr, outg, outb
return srcr, srcg, srcb, srca
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