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---
root:
items:
- type: rect
bounds: [0, 0, 100, 100]
# First blend black rect with green in place
# Cs = (1 - αb) x Cs + αb x B(Cb, Cs)
# B(Cb, Cs) = | Cb - Cs | = (0, 0, 0)
# 0.5 * (0, 255, 0) + 0.5 * (0, 0, 0) = (0, 127.5, 0)
#
# Now, composite the resulting color with src-over; the alpha is the original alpha for the top layer
# while the color is the blending result
# co = αs x Fa x Cs + αb x Fb x Cb - this is premultiplied
# αo = αs + αb x (1 – αs)
# Source over: Fa = 1; Fb = 1 – αs
# co = 0.5 * 1 * (0, 127.5, 0) + 0.5 * 0.5 * (0, 255, 0) = (0, 63.5, 0) + 0.25 * (0, 255, 0) = (0, 127.5, 0)
# ao = 0.5 + 0.5 * 0.5 = 0.75
# Co = co/ao = (0, 127.5, 0) / 0.75
#
# Now alpha composite on white background
# co = 0.75 * 1 * (0, 127.5, 0) / 0.75 + 1 * 0.25 * (255, 255, 255) = (0, 127.5, 0) + (63.75, 63.75, 63.75) = (63.75, 159, 63.75) = (64, 191, 64)
color: [64, 191, 64]
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