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