17 lines
771 B
Python
17 lines
771 B
Python
def alpha_blend(src, dst):
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# Does not assume that dst is fully opaque
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# See https://en.wikipedia.org/wiki/Alpha_compositing - section on "Alpha Blending"
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src_multiplier = (src[3] / 255.0)
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dst_multiplier = (dst[3] / 255.0) * (1 - src_multiplier)
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result_alpha = src_multiplier + dst_multiplier
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if result_alpha == 0: # special case to prevent div by zero below
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return (0, 0, 0, 0)
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else:
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return (
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int(((src[0] * src_multiplier) + (dst[0] * dst_multiplier)) / result_alpha),
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int(((src[1] * src_multiplier) + (dst[1] * dst_multiplier)) / result_alpha),
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int(((src[2] * src_multiplier) + (dst[2] * dst_multiplier)) / result_alpha),
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int(result_alpha * 255)
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)
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