Review Request 108709: in KisPlainColorSource equally distribute mix factor between values [0..255]

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This review has been submitted with commit 780fe134176171a032b58c75cb7d6614aa42613d by Friedrich W. H. Kossebau to branch master.

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On Feb. 3, 2013, 1:12 a.m., Friedrich W. H. Kossebau wrote:
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> http://git.reviewboard.kde.org/r/108709/
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> (Updated Feb. 3, 2013, 1:12 a.m.)
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> Review request for Calligra, Cyrille Berger Skott and Boudewijn Rempt.
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> Description
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> While I just wanted to fix the warning about "(qint16)255 - weight" possibly being out-of-range, I wondered if the calculation of the parts of the colors being mixed in is behaving like wanted.
> The old code "(int)(mix * 255)" will map to "0" for values of mix in the range of [0..1/255[, while it will only map to 255 when mix is exactly 1.0.
> Which gives the foreground color less power than the background color in average here.
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> Attached patch fixes that by using the formula "int(mix * 256)" which distributes the values [0.0..1.0[ equally to the range [0..255], with the exception of 1.0, which would be 256, but that can be catched.
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> The proposed algorithm might be more correct, but has the problem that any stored settings of the mix value would result in slight color changes. No idea if that can happen, your call.
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> Any better algorithm?
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> If okay, okay to also backport to 2.6?
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> Diffs
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>   krita/plugins/paintops/libpaintop/kis_color_source.cpp fe19834 
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> Diff: http://git.reviewboard.kde.org/r/108709/diff/
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> Testing
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> Thanks,
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> Friedrich W. H. Kossebau
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