Proof of concept patch for Wash Mode artifacts

[Lukast dev]

Hi Dmitry,

can you check if this fixes also this bug?
https://bugs.kde.org/show_bug.cgi?id=300665

Lukas

2013/6/16 Dmitry Kazakov <dimula73 at gmail.com>:
> Hi!
>
> One of the bugs I'm working on currently is Wash Mode bug, described by Paul
> in the first part of the bug [0].
>
> Technical part:
>
> Actually, this is not a bug, but a flaw of the composition formula we use in
> ALPHA_DARKEN composite op. So to fix this bug, we need to change the formula
> (with all the obvious consequences). The problem is this formula is not
> commutative, that is the order of application of dabs changes the result
> dramatically.
>
> The patch:
>
> In the attachment you can find a patch which (should) fix this bug. It would
> be nice if someone tested it and looked for some non-obvious regressions in
> painting it introduces.
>
> This patch implements:
> 1) Fixes the artifacts on the tail of the Wash Mode stroke
>
> This patch breaks (known issues):
> 1) Flow option doesn't work (it is simply disabled)
> 2) It fixes the bug for a Pixel Brush only
> 3) It disables vector optimizations
>
>
> [0] - https://bugs.kde.org/show_bug.cgi?id=320651
>
> --
> Dmitry Kazakov
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