[Pixman] [PATCH] sse2: Skip src pixels that are zero in sse2_composite_over_8888_n_8888()

Jonathan Morton jonathan.morton at movial.com
Thu Dec 23 08:27:05 PST 2010

On Thu, 2010-12-23 at 17:05 +0100, Krzysztof Kosiński wrote:
> > This patch doesn't handle cases where alpha is zero but components
> are not.  Not sure if this is either possible or frequent.
> Pixman uses premultiplied alpha so such values are not possible.

No, they are possible, and they have defined effects.  Essentially, this
turns the colour part into an additive.  But no, it is not very
frequently used.

In any case, it looks to me as though the code correctly tests the
entire 32-bit pixel against zero, so this case is already taken into

From: Jonathan Morton
      jonathan.morton at movial.com

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