Re: [9fans] Porter-Duff alpha blending

[andrey mirtchovski <mirtchovski@gmail.com>]

> Bug #3: MUL0123 is enabled whenever the src
> and dst both have 32-bit pixel width, but there is
> no check that the sub-channels are in the same
> order.  You don't say what the image chans were
> in your test, but this:
>
> src  rFF g00 b00 αFF
> mask  kFF αFF
> dst  r00 g00 b00 αFF
> dst after calc  rFE gFE b00 α00
>
> would be explained by, say, src==ARGB and
> dst==RGBA.  The A and R values in src became
> the R and G chans in dst.  (In fact, since the dst
> R and G are FE not FF, that's almost certainly
> the scenario, modulo the little-endian draw names.)

it was indeed ARGB/RGBA (or the other way around) as I had focused
testing only on those two.

thanks for the explanation!