[Qemu-devel] Re: [PATCH] sdl.c: support 32 bpp cursors

[Reimar Döffinger]

On Mon, Aug 17, 2009 at 06:48:09PM +0200, Paolo Bonzini wrote:
> On 08/17/2009 05:58 PM, Reimar Döffinger wrote:
> > The thing I am unsure about though is which byte is the unused one and
> > should be skipped, the first or the last - for the black-and-white
> > cursors I tested it doesn't make a difference...
> 
> You could skip the one that is always zero.  If none is, then one of the 
> bytes is the alpha and you should either skip no byte, or set src _just 
> to that_ byte.

There is no alpha, there is already a mask that defines transparency,
the 4th byte is only padding and should be ignored, just like for the
framebuffer (where that issue even made it into the FAQ since some
library incorrectly treated that as alpha which gave strange effects).
Well, at least that's how I am convinced it should be, I have not yet
found a specification or even proper documentation for this stuff (I
admit I haven't looked too hard).