Xgl introduces a new pixel format that's a 32 bit depth with a true 
alpha channel.  When we let SDL choose a depth on an Xgl server, it 
picks up this format (as it's the native pixel format in Xgl).  We don't 
fill out the alpha channel which results in a completely transparent screen.

This patch fills out the alpha channel to all 1s for 32 bit pixels.  I'm 
not sure if this handles every case where a pixel is generated but it 
seems to work on all of my VMs.  I really don't like this patch as it 
seems like a hack but I couldn't figure out a way to differentiate in 
SDL between a 24-bit depth with a 32-bit pixel width (which is a common, 
non-alpha format) and a true 32 bit depth with an alpha channel.

Hopefully, this will be fixed in future versions of SDL.

Regards,

Anthony Liguori