Re: [Qemu-devel] SDL fullscreen window dislikes being resized past the screen size

[Anthony Liguori]

On 05/25/2010 10:53 AM, Michael Tokarev wrote:
> Initially it were a bugreport on #kvm IRC, someone
> asked why his kvm exits when entering fullscreen mode,
> saying the famous
>  "Could not open SDL display"
> and nothing more.
>
> I added a bit of debug output and here's what I see:
>
> ...
> resizing to 1440x900 0 0x115
> resizing to 1440x900 32 0x80000115
> Could not open SDL display for 1440x900, bpp=32, flags=0x80000115
>
> flag=0x80000000 means fullscreen.  My screen size is
> 1280x1024, -- 1440 is more than 1280.
>
> It works just fine if I choose resolution less or equal
> to my screen size.

Depending on how SDL is configured, it uses DGA or some other relic to 
actually implement full screen mode.  You cannot get a DGA screen that's 
larger than the physical monitor since it's often backed by video 
memory.  SDL isn't smart enough to degrade into a scaled mode either.

Honestly, SDL full screen mode is a bad idea.  We offer no indication 
that the guest is actually running which is potentially very 
confusing/dangerous.  We need a better backend to really implement a 
functioning full screen mode.

Regards,

Anthony Liguori

> And it works just fine (as seen in the example output
> above) that it works with larger resolutions but not
> fullscreen (in that case SDL window will be scaled to
> fit the actual desktop size).
>
> It looks to me like an incorrect usage or assumptions
> about SDL window, or maybe SDL bug.  Mine is
> libsdl1.2debian 1.2.13-2.
>
> And the error message is in usual qemu style - not at
> all useful :)  But it's at least better than pure
> exit without any messages at all, like was in hugetlbfs
> code ;)
>
> Thanks!
>
> /mjt