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

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

[Michael Tokarev]

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.

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

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
>