[Qemu-devel] Very small VGA window sizes (was: Re: [PATCH 0/6] Add GTK UI to enable basic accessibility)

[Stefan Weil <sw@weilnetz.de>]

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Am 25.02.2012 22:15, schrieb Stefan Weil:
> Am 25.02.2012 21:11, schrieb Anthony Liguori:
>> On 02/25/2012 11:02 AM, Stefan Weil wrote:
>>> Am 20.02.2012 00:44, schrieb Anthony Liguori:
>>>> Hi,
>>>>
>>>> I realize UIs are the third rail of QEMU development, but over the 
>>>> years I've
>>>> gotten a lot of feedback from users about our UI. I think everyone 
>>>> struggles
>>>> with the SDL interface and its lack of discoverability but it's 
>>>> worse than I
>>>> think most people realize for users that rely on accessibility tools.
>>>>
>>>> The two pieces of feedback I've gotten the most re: accessibility 
>>>> are the lack
>>>> of QEMU's enablement for screen readers and the lack of configurable
>>>> accelerators.
>>>>
>>>> Since we render our own terminal using a fixed sized font, we don't 
>>>> respect
>>>> system font settings which means we ignore if the user has 
>>>> configured large
>>>> print.
>>>>
>>>> We also don't integrate at all with screen readers which means that 
>>>> for blind
>>>> users, the virtual consoles may as well not even exist.
>>>>
>>>> We also don't allow any type of configuration of accelerators. For 
>>>> users with
>>>> limited dexterity (this is actually more common than you would 
>>>> think), they may
>>>> use an input device that only inputs one key at a time. Holding 
>>>> down two keys
>>>> at once is not possible for these users.
>>>>
>>>> These are solved problems though and while we could reinvent all of 
>>>> this
>>>> ourselves with SDL, we would be crazy if we did. Modern toolkits, 
>>>> like GTK,
>>>> solve these problems.
>>>>
>>>> By using GTK, we can leverage VteTerminal for screen reader 
>>>> integration and font
>>>> configuration. We can also use GTK's accelerator support to make 
>>>> accelerators
>>>> configurable (Gnome provides a global accelerator configuration 
>>>> interface).
>>>>
>>>> I'm not attempting to make a pretty desktop virtualization UI. 
>>>> Maybe we'll go
>>>> there eventually but that's not what this series is about.
>>>>
>>>> This is just attempting to use a richer toolkit such that we can 
>>>> enable basic
>>>> accessibility support. As a consequence, the UI is much more usable 
>>>> even for a
>>>> user without accessibility requirements so it's a win-win.
>>>
>>> This first version of the new GTK UI still shares some problems with
>>> the SDL UI and adds new ones:
>>>
>>> It's quite common for the VGA code to set a very small size (e.g. 1 
>>> x 1 pixel)
>>> during boot. MIPS Malta does (if no VGA module like cirrusfb is loaded,
>>> it will never set a different size), and even the 386 / x86_64 
>>> emulation
>>> has a (very short) time were the display size is unusually small.
>>
>> It doesn't.  It cycles through modes 640x480, 720x400, then VGA 
>> modes.  It never resizes to 1x1.
>>
>> But..  GTK should handle this better.  Even if the drawing area sets 
>> the size to 1x1, the window should maintain a size at least large 
>> enough to render the menu bar properly. ss/ssssssssssssss/
>
> Just run QEMU on a sufficiently slow host, for example QEMU in QEMU,
> or slow down the execution of QEMU by other means, then you will see
> which window sizes are then selected. Maybe you also need -singlestep.
> You _will_ get a very small window!
>
> I just got it using this call on a netbook running Ubuntu:
>
> qemu-system-i386 -L pc-bios -singlestep -d in_asm,out_asm
>
> Don't use KVM, of course - we want to slow down QEMU!
> Adding strace is also a good way to reduce execution speed.
>
> Cheers,
>
> Stefan Weil


This also works to get the small window:

gdb --args i386-softmmu/qemu-system-i386 -L pc-bios -singlestep

Set a breakpoint on gd_resize and run. Here is the result (2nd hit of
the breakpoint):

Breakpoint 2, gd_resize (ds=0x809f7c40) at 
/home/stefan/src/qemu/qemu.org/qemu/ui/gtk.c:182
182        GtkDisplayState *s = ds->opaque;
2: ds->surface->width = 9
1: ds->surface->height = 1

So the new window is 9 x 1 pixels.

Regards,
Stefan Weil


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