Re: Corrupted display changing screen colour depth in qemu-system-ppc/MacOS

[Mark Cave-Ayland]

On 22/07/2022 14:44, Marc-André Lureau wrote:

> Hi
>
> On Fri, Jul 22, 2022 at 4:28 PM Howard Spoelstra <hsp.cat7@gmail.com> wrote:
> > On Fri, Jun 17, 2022 at 2:38 PM Marc-André Lureau <marcandre.lureau@redhat.com> 
> > wrote:
> > > Hi
> > >
> > > On Fri, Jun 17, 2022 at 1:56 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
> > > >    Hi,
> > > >
> > > > > > Can you try ditch the QEMU_ALLOCATED_FLAG check added by the commit?
> > > > >
> > > > > Commit cb8962c146 drops the QEMU_ALLOCATED_FLAG check: if I add it back in
> > > > > with the following diff on top then everything works again:
> > > >
> > > > Ah, the other way around.
> > > >
> > > > > diff --git a/ui/console.c b/ui/console.c
> > > > > index 365a2c14b8..decae4287f 100644
> > > > > --- a/ui/console.c
> > > > > +++ b/ui/console.c
> > > > > @@ -2400,11 +2400,12 @@ static void vc_chr_open(Chardev *chr,
> > > > >
> > > > >   void qemu_console_resize(QemuConsole *s, int width, int height)
> > > > >   {
> > > > > -    DisplaySurface *surface;
> > > > > +    DisplaySurface *surface = qemu_console_surface(s);
> > > > >
> > > > >       assert(s->console_type == GRAPHIC_CONSOLE);
> > > > >
> > > > > -    if (qemu_console_get_width(s, -1) == width &&
> > > > > +    if (surface && (surface->flags & QEMU_ALLOCATED_FLAG) &&
> > > > > +        qemu_console_get_width(s, -1) == width &&
> > > > >           qemu_console_get_height(s, -1) == height) {
> > > > >           return;
> > > > >       }
> > > > >
> > > > > > Which depth changes triggers this?  Going from direct color to a
> > > > > > paletted mode?
> > > > >
> > > > > A quick test suggests anything that isn't 32-bit colour is affected.
> > > >
> > > > Hmm, I think the commit should simply be reverted.
> > > >
> > > > Short-cutting the qemu_console_resize() call is only valid in case the
> > > > current surface was created by qemu_console_resize() too.  When it is
> > > > something else -- typically a surface backed by vga vram -- it's not.
> > > > Looking at the QEMU_ALLOCATED_FLAG checks exactly that ...
> > >
> > > Oh ok, it might be worth adding a comment to clarify that. By
> > > reverting, we are going back to the situation where
> > > qemu_console_resize() will create a needless surface when rendering
> > > with GL. As I tried to explain in the commit message, it will need
> > > more changes to prevent that. I can take a look later.
> >
> > Hi Marc-André,
> >
> > I wondered whether you've had a chance to look at this?
>
> No, it's not clear to me how to reproduce it. Someone that can
> actually test it should send a patch with some comments to explain it.

Unfortunately I don't know anything about the host display code, but I think I should 
be able to come up with some Forth to run from the command line that will reproduce 
the issue with qemu-system-ppc. Let me see if I can come up with something...


ATB,

Mark.