[Mesa-dev] [PATCH V2] Check if the window is non-NULL before setting swap interval.

[Eric Engestrom]

On Thursday, 2018-08-30 17:55:14 +0900, Tomasz Figa wrote:
> Hi Erik, Emil, Eric,
> 
> On Tue, Jul 10, 2018 at 12:41 AM Erik Faye-Lund <kusmabite at gmail.com> wrote:
> >
> > On Thu, Jul 5, 2018 at 7:02 PM Emil Velikov <emil.l.velikov at gmail.com> wrote:
> > >
> > > On 5 July 2018 at 17:17, Eric Engestrom <eric.engestrom at intel.com> wrote:
> > > > On Thursday, 2018-07-05 14:43:02 +0100, Emil Velikov wrote:
> > > >> On 5 July 2018 at 10:53, Eric Engestrom <eric.engestrom at intel.com> wrote:
> > > >> > On Monday, 2018-07-02 14:12:44 +0530, samiuddi wrote:
> > > >> >> This fixes crash due to NULL window when swap interval is set
> > > >> >> for pbuffer surface.
> > > >> >>
> > > >> >> Test: CtsDisplayTestCases pass
> > > >> >>
> > > >> >> Signed-off-by: samiuddi <sami.uddin.mohammad at intel.com>
> > > >> >> ---
> > > >> >>
> > > >> >> Kindly ignore this patch
> > > >> >> https://lists.freedesktop.org/archives/mesa-dev/2018-July/199098.html
> > > >> >>
> > > >> >>  src/egl/drivers/dri2/platform_android.c | 2 +-
> > > >> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >> >>
> > > >> >> diff --git a/src/egl/drivers/dri2/platform_android.c b/src/egl/drivers/dri2/platform_android.c
> > > >> >> index ca8708a..b5b960a 100644
> > > >> >> --- a/src/egl/drivers/dri2/platform_android.c
> > > >> >> +++ b/src/egl/drivers/dri2/platform_android.c
> > > >> >> @@ -485,7 +485,7 @@ droid_swap_interval(_EGLDriver *drv, _EGLDisplay *dpy,
> > > >> >>     struct dri2_egl_surface *dri2_surf = dri2_egl_surface(surf);
> > > >> >>     struct ANativeWindow *window = dri2_surf->window;
> > > >> >>
> > > >> >> -   if (window->setSwapInterval(window, interval))
> > > >> >> +   if (window && window->setSwapInterval(window, interval))
> > > >> >>        return EGL_FALSE;
> > > >> >
> > > >> > Shouldn't we return false if we couldn't set the swap interval?
> > > >> >
> > > >> > I think this should be:
> > > >> >    if (!window || window->setSwapInterval(window, interval))
> > > >> >       return EGL_FALSE;
> > > >> >
> > > >> Changing the patch as above will lead to eglSwapInterval consistently
> > > >> failing for pbuffer surfaces.
> > > >
> > > > I'm not that familiar with pbuffers, but does SwapInterval really make
> > > > sense for them? I thought you couldn't swap a pbuffer.
> > > >
> > > > If so, failing an invalid op seems like the right thing to do.
> > > > Otherwise, I guess sure, no-op returning success is fine.
> > > >
> > > Looking at eglSwapInterval manpage [1] (with my annotation):
> > > "eglSwapInterval — specifies the minimum number of video frame periods
> > > per buffer swap for the _window_ associated with the current context."
> > > While the spec does not mention window/pbuffer/pixmap at all - it
> > > extensively refers to eglSwapBuffers.
> > >
> > > Wrt eglSwapBuffers manpage [2] and spec are consistent:
> > >
> > > "If surface is a pixel buffer or a pixmap, eglSwapBuffers has no
> > > effect, and no error is generated."
> > >
> > > Perhaps it's wrong to set eglSwapInterval for !window surfaces, but
> > > its sibling (eglSwapBuffers) does not error out.
> > > Hence I doubt many users make a distinction between window and pbuffer
> > > surfaces for eglSwap*.
> > >
> > > Worth bringing to the WG meeting - it' planned for 1st August.
> > >
> >
> > As I pointed out when I proposed this variant here:
> > https://patchwork.freedesktop.org/patch/219313/
> >
> > "Also, I don't think EGL_FALSE is the right return-value, as it doesn't
> > seem the EGL 1.5 spec defines any such error. Also, for instance
> > dri2_swap_interval returns EGL_TRUE when there's no driver-function,
> > which further backs the "silent failure" in this case IMO."
> >
> > So I think EGL_TRUE is the correct return-value for now. If the spec
> > gets changed, we can of course update our implementation.
> 
> What happens to this patch in the end? It looks like we're observing a
> similar problem in Chrome OS.
> 
> Emil, was there any follow-up on the WG meeting?

Meeting was cancelled, but I raised the issue here:
https://gitlab.khronos.org/egl/API/merge_requests/17

Right now we have ARM saying they return false + error and NVIDIA saying
they return true + no error and that ARM has a bug.
I think another party adding their opinion might nudge it forward :)

> 
> Best regards,
> Tomasz