Re: [Qemu-devel] [PATCH] ui/egl-helpers: fix egl 1.5 display init

[Frediano Ziglio <fziglio@redhat.com>]

> 
> On 03/17/2017 05:53 AM, Marc-André Lureau wrote:
> > On Fri, Mar 17, 2017 at 12:12 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
> >
> >> Unfortunaly switching to getPlatformDisplayEXT isn't as easy as
> >> implemented by 0ea1523fb6703aa0dcd65e66b59e96fec028e60a.  See the
> >> longish comment for the complete story.
> >>
> >> Cc: Frediano Ziglio <fziglio@redhat.com>
> >> Suggested-by: Hans de Goede <hdegoede@redhat.com>
> >> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> >> ---
> >
> >
> >
> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> 
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> 
> >>  ui/egl-helpers.c | 53
> >> +++++++++++++++++++++++++++++++++++++++++++++++------
> >>  1 file changed, 47 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/ui/egl-helpers.c b/ui/egl-helpers.c
> >> index 584dd1b..48686cf 100644
> >> --- a/ui/egl-helpers.c
> >> +++ b/ui/egl-helpers.c
> >> @@ -192,6 +192,51 @@ EGLSurface qemu_egl_init_surface_x11(EGLContext ectx,
> >> Window win)
> >>
> >>  /* ----------------------------------------------------------------------
> >> */
> >>
> >> +/*
> >> + * Taken from glamor_egl.h from the Xorg xserver, which is MIT licensed
> >> + *
> >> + * Create an EGLDisplay from a native display type. This is a little
> >> quirky
> >> + * for a few reasons.
> >> + *
> >> + * 1: GetPlatformDisplayEXT and GetPlatformDisplay are the API you want
> >> to
> >> + * use, but have different function signatures in the third argument;
> >> this
> >> + * happens not to matter for us, at the moment, but it means epoxy won't
> >> alias
> >> + * them together.
> >> + *
> >> + * 2: epoxy 1.3 and earlier don't understand EGL client extensions, which
> >> + * means you can't call "eglGetPlatformDisplayEXT" directly, as the
> >> resolver
> >> + * will crash.
> >> + *
> >> + * 3: You can't tell whether you have EGL 1.5 at this point, because
> >> + * eglQueryString(EGL_VERSION) is a property of the display, which we
> >> don't
> >> + * have yet. So you have to query for extensions no matter what.
> >> Fortunately
> >> + * epoxy_has_egl_extension _does_ let you query for client extensions, so
> >> + * we don't have to write our own extension string parsing.
> >> + *
> >> + * 4. There is no EGL_KHR_platform_base to complement the EXT one, thus
> >> one
> >> + * needs to know EGL 1.5 is supported in order to use the
> >> eglGetPlatformDisplay
> >> + * function pointer.
> >> + * We can workaround this (circular dependency) by probing for the EGL
> >> 1.5
> >> + * platform extensions (EGL_KHR_platform_gbm and friends) yet it doesn't
> >> seem
> >> + * like mesa will be able to adverise these (even though it can do EGL
> >> 1.5).
> >> + */
> >> +static EGLDisplay qemu_egl_get_display(void *native)
> >> +{
> >> +#ifdef EGL_PLATFORM_GBM_MESA
> >> +    /* In practise any EGL 1.5 implementation would support the EXT
> >> extension */
> >> +    if (epoxy_has_egl_extension(NULL, "EGL_EXT_platform_base")) {

Should not check EGL_MESA_platform_gbm instead?
What happens if package is compiled against Mesa but in the system Nvidia
OpenGL is installed? In this case EGL_PLATFORM_GBM_MESA is defines,
possibly EGL_EXT_platform_base is supported but EGL_PLATFORM_GBM_MESA
is not as Nvidia does not support it (so EGL_PLATFORM_GBM_MESA won't work).

Maybe Xorg code support also Nvidia case (that does not have gbm) ?

> >> +        PFNEGLGETPLATFORMDISPLAYEXTPROC getPlatformDisplayEXT =
> >> +            (void *) eglGetProcAddress("eglGetPlatformDisplayEXT");
> >> +        if (getPlatformDisplayEXT) {
> >> +            return getPlatformDisplayEXT(EGL_PLATFORM_GBM_MESA, native,
> >> NULL);
> >> +        }
> >> +    }
> >> +#endif
> >> +
> >> +    /* fallback */
> >> +    return eglGetDisplay(native);
> >> +}
> >> +
> >>  int qemu_egl_init_dpy(EGLNativeDisplayType dpy, bool gles, bool debug)
> >>  {
> >>      static const EGLint conf_att_gl[] = {
> >> @@ -222,12 +267,8 @@ int qemu_egl_init_dpy(EGLNativeDisplayType dpy, bool
> >> gles, bool debug)
> >>          setenv("LIBGL_DEBUG", "verbose", true);
> >>      }
> >>
> >> -    egl_dbg("eglGetDisplay (dpy %p) ...\n", dpy);
> >> -#ifdef EGL_MESA_platform_gbm
> >> -    qemu_egl_display = eglGetPlatformDisplayEXT(EGL_PLATFORM_GBM_MESA,
> >> dpy, NULL);
> >> -#else
> >> -    qemu_egl_display = eglGetDisplay(dpy);
> >> -#endif
> >> +    egl_dbg("qemu_egl_get_display (dpy %p) ...\n", dpy);
> >> +    qemu_egl_display = qemu_egl_get_display(dpy);
> >>      if (qemu_egl_display == EGL_NO_DISPLAY) {
> >>          error_report("egl: eglGetDisplay failed");
> >>          return -1;