[Buildroot] [PATCH 4/4] webkitgtk: explicitly set USE_GSTREAMER_GL build option

[Adrian Perez de Castro <aperez@igalia.com>]

Hi everybody,

I have some comments more about this topic, please read below...

On Thu, 11 Oct 2018 23:56:36 +0200, Arnout Vandecappelle <arnout@mind.be> wrote:
> 
> 
> On 11/10/18 21:23, Yann E. MORIN wrote:
> > Peter, Arnout, All,
> > 
> > On 2018-10-11 20:16 +0200, Peter Korsgaard spake thusly:
> >>>>>>> "Arnout" == Arnout Vandecappelle <arnout@mind.be> writes:
> >>  >  'imply' is syntactic sugar for 'default y if ...'. The *only* thing it changes
> >>  > is the place where you put the imply. (To be exact, it is the same as 'default
> >>  > ...' because it propagates the m/y/n state to the default, not just y/n. But
> >>  > since we don't use m, it doesn't matter.)
> >>
> >>  >  For this specific case, it is pretty obvious that putting a 'default y if
> >>  > BR2_PACKAGE_WEBKITGTK_MULTIMEDIA' on BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL
> > 
> > As the submitter said "in general it is preferred due to better
> > performance", why don't we just have, in webkitgtk:
> > 
> >     select BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL if BR2_PACKAGE_GST1_PLUGINS_BAD
> > 
> > Or even further:
> > 
> >     select BR2_PACKAGE_GST1_PLUGINS_BAD
> >     select BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL
> > 
> > Of course, that requires propagating the required dependencies...
> > But since webkitgtk already depends on libgtk3, which itself depends on
> > LIBEGL_WAYLAND or LIBGL, we're not too far off...
> 
>  For this specific case, that's a very good idea indeed. Something like (to be
> tested!):

While something like this would probably work, there can be cases in which
GStreamer-GL cannot be built (for example when there is no windowing system
supported by GStreamer-GL), but WebKitGTK+ may still build and work fine with
GL support enabled and GStreamer-GL support disabled. The GL code in WebKit
has a few different methods used at runtime as fall-back to create the GL
context [1].  On the other hand GStreamer-GL has a few more requirements on
the GL implementation than WebKit for building [2] ? so I do see value in
allowing to build without GStreamer-GL ?\_(?)_/? 

> config BR2_PACKAGE_WEBKITGTK_MULTIMEDIA
>         bool "multimedia support"
>         select BR2_PACKAGE_GSTREAMER1
>         select BR2_PACKAGE_GST1_PLUGINS_BAD
>         select BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL if
> BR2_PACKAGE_GST1_PLUGINS_BASE_HAS_LIB_OPENGL
>         ...
> 
>  Ideally we would also select the plugins that make sure HAS_LIB_OPENGL becomes
> true, but unfortunately that's really complicated. Selecting
> BR2_PACKAGE_GST1_PLUGINS_BASE_LIB_OPENGL would help, but that has the
> disadvantage that it might not actually make the GL plugin available (depending
> on the state of X11/wayland/...

I am a bit reluctant of doing this, due to the complications in making sure
that ?BR2_PACKAGE_GST1_PLUGINS_BASE_HAS_LIB_OPENGL? gets selected for all
configuration where it's supported, and the also complicated alternative of
using ?BR2_PACKAGE_GST1_PLUGINS_BASE_LIB_OPENGL?.

There's one more issue, though: I can't remember right now the precise case
(driver, GPU, GStreamer versions, etc), but some work mates from Igalia found
a couple of cases where using GStreamer-GL in WebKit results in garbled and/or
tinted video output, so it can actually be handy if we allow to manually
disable using it. So I'm leaning towards:

  if BR2_PACKAGE_WEBKITGTK_MULTIMEDIA

  config BR2_PACKAGE_WEBKITGTK_USE_GSTREAMER_GL
      bool "use gstreamer-gl"
	  default y
	  depends on BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL

  comment "using gstreamer-gl needs gst1-plugins-bad with the gl element enabled"
      depends on !BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_GL

  endif

WDYT?

> >>  > would be crazy. On the other hand, adding the imply in webkitgtk looks nice,
> >>  > concise and clear.
> > 
> > Sorry, I am still not convinced that using 'imply' in Buildroot is a
> > good idea overall... :-(
> > 
> >> Exactly, which is why I suggested it to Adrian.
> 
>  Apparently our BDFL disagrees :-)

I guess we will stay away from using ?imply? for now :)

Best regards,


-Adri?n


---
[1] In some cases it can even be enough that the driver supports Pbuffer
    contexts which with many drivers do not even require any windowing
	system running.
[2] Now that it's going to be Halloween, I could tell you some horror stories
    about how we have managed to run WebKit on some GL/EGL ?frankendriver?
	implementations :D
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