Upcoming Qt switch to OpenGL ES on arm64

[Raphael Hertzog]

Hello,

On Sat, 24 Nov 2018, bret curtis wrote:
> Moving Qt back to using Desktop GL from GLES is going to have zero
> impact performance on the RPi since the VC4 supports up to OpenGL 2.1
> and and GLES 2.0 [1]

That's a different claim to what you made in a former message.

> The problem is that there are applications that make use of Qt that do
> not support GLES while Qt can support both. So these things can't be
> shipped on armel and armhf and now possibly arm64.
> 
> What applications does Debian have in its repo that only support GLES?

Wrong question. Maybe it makes sense for you at the application level for
the application that are hooking into OpenGL directly. But we are speaking
of having decent graphical performances for all Qt based-applications on
hardware that only support GLES and not Desktop OpenGL.

That kind of hardware does exist now and people who try to use Debian
on it will be disappointed because even LXQt will feel sluggish on them.

This is not a easy decision to make, in the ideal world we would support
both Qt stack but this is not realistic and we have to make a choice.

So basically there are two choices:

1/ 99% of users get decent performance with 98% of the Qt-based
   applications, but 2% of the applications will not work because
   they only support Qt with Desktop OpenGL or have some other
   incompatibility (2% is probably over-inflated, but the order
   is roughly correct and enough to get my point)

2/ 50% of the arm64 users have sluggish/unusable KDE/Qt-based applications
   and 50% of the users have the best performance with their Qt-based
   applications and those can also benefit from the 2% of the applications
   that would not be available otherwise. Those applications can be fixed
   to build with either OpenGL or GLES.
   (and here I'm saying 50% are losing but with the hardware available
   right now, it's certainly more than 50%... most arm64 boards are
   tailored for the embedded/mobile market)
   
In my opinion, Debian as a universal operating system should make choice
#1 so that most hardware bought by most users work well with most
applications. Getting 2% more applications or 20% more performance on the
applications at the cost of 50% of the users not being able to use their
hardware with decent performance is not the correct choice.

Cheers,

PS: None of the figures are accurate but I believe that they are not
misleading and are enough to understand my reasoning. For example,
I have no idea how much faster Qt with Desktop OpenGL vs Qt with GLES can
be.
-- 
Raphaël Hertzog ◈ Debian Developer

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