[PATCH wayland-web] FAQ: Modernise FAQ and inject some optimism
ppaalanen at gmail.com
Tue Jun 21 14:35:30 UTC 2016
On Tue, 21 Jun 2016 21:26:31 +1000
Daniel Stone <daniels at collabora.com> wrote:
> The FAQ was clearly written a very long time ago, when user sessions
> were a pipe dream, session compositors were the important thing, and we
> had a lot more questions than answers.
> Now things have solidified a bit, and I'm writing this from a native
> Wayland client inside a native Wayland-on-KMS desktop, rewrite good
> chunks of the FAQ to reflect today's reality a little better.
> Signed-off-by: Daniel Stone <daniels at collabora.com>
> faq.html | 115 ++++++++++++++++++++++++---------------------------------------
> 1 file changed, 43 insertions(+), 72 deletions(-)
> diff --git a/faq.html b/faq.html
> index 58b6fc9..edcd6df 100644
> --- a/faq.html
> +++ b/faq.html
> @@ -52,45 +52,30 @@
> behalf of the clients, it expects the clients to use whatever means
> they prefer to render into a shareable buffer. When the client is
> done, it informs the Wayland server of the new contents. The
> - current test clients use either cairo software rendering, cairo on
> - OpenGL or hardware accelerated OpenGL directly. As long as you have
> - a userspace driver library that will let you render into a sharable
> - buffer, you're good to go.
> + current test clients use either Cairo software rendering, Cairo on
> + OpenGL or hardware-accelerated OpenGL directly. Additionally, media
> + frameworks can share their buffers directly with the server. As
> + long as you have a userspace driver library that will let you render
> + into a shareable buffer, you're good to go.
> <h3>Is wayland replacing the X server?</h3>
> - It could replace X as the native Linux graphics server, but I'm sure
> - X will always be there on the side. I imagine that Wayland and X
> - will coexist in two ways on a Linux desktop: Wayland is a graphics
> - multiplexer for a number of X servers. Linux today typically only
> - uses one X server for GDM and the user session, but we'll probably
> - see that move to a dedicated GDM X server, an X server for user
> - sessions (spawning more on the fly as more users log in) and maybe a
> - dedicated screensaver/unlock X server. Right now we rely on VT
> - switching to move between X servers, and it's horrible. We have no
> - control over what the transitions look like and the VT ioctls are
> - pretty bad. Wayland provides a solution here, in that it can host
> - several X servers as they push their root window to Wayland as
> - surfaces. The compositor in this case will be a dedicated session
> - switcher that will cross-fade between X servers or spin them on a
> - cube.
> - Further down the road we run a user session natively under
> - Wayland with clients written for Wayland. There will still (always)
> - be X applications to run, but we now run these under a root-less X
> - server that is itself a client of the Wayland server. This will
> - inject the X windows into the Wayland session as native looking
> - clients. The session Wayland server can run as a nested Wayland
> - server under the system Wayland server described above, maybe even
> - side by side with X sessions. There's a number of intermediate
> - steps, such as running the GNOME screen saver as a native wayland
> - client, for example, or running a composited X desktop, where the
> - compositor is a Wayland client, pushing the composited desktop to
> - Wayland.
> + Mostly, yes. User sessions are able to run under Wayland today, via
> + a number of compositors: Weston itself as well as Enlightenment,
> + GNOME Shell, KDE, and a number of others under development. With
> + most toolkits having Wayland ports, as well as frameworks such as
> + GStreamer and SDL, it's perfectly possible to run a purely native
> + Wayland session as your desktop.
> + That being said, there are some clients which rely on X11, and
> + always will be. To that end, XWayland provides a plugin for Wayland
> + compositors, running a real X server. This gives legacy clients a
> + real and compliant X11 platform to run on, displayed side by side
> + with native Wayland clients in your Wayland session.
> <h3>Why not extend the X server?</h3>
> @@ -101,15 +86,11 @@
> exchange and update models that Wayland is built on into X.
> However, we have an option here of pushing X out of the hotpath
> between clients and the hardware and making it a compatibility
> - option. I'm not deluding myself that any general purpose desktop
> - Linux distribution will stop shipping X as we know it or as a
> - Wayland client anytime soon. Nor should they, there will still be X
> - applications to run and people expect that from a Linux desktop.
> - What's different now is that a lot of infrastructure has moved from
> - the X server into the kernel (memory management, command scheduling,
> - mode setting) or libraries (cairo, pixman, freetype, fontconfig,
> - pango, etc) and there is very little left that has to happen in a
> - central server process.
> + option. What's different now is that a lot of infrastructure has
> + moved from the X server into the kernel (memory management, command
> + scheduling, mode setting) or libraries (cairo, pixman, freetype,
> + fontconfig, pango, etc) and there is very little left that has to
> + happen in a central server process.
> <h3>What is wrong with X?</h3>
> @@ -129,25 +110,18 @@
> useful extensions. But we can't ever get rid of the core rendering
> API and much other complexity that is rarely used in a modern
> desktop. With Wayland we can move the X server and all its legacy
> - technology to an optional code path. Getting to a point where the X
> - server is a compatibility option instead of the core rendering
> - system will take a while, but we'll never get there if don't plan
> - for it.
> + technology to an optional code path.
> <h3>What about the overhead of running X on wayland?</h3>
> - If you're running a fullscreen X server, which pushes its root
> - window buffer to Wayland there is little overhead. If the X server
> - root window is transformed (i.e. scaled down or spinning on the side
> - of a cube) the Wayland compositor will have to do an extra copy to
> - get the pixels on screen. But once the animation finishes and the X
> - server buffer fills the entire screen, the Wayland compositor can
> - change the video scanout to source from the X server buffer and
> - retreat into the background. The X server uses the standard X.org
> - DDX drivers, renders directly to its pixmaps and its root window,
> - and the path from X to hardware is exactly as a native X.org server.
> + Most modern desktops already use an external compositing manager:
> + when the X server decides it needs to update content, it informs
> + this external process (usually your window manager), and allows it to
> + control the rendering entirely. Using XWayland is just the same as
> + this, but more efficient because the compositing manager doesn't have
> + to go back through the X server to display the content it rendered.
> <h3>Is Wayland network transparent / does it support remote rendering?</h3>
> @@ -210,21 +184,13 @@
> manager and compositor into one process. You can think of Wayland
> as a toolkit for creating clients and compositors. It is not a
> specific single compositor or window manager. If you want a
> - different window manager, you can write a new one.
> + different window manager, you can write a new one. A 'libweston'
> + effort is underway in order to allow new environments to reuse
> + Weston's codebase and mechanics, whilst providing their own look
> + and feel.
> - This may sound like a lot of work, but one of the key points about
> - Wayland is that the boilerplate code to a Wayland compositor is
> - comparable or less than the X boilerplate involved in becoming an X
> - window manager and compositor. Bringing up EGL and GLES2 on the
> - Linux KMS framebuffer and reading input from evdev can be done in
> - less than a thousand lines of code. The Wayland server side library
> - provides the protocol implementation and makes it easy to put the
> - pieces together.
up to this point, all looking really good.
> -<h3>Why does Wayland use EGL and GLES2?</h3>
> +<h3>Why does Wayland use EGL?</h3>
> EGL is the only GL binding API that lets us avoid dependencies on
> @@ -238,8 +204,13 @@
> A more subtle point is that libGL.so includes the GLX symbols, so
> linking to that library will pull in all the X dependencies. This
> means that we can't link to full GL without pulling in the client
> - side of X, so we're using GLES2 for now. Longer term, we'll need a
> - way to use full GL under Wayland.
> + side of X, so Weston uses OpenGL ES to render. This also enables
> + Weston to run on GPUs which don't support the full OpenGL API.
The above paragraph feels a bit out of place under the topic "Why does
Wayland use EGL?". It would feel more at home under a new question,
e.g. "Is Wayland limited to GL ES?". The last section of the
architecture page talks a lot about GLES2, too.
But, I wouldn't hold up landing this patch on that detail, so:
Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> + As detailed above, clients are however free to use whichever
> + rendering API they like.
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