Remote display with 3D acceleration using Wayland/Weston

[DRC]

On 12/15/16 3:01 AM, Pekka Paalanen wrote:
> The current RDP-backed is written to set up and use only the Pixman
> renderer. Pixman renderer is a software renderer, and will not
> initialize EGL in the compositor. Therefore no support for hardware
> accelerated OpenGL gets advertised to clients, and clients fall back to
> software GL.
> 
> You can fix this purely by modifying libweston/compositor-rdp.c file,
> writing the support for initializing the GL-renderer. Then you get
> hardware accelerated GL support for all Wayland clients without any
> other modifications anywhere.
> 
> Why that has not been done already is because it was thought that
> having clients using hardware OpenGL while the compositor is not cannot
> be performant enough to justify the effort. Also, it pulls in the
> dependency to EGL and GL libs, which are huge. Obviously your use case
> is different and this rationale does not apply.
> 
> The hardest part in adding the support to the RDP-backend is
> implementing the buffer content access efficiently. RDP requires pixel
> data in system memory so the CPU can read it, but GL-renderer has all
> pixel data in graphics memory which often cannot be directly read by
> the CPU. Accessing that pixel data requires a copy (glReadPixels), and
> there is nowadays a helper: weston_surface_copy_content(), however the
> function is not efficient and is so far meant only for debugging and
> testing.

I am attempting to modify the RDP backend to prove the concept that
hardware-accelerated OpenGL is possible with a remote display backend,
but my lack of familiarity with the code is making this very
challenging.  It seems that the RDP backend uses Pixman both for GL
rendering and also to maintain its framebuffer in main memory
(shadow_surface.)  Is that correct?  If so, then it seems that I would
need to continue using the shadow surface but use gl_renderer instead of
the Pixman renderer, then implement my own method of transferring pixels
from the GL renderer to the shadow surface at the end of every frame (?)
 I've been trying to work from compositor-wayland.c as a template, but
it's unclear how everything connects, which parts of that code I need in
order to implement hardware acceleration, and which parts are
unnecessary.  I would appreciate it if someone who has familiarity with
the RDP backend could give me some targeted advice.