[RFC 0/2] Add fp16 formats

Pekka Paalanen ppaalanen at gmail.com
Wed Feb 6 08:09:01 UTC 2019

On Tue, 5 Feb 2019 21:57:40 +0000
"Strasser, Kevin" <kevin.strasser at intel.com> wrote:

> Pekka Paalanen wrote:
> > On Mon, 4 Feb 2019 22:10:00 +0000 "Strasser, Kevin"
> > <kevin.strasser at intel.com> wrote:  
> > > That is what I was trying to achieve, offering applications fp16 scan
> > > out buffers. I'm not aware of any explicit requirement for adding the
> > > wl_shm format outside of Mesa's Walyand egl driver, which includes
> > > WL_SHM_FORMAT* for each supported visual (I think just for the swrast path).  
> >
> > That should really be only the software rendering paths and they use wl_shm
> > specifically.
> >
> > The hardware rendering paths should use DRM formats (drm_fourcc), everything
> > is kind of standardising around those these days.  
> Ok, I *think* we are on the same page. Once the drm formats have landed in the
> kernel we will add the equivalent to wl_shm (probably my first patch unless we
> decide on some other fourcc definition). This will make fp16 visuals available
> for hardware and software (swrast) paths in the egl driver. That should cover
> the requirements for use in Weston's gl renderer.


let me be more specific just in case. :-)

The wl_shm format patch is only necessary if you want to have fp16
buffer format with software rendering. This is because the software
rendering glue uses wl_shm Wayland buffers to send the content to a
Wayland compositor.

If you are happy to limit fp16 to hardware rendering on Wayland, you do
not need to think of wl_shm at all. Hardware rendering uses
zwp_linux_dmabuf (or the old wl_drm) Wayland buffers, which simply say
"use the kernel DRM format definitions".

Defining the formats is only for a common vocabulary. The formats a
Wayland compositor will actually support are advertised explicitly at
runtime, which I believe should affect things like what EGLConfigs an
app sees available.

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