Den 03.08.2017 17.46, skrev Daniel Vetter:
On Thu, Aug 3, 2017 at 5:24 PM, David Lechner <david@xxxxxxxxxxxxxx> wrote:
On 08/03/2017 09:58 AM, Noralf Trønnes wrote:
Hi,
The tinydrm/repaper driver is monochrome, but I have just used an
emulation format XRGB8888, since monochrome support is scarce in
userspace. I'm using ITU BT.601 to convert from rgb to greyscale and
then use the msb for monochrome.
Now I'm asked if we can implement Floyd–Steinberg dithering in the driver
to make it more useful, so userspace can work reasonably well with
default tools/libs. I did have that in the first stage of the driver
development, but decided against it, since I figured this was the
responsibility of userspace not the kernel. But personally it doesn't
really matter to me either way.
So the question is, can I say yes to such an addition?
IMHO, if we add monochorme/grayscale support to DRM, then I think using
dithering for the "compatibility mode" XRGB8888 emulation would be a good
idea. But until then, I don't think I would like it because unless you are
displaying photos it will probably causes some noticeable distortion.
I'd suggest for monochrome displays we forgo dithering entirely. The
XRGB8888 stuff is just there to make sure userspace can expect that
format to work, but that's it. If you want your greyscale to look
good, then pls directly render greyscale in userspace.
There's 15+ years of history on why drm doesn't do any rendering in
the kernel, and there's reasons for that. XRGB8888 really was an
exception since otherwise normal distro's won't even boot up, but
that's going to be the _only_ exception. And we're going to make it
work with the minimal amount of kernel code, i.e. no fancing
dithering, scaling, interpolation or anything like that.
Thanks for clarifying, now I have some real arguments instead of just a
hunch.
Noralf.
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