Re: [Gegl-developer] OpenCL support in GEGL is almost there

[johannes hanika <hanatos gmail com>]

hey!

good news, and congrats on putting it into gimp.

actually darktable's pixel pipeline was based on gegl as the project
started (you'll still notice some #ifdef HAVE_GEGL if you look around
the code closely). that was 2-3 years ago and at that time it turned
out a simple DIY pipeline was a lot faster, to a point where it just
didn't seem practicable to use gegl. that said i love the clean gegl
api and would totally love to see dt/gimp use the same rendering api
and have some compatible interchange format.

i guess the biggest issues back then were:

- processing the image as a whole, not just the region of interest at
the currently visible scale. darktable pre-downsamples and processes
only these pixels (comes with issues, mostly works fine).

- i had the feeling that even resampling the image to these small
tiles came with a huge overhead

- we have plugins that need filter radii of 128px or more. so tiled
processing is hard to make fast.


these are some crucial features for us:

- needs to be fast (1Mpix < 100ms if possible, our equalizer is on the
limit). that's because we always process the whole pipe potentially,
might be 20 active plugins and you want interactive feedback.

- easy to insert a cache (we cache the input to the plugin the user is
currently tweaking for example).

- i mentioned the large filter radius overlap thing before. mostly for
bilateral filtering (reasonable filter size might be ~30% of the image
width) and the edge aware wavelets.

- we have esoteric pixel formats (bayer patterns, in 16-bit and in
32-bit float, etc.).

- we have huge problems with memory usage.


also our opencl support is great, fast, stable, and doesn't need to be
there compile-time. which makes it easy for users to fall back to the
cpu code path, which in practice happens for every system or driver
update.. so i guess i'm saying the cpu codepath is very important to
us, too, and we spend some considerable time optimizing it
(threading/sse and such).

cheers,
 jo


On Wed, Apr 11, 2012 at 6:04 AM, Victor Oliveira
<victormatheus gmail com> wrote:
> Hello everyone,
>
> I'm a GEGL developer and I've been working since last year implementing
> OpenCL support in GEGL. We have for now:
>
> - An API to write OpenCL point and area operations
> - A way to share image data between operations in the GPU (so we don't have
> to bring the image back and forth the CPU for each operator)
> - +20 GEGL operations have OpenCL support already
> - It's fast
> - It's been included in GIMP 2.8RC1
>
> Darktable has its own OpenCL support code (which is pretty good, by the
> way). I'd like to start talks to avoid work repetition in both programs and
> to make an argument pro-GEGL use in Darktable :)
>
> bye!
> Victor Oliveira
>
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