[Bf-committers] Antw.: Is Cycles going to support OpenCL 1.0 ?

Brecht Van Lommel brechtvanlommel at pandora.be
Thu Dec 8 14:20:54 CET 2011

Let me try to explain the current situation:

The main missing feature is float3 support, though we found now that
for ATI/apple, there seems to be a bug in their 1.1 drivers related to
that, and we found a trick to avoid using it yesterday. That might
help getting things working on older ATI's, but again, their driver
currently can't even compile the full kernel. I'd love to have Cycles
running on any GPU and have spent weeks working on OpenCL/ATI support,
but progress is slow.

We don't want to be biased towards NVidia, but they've got one major
hardware/compiler advantage, which is that not all functions need to
be inlined. Without this every feature that is added puts more stress
on the compiler, making it crash or run out of memory. With the next
AMD driver release (which includes a bugfix they did for us), it looks
like we'll be able to support basic path tracing, but without
transparent shadows, improved closure sampling and procedural
textures. Probably that will be in 2.62.

The only other GPU raytracer with ATI support (that I know of and
isn't a research prototype) is SmallLuxGPU, and they are also limited
in features and fighting compiler issues. V-Ray RT (OpenCL), Octane,
Arion and iRay (CUDA) are all NVidia only still.


On Thu, Dec 8, 2011 at 12:43 PM, Antony Riakiotakis <kalast at gmail.com> wrote:
> On 8 December 2011 13:06, Thomas Dinges <blender at dingto.org> wrote:
>> Well, I don't think we need to discuss that. AMD 4xxx cards were not designed for OpenCL, the support was added later via driver. It's the same on nvidia, the Femi cards were the first, designed for CUDA.
>> The fault is therefore not on our side and discussions won't solve it. ;)
> This is hardly a good reply. Of course OpenCL support is added through
> the driver, hardware simply executes opcodes. The support was added
> after all, so people still expect to be able to use it. A discussion
> will make people understand so it solves any suspicions of bias. My
> understanding is that certain features or extensions either run on
> software or are missing. If people can know them though, and know
> their importance they can be more understanding. And more importantly,
> they can stop feeling that the developers are biased towards NVIDIA.
> Anyways, here are some references:
> http://developer.amd.com/sdks/AMDAPPSDK/pages/DriverCompatibility.aspx,
> where you can clearly see that GPUs have beta OpenCL support
> (unfortunately couldn't find the conformance results)
> http://developer.amd.com/sdks/AMDAPPSDK/assets/AMD_Accelerated_Parallel_Processing_OpenCL_Programming_Guide.pdf,
> where, if you check under AppendixD the lowest GPUs mentioned are
> series 5.
> http://developer.amd.com/sdks/AMDAPPSDK/assets/AMD_APP_SDK_Getting_Started_Guide_v2.4.pdf
> check section 5 supported devices, where all the features supported
> are enumerated.
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