I received this email from an angry customer:

“I have purchased FA2, FA3d, and FA4+gpu Module” 

“All programs rendered ok on the gpu’s ,  now this El Capitan has arrived  and none of the FA’s render on GPU  anymore .”

“They all render on the CPU ok, but the slow speed  defeats the  object of paying “

“So whats the score , do we have to wait for apple to update their drivers? “

“My Gpu  amd ati radeon hd 6770m – 2011 27inch imac”

At this point, both OpenCL and Metal Compute shaders are unusable for most GPUs incorporated in Mac products on El Capitan.

Back in Mountain Lion, the OpenCL drivers worked on EVERY GPU model shipped with Macs.

Does Apple test OpenCL/Metal with real world applications?

It is very, very easy with Fractal Architect 4.

1. Download the free app.
2.  Click the GPU Trial button to open the GPU Trial window.
3. Turn off the Enforce Quarantine, pick a GPU, then click the button under a fractal to render it.

Is this the new status quo – advertise big new features at WWDC like Metal Compute Shaders on OS X only to find them unusable when released??

Please consider that the OpenCL compiler for all Intel GPUs was unable by this app since Mavericks (due to compile issues as reported in a bug report to Apple 2 years ago).

Metal Compute shaders have no problem compiling the app’s kernels for Intel GPUs but do cause GPU hangs – never seen before on OpenCL with Nvidia/AMD GPUs. We believe these hangs are caused by debug asserts in Apple’s Metal math library when NaN values are encountered.

I have recently successfully implemented CUDA rendering for the app for Nvidia GPUs on El Capitan, but of course CUDA is not available to customers on the Mac App store. (Important because the OpenCL + Metal drivers are now broken in El Capitan)

CUDA drivers are meticulously maintained by Nvidia and are the closest thing we have to Reference GPU compute API. And they work very well on OS X.

Neither the developer nor customers have any idea if these bugs will ever be addressed. We are all totally in the dark.

When the OpenCL/Metal drivers work, they deliver huge performance increases.

We have released multiple versions of Fractal Architect using OpenCL on the Mac App Store since 2011. Today we offer rendering on OpenCL, Metal, and CUDA (but not on Mac App store).