[webkit-dev] Some thoughts on WebCL

Filip Pizlo fpizlo at apple.com
Fri Apr 19 22:20:49 PDT 2013

On Apr 19, 2013, at 10:17 PM, Zoltan Herczeg <zherczeg at webkit.org> wrote:

> Hi,
>> First, we think of WebCL more like a specialized toolbox for
>> JavaScriptlibrary providers, specifically those targeting compute
>> intensive use
>> cases. Areas such as image/photo editing, video and audio processing,
>> physical simulation, data visualization are natural candidates. That said,
>> it is unrealistic to expect every web developer to take WebCL and create,
>> say, a new vision library. Nonetheless, libraries using WebCL would be of
>> interest to large groups of developers simply because of the performance
>> gains.
> I think this is the key part of the announcement. WebCL can solve problems
> which has no efficient JS based solutions. Not at least in the foreseeable
> future.
>> Another issue that has been mentioned are potential security concerns.
>> WebCLuses "compute kernels", which like
>> WebGL shaders, are written in a C-like language. WebCL kernels can use
>> pointers to potentially access memory that should not be visible to the
>> application. This could compromise the browser or even the host device.
> Yes, you can easily read the whole GPU memory.
> I hoped WebCL improves the syntax of OpenCL. E.g using array references
> instead of pointers. If I understand correctly, the "WebCL Kernel
> Validator" re-compiles all kernels, so you could also enhance the syntax.
> Especially in the JS side. An example for your slides:
> kernel.setKernelArg(0, inputBuf);
> kernel.setKernelArg(1, outputBuf);
> kernel.setKernelArg(2, count, WebCL.KERNEL_ARG_INT);
> This is OK in C, but really ugly in JS.
> Why not:
> kernel.setKernelArg(inputBuf, outputBuf, WebCL.asInt(count)); ?
> Both NULL and null is used in various examples. This is not nice as well.
> Or this example:
> <script>
> var bpp = 4;
> // bytes per pixel
> var pixels = new Uint8Array(width * height * bpp);
> var pitch = width * bpp;
> var clImage = context.createImage(WebCL.MEM_READ_ONLY, {channelOrder:
> WebCL.RGBA, channelType:WebCL.UNORM_INT8, width:width, height:height,
> pitch:pitch } );
> </script>
> I don't see a binding between the pixels and the clImage variables. Would
> be better to define only the clImage, which would be an Uint8Array in the
> same time.
> What about error handling?
>> Some alternatives to WebCL have been mentioned in the mailing list. These
>> include Intel's ParallelArray and some form of beefed-up web workers.
>> These
>> other approaches do not necessarily conflict with WebCL since their focus
>> is not really GPU compute. We do see some definite benefits for WebCL.
> This is also a key thought. OpenCL is designed for highly parallel, but
> otherwise very simple tasks. Its primary use case is extending WebGL.
> However, we still need a parallel JS based solution, which can access the
> GUI in some way.


> Regards,
> Zoltan
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