OpenCL Extending OpenGL

OpenGL 3.0 was a disappointment to game developers who hoped the API would add some key features that ended up being left behind. With the latest release, Khronos relegated OpenGL to professional and workstation applications like CAD/CAM and 3D content creation software, foregoing the wants and desires of game programmers. While not ideal from our perspective (competition is always good), the move is understandable, as OpenGL hasn't been consistently used by any major game engine developer other than Id software for quite some time. DirectX is seen as the graphics API of choice for game programming, and it looks like it will remain that way for the foreseeable future.

But OpenCL does bring an interesting element to the table. One of the major advancements of DirectX 11 will be the addition of a compute shader to the pipeline. This compute shader will be general purpose and capable of operating on diverse data structures that pixel shaders are not geared towards. It will be capable of things like OpenCL is, though it will be tuned and geared toward doing so in the context of graphics. It is, after all, still DirectX. In DX11, the pixel shader and compute shader will share data via data structures rather than any sort of formal input/output mechanism. Because of the high level of integration, game developers (and other graphics engine developers) will be capable of tightly combining current techniques with more general purpose code that can handle a broader array of algorithms.

OpenGL doesn't have anything like this in the works, but OpenCL fixes that. OpenCL is capable of sharing data with OpenGL. And we aren't talking about copying data back and forth easily, we are talking about physically sharing data structures and memory locations. This essentially adds a compute shader to OpenGL for those who want it. Why is that the case? well, offering OpenCL users a means of using OpenGL images and buffers as OpenCL images and buffers means that OpenGL and OpenCL can share data with no copy or conversion overhead. This means that not only are OpenGL and OpenCL able to work on the same data, but that the method by which they communicate is very similar to what DX11 does to allow the passing of data between pixel an geometry shaders.

While game developers may be intrigued, the professional app developers may have more of a reason to get excited. Sure, this will allow OpenGL game developers to use a compute shader like option, but it gives professional application developers the ability to actually combine the real work of simulation or data manipulation with visualization. With support for double precision in hardware that supports it, this could be useful for applications where a lot of real work needs to be done both on the thing being visualized and the visualization itself. This could speed things up quite a bit and allow fluid realtime visualization and manipulation of much more complicated data sets.

Additionally, this compute shader will work on hardware not specifically designed as DX11 class hardware. DX11, as a strict superset of DX10, will extend some functionality to DX10 hardware, but we aren't yet certain about the specifics of this and it may include CS functionality. On top of this, OpenCL should get drivers in the first quarter of next year. This puts the combination of OpenGL 3.0 plus OpenCL 1.0, for the first time in a long time, ahead of DirectX in terms of technology and capability. This is by no means a result of the sluggish and non-innovative OpenGL ARB. But maybe this will inspire more use of OpenGL, which maybe will inspire more innovation from the ARB. But I'm not going to hold my breath on that one.

In any case, the fact that OpenGL and OpenCL can share data without requiring a copy or conversion is a key feature. Not only will OpenCL allow developers to use the GPU for general purpose computing, but using OpenCL with OpenGL will help build a bridge between data parallel computing and visualization. Existing solutions like CUDA and Brook+ haven't done very well in this area, and using OpenGL or DirectX for data parallel processing makes it difficult to get work done efficiently. OpenCL + OpenGL solves these problems.

And maybe we'll even see things go the other way as well. Maybe developers doing massive amounts of parallel data processing using OpenCL not formerly interested in "seeing" what's happening will find it easy and beneficial to enable advanced visualization of their data or the processing thereof through integration with OpenGL. However they are used together, OpenCL and OpenGL will definitely both benefit from their symbiotic relationship.

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  • yyrkoon - Saturday, January 03, 2009 - link

    Apparently I *am* more knowledgeable than some here. How you can twist the context of comments to your misguided reasoning ( that I favor Microsoft ) is beyond me. Do I prefer Windows to OSX ? Yes. Why? Because maybe Microsoft is not perfect, but at least they do not force unwanted hardware on me to use their software.

    Windows is the only real gaming OS. Period. And I suppose my comment about Cross platform applications, and other good strong possible uses in a *NIX environment fell on deaf ears too( uses for OpenCL ).

    There is nothing wrong with OSX, it is after all based on BSD. However I will not over pay for hardware *just* to use it either. There are too many free operating systems that are just as good. If I need Windows application compatibility, I will just run Windows. Apple offers me *nothing* I have to have.

    Now, who here is truly blind ?

    Reply
  • melgross - Saturday, January 03, 2009 - link

    You just want to think you are.

    You have gaming on the brain. I guess you must BE a gamer as that's all they think about anyway.
    Reply
  • Penti - Saturday, January 03, 2009 - link

    Really who cares about the gaming? This isn't a physics framework or engine.

    It can be used in games, but this isn't really about a discussion on Apple gaming. That's not really why it can "speak" to each other.

    Apple got a lot of professional applications that today uses the open standard OpenGL like photo editing, video editing, VFX and others (scientific apps etc) on their platform, for not only graphics but for gpgpu, from not only them selfs but from vendors such as Adobe and Avid. Most of the apps also use OpenGL for acceleration in Windows too. Besides that, OpenCL will be available for handheld devices such as mobile phones. Even though Microsoft does software for phones you won't see DX11 or GPGPU there. Not that I'm an Apple fanboy, but I can see why Apple builds on what's already around and extends OpenGL and free standards. They can't rely on close standards, most of their apps (other vendors for OS X) are to some degree cross platform as they should be. CUDA is already available on the Mac too. But you can't expect them to run DX. This isn't about Apple as an OEM either. It's about software (Microsoft does hardware too). It's engineered to fit a wider picture and a wider array of devices including Windows, there isn't anything bad about that. There isn't anything bad about getting consumer and professional apps a boost in using GPGPU. It's certainly what some ISVs want. Theres more then gaming in the world. Microsoft are free to do whatever and nobody has said that they aren't best on games, but people are also free to criticizes and complain about Microsoft, just as they are about Apple and there certainly is a lot to be criticizing both about. Apple for certain can't just be catering to it selfs, not when they and their software vendors want something else. Microsoft essentially can. As most are already deeply invested in Microsoft tech and soft. That doesn't mean Windows users can't benefit from the Apple developed OpenCL. Their certainly is Windows only apps that will use it. Even non OpenGL ones. It's not only a cross platform library.
    Reply
  • Atechie - Friday, January 02, 2009 - link

    Drop the Apple-preaching, it's uninteresting as Apple is neither HPC nor the mainstay platform for CUDA/Brook+/OpenCL.

    .oO(I swear, Apple-jocks are like religious zealots, they can stop pushing their religion down everbody elses throat...interested or not.)
    Reply
  • melgross - Saturday, January 03, 2009 - link

    Yeah, just like people like you who do the opposite?

    Why mention the company who did all the work, as long as it's Apple? Right? That' makes people fanboys if we think a proper mention should be made?
    Reply
  • Shadowself - Friday, January 02, 2009 - link

    So anyone says anything positive about Apple and immediately that equates to being an Apple zealot? It appears more likely that your personal bias is showing.

    It is absolutely true that Apple's Mac has NEVER been a gamer's platform -- and it probably never will be. Additionally, Apple has never fully supported (or even properly supported, IMHO) any development other than their core groups (K-12, Undergraduate to some extent, graphics and motion picture artist communities, and publishing). Thus Apple supports low to mid range graphics card and very high end 3D cards -- but absolutely nothing for the moderate to high end gamer.

    However, Apple did do the vast majority of OpenCL before submitting it to become an open standard. Apple wants to expand its role in the graphics and motion picture communities. The only way to do this was to do something like OpenCL. Additionally, Apple knew that a completely closed set of APIs was not going to gain any traction. Thus they submitted it as an open standard and gave up control of it.

    Not mentioning that Apple did the majority of OpenCL is wrong. For anyone to claim Apple did this altruistically is wrong. To bash Apple for coming up with something that has become a cross platform standard that can utilize both AMD and nVidia cards as well as a host of other hardware is wrong.
    Reply
  • yyrkoon - Thursday, January 01, 2009 - link

    I never said it wasn't true. Let us just say that I am less than inspired to even bother looking. OpenGL is very low on my personal list of priorities, and I could care less what Apple does( unless perhaps if someday they compete head to head with Microsoft ).

    Still, no matter how much I like or dislike OpenCL, chances are pretty good that on Windows platforms, it is going to be rendered( pun? ) moot. Maybe it will make the next greatest XGL even more powerful, so all those people who like to play with their application windows in linux can spend all day every day bragging/ making youtube videos about how their desktop UI can do *this*, and *that* while remaining even less productive than before ; )

    Yes, the above is sarcasm to some extent, but it also true to an extent as well. OpenCL will help those who prefer and alternative to Windows do similar things without having to own Windows. Scientists who want to use GPGPU(s) to crunch some serious numbers, etc. What it will not do however is make the majority of gamers out there happy. *Unless* the majority of game developers start using OpenGL/CL on the Windows platform( Which is very unlikely ). Certain cross platform applications however could benefit, sure.
    Reply
  • Penti - Friday, January 02, 2009 - link

    So OpenCL and OpenGL is bad because it's cross platform and open standard? If you look at who's involved you see companies like ARM and embedded computing companies, they can't really use anything like DX11. This isn't just for games but GPGPU in general.

    It's not like there isn't apps using OpenGL on Windows either. But it's rather about a broader spectrum then owning or not owning Windows. It's for a wider category of devices then DX11 is. You won't have DX11 cellphones. But you will have OpenCL on the next gen Sony and Nintendo consoles, handhelds, settopboxes etc. In HPC too, there will be libraries/frameworks to help you out.

    Of course theres professional apps such as Photo-editing, video-editing and encoding, VFX, CAD / GIS, math and other engineering software that could benefit widely from Open CL. And a lot of them are cross-platform. Or at least would need the OpenCL on for example the Mac. Where they might have many customers.
    Reply
  • kevinkreiser - Wednesday, December 31, 2008 - link

    a while back i published a paper that involved performing an iterative deconvolution on the GPU. the point of the paper was that we could do it in real-time and use it on videos with arbitrary spatially varying blur kernels.

    anyway the largest overhead was copying the render target (single iteration of the algorithm) to initialize the next iteration. if dx11 and opencl allow the gpu and cpu to work with the same memory, without the need to copy between the two, this will speed up gpgpu apps tremendously.
    Reply
  • has407 - Monday, January 12, 2009 - link

    OpenCL itself is neutral; it provides both explicit copy and map functions, in both synchronous and asynchronous forms. Obviously what works best will depend on platform capabilities and run-time intelligence (e.g., copy/map optimizations based on platform capabilities and program behavior).

    However, that still doesn't necessarily allow for a large mapped/shared memory between the CPU and CPU. That and its efficacy is going to be implementation dependent and OpenCL has simply defined a model that should be portable and useful, even if suboptimal on a given implementation--but if you know enough about the implementation, gives you sufficient optimization choices.

    That requires some constraints on the memory model, in particular the consistency/correctness of various memory regions with respect to computational elements at different points and times, and especially with respect to mapped memory (NB: sec 5.2.8.1 of the spec).
    Reply

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