Is OpenGL ES suitable for performing skeletal animations?

Question

I have to start a 3D-Project for mobile platforms. First of all I would like to outline the main aim - skeletal animation. As for the solution I was thinking of OpenGL ES and C++. So the questions are:

1. Is OpenGL ES robust enough to handle skeletal animation (including those skinning shaders)
2. Is OpenGL ES supported widely across mobile platforms, and what are the most famous ones? (for instance, is iPad supported?)
3. Is this possible anyway, I mean will I have enough computation power?
4. Is it worth using XNA math library, because of its SIMD optimization (though I'm really unsure that SIMD is supported on mobile platforms, but who knows...).
5. Is it good to use C++ for this? If yes, then which compiler should I choose for development and testing? Moreover, I have no clue what compilers are used for mobile platforms?

As you might have got it - I've never programmed for mobile platforms yet. Therefore, some general recommendations are welcome.

Answer 1

Yes, OpenGL ES 2.0 can handle vertex skinning for skeletal animations quite well. OpenGL ES 1.1 used a fixed function pipeline, without shaders, so it's harder in the older API to do this, but 2.0 adds support for shaders. OpenGL ES 2.0 is present on all shipping iOS devices (the iPhone 3G S and newer supports it, including both iPads), as well as almost all Android devices (I could only find a couple of very low end handsets that didn't). Windows Phone 7 doesn't appear to support OpenGL ES, but I believe BlackBerry does.

If you're interested in this, I highly recommend reading Philip Rideout's book "iPhone 3D Programming". While it has "iPhone" in the title, he uses generic C++ for almost all of the code in the book, so it should translate to other platforms well and should be easy for you to understand. He even has a section in the "Optimizing" chapter with code for performing vertex skinning on OpenGL ES 2.0 and even 1.1. You can grab the sample code for the book here, including a demonstration of this skinning.

C++ is supported on iOS through Objective-C++, where you could set up the platform-specific UI elements in Objective-C and then do all your backend and rendering logic in C++. Again, Philip does this in his book, and you can see in his source code example applications how he structures this. The people at Imagination Technologies have also set up some platform-agnostic scaffolding in their PowerVR SDK, which some people have used for quickly getting their 3-D rendering up and running on mobile devices. Also in that SDK are some great documents about moving from OpenGL to OpenGL ES, as well as performing various effects on these GPUs.

I have heard of some people getting slightly better performance for small vertex sets by performing transformations on-CPU (on iOS this can be done using the Accelerate framework), but I'd imagine that vertex shaders would be much faster for larger geometry. The PowerVR GPUs that I've worked with in mobile devices are much more powerful than you'd think, particularly the new one that ships in the iPad 2.

You'll need to use the Xcode IDE, with either its GCC or LLVM compiler to target iOS devices, but I believe Android has a few more options in that regard.

Answer 2

In short:

1. Yes, of course. Why not?
2. Yes, I suppose. What else? DirectX definitely not.
3. Yes, I suppose. But depends on what else you want to do.
4. No, at least not just because of SIMD, as I suppose it is not much supported on mobile platforms, at least the SIMD instructions XNA is optimized for.
5. Yes, why not? I think the i...s mostly use Objective-C, but there should be compilers for C++, too. Just ask google, as I also don't have any mobile experience.