Apple launched a library – GLKit – that makes iPhones handle OpenGL properly.
Most of the people writing tutorials on the web don’t know how to use it, and so they ignore it. The few tutorials I found that mentioned GLKit were written by people who clearly didn’t read the docs, and they did some silly stuff (like re-writing texture-loading from scratch, when it’s a 2-line method call in GLKit. Apple has already done the hard work for you! Doh!)
After reading the docs (!) and a bunch of trial and error, we got it working quite nicely – and it’s a big time-saver in several areas, while sticking to standard OpenGL. Nice!
Things you need to know about GLKit
- Only works in iOS 5 and later
- Works on all hardware (assuming the hardware can run iOS 5 or later)
- OpenGL ES 1.1 has been removed/ignored; you can still use ES 1.1 features, via a simple compatibility layer – which isn’t documented (but we worked it out in the end)
- Apple provides a full Vector and Matrix library – all the core methods (cross-product, normalization, etc) are implemented for you
- Apple’s classes appear to work fine. Please don’t re-implement your own cross-product just to prove you can get it subtly wrong 🙂
- NB: if you use Apple’s Vector and Matrix classes, your code will be automatically compatible with everyone else on iOS who does so. This would be a good thing…
- Texture loading is massively simplified – just 1 method call to load arbitrary Image files as textures, and a couple of properties to set if you want to configure them
- Apple has finally deleted their HORRIBLY broken Xcode template for OpenGL projects (the one with the coloured square), and replaced it with one that works correctly (and is configured correctly)
- The iOS 3 and iOS 4 Xcode templates would disable 3D by default, for no apparent reason (depth buffer disabled). Not a good template to start from!
- … and they used a strange-shaped rectangle on screen – but stretched it to look like a square, and claimed it was a “square” … because the person at Apple who wrote the project had a major bug they didn’t understand, and just hid it under the carpet (instead of fixing it)
Creating an ultra-simple OpenGL app using Xcode 4 and GLKit
Out of the box, Apple’s templates for Xcode 4 do NOT include a basic OpenGL project. Instead, you have a good quality project that’s customized to do OpenGL ES 2 shaders.
That’s great, but a huge amount of the code out there is pre-shader, and if you just want to update / port your iOS 3 apps – or if you don’t need shaders right now – you need to delete a big chunk out of the template. And you have to add back in a couple of small items that got left out.
…I was planning to include a sample project here, cut-down from Apple’s template, but Apple broke their templating system in Xcode 4 (removed lots of features that many developers made use of. No explanation given, no alternatives provided). Given how few people are using non-shaders / GL ES 1.1, I’m not sure it’s worth finishing and posting here.
If you *really* need / want it, please post in the comments, and I’ll dig it out and see how much I can make it work with current/latest Xcode (currently: 4.5 / 4.6)