OpenGL for Android and iPhone

Question

In discussion with some colleagues we were wondering whether OpenGL work developed for Android or iPhone are effectively interchangeable given that both support the spec.

Or is the reality of sharing OpenGL between the two platforms more a case of quirks, tweaks and not as easy as one might have hoped.

Answer 1

Both platforms use OpenGL ES, but Wikipedia claims that Android uses 1.0 while the iPhone uses 1.1 (original and 3g) an 2.0 for the 3gs link. It's likely that at least some programs will use api functions not included in 1.0, so there won't be full compatibility between the 2 (well 3).

Answer 2

OpenGL ES on Android is done according to Khronos Java GLES spec JSR239 , and wraps GL calls in something like glinst.glBindBuffer(FloatBuffer.wrap(data) ... ) OpenGL ES on iPhone is done using stock GL.h files and the same call will just look like glBindBuffer(data...)

The code will not be interchangeable and will cause many quirks, even before you get into the whole mess of differences between 1.0 1.1 and 2.0 APis.

Answer 3

An OpenGL implementation normally consists of two parts: 1. Platform specific part. This has function usually related to creating and displaying surfaces. 2. The OpenGL API. This part is the same on all platforms for the specific implementation of OpenGL, in the case of Android, OpenGLES 1.0.

What this means is that the bulk of your OpenGL code should be easy to port.
In C, you might have glLoadIdentity();
In Java on Android, something like gl.glLoadIdentity();

So for the bulk of your code you can cut and paste, and then search and replace prefixes like 'gl.'

Now for the fun part: you really need to be careful what version you are coding against. OpenGL for the desktop has APIs which don't exist in OpenGLES. There are also some OpenGL data types specific to each platform. In addition, you have 1.0 (e.g. Android) 1.1 (e.g. iPhone) 2.0 (e.g. iPhone GS) to deal with. The differences in API often have to do with additional hardware capability, so it's not like you can write some easy wrapper code to emulate 2.0 features in 1.0/1.1.