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

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.