Shady Business

I was surprised to find that OpenGL ES 2.0 does not have support for a fixed function pipeline (FFP) at all. You have to use shaders. Obviously, shaders are powerful and give you a level of flexibility that is not possible with a FFP. Unfortunately, it also means that you have to implement all the calculations of the FFP yourself, even when all you really need are the simple features that the standard FFP provides out of the box in OpenGL ES 1.x.

Initially, this means more work to get something to show up on the screen, but once you have implemented a basic shader, you will have a template to start with for future shaders, so it's really only a one-shot effort.

I wrote my first shader in a sort of shader assembly language back in 2001. Since then various high level shader languages have appeared, which makes writing shaders much less of a pain in the nether regions. I believe HLSL and GLSL are the most well known shader languages and unless I am mistaken the OpenGL ES has its own variation of GLSL called OpenGL ES Shading Language. I highly recommend learning about the shader assembly instructions even if you are only going to use a high level language, because it gives you a better understanding of the fundamental functionality of the shader hardware.

While I have written a lot of shaders over the last few years, I have exclusively been using HLSL, because I have been using the XNA framework on the Xbox 360. The underlying concepts should essentially be the same so hopefully I will be able to pick up the ES shading language quickly. As soon as I have a working example shader, I will post my findings here.

Comments: 0 Tags: iPhone, OpenGL, Shaders