Parallax Occlusion Mapping with GLSL

hey,

I’m currently trying to get this to work so I was hoping to find some implementations online. Unfortunately the only thing I found was a HLSL implementation that was using texture gradients in the fragment shader. Unfortunately I’m running on OGL version 2.1.2. where the extension of the corresponding functions isn’t supported, yet.

Is there a possibility to implement this without texture gradients? Are there maybe even implementations out there?