   POM HLSL - GLSL and tex2Dgrad
  hi,I've already noticed that I'm not the first one trying to convert the gamedev parallax occlusion mapping algorithm from HLSL into GLSL.Most people had problems with the following partfloat2 dx, dy;dx = ddx( IN.texcoord );dy = ddy( IN.texcoord );while ( nCurrSample < nNumSamples ){   vCurrSample = tex2Dgrad( Sampler, IN.texcoord + vCurrOffset, dx, dy );   if ( vCurrSample.a > stepHeight )   {   //...   }}because tex2Dgrad wasn't supported in GLSL. However they talked about an extention GL_ARB_shader_texture_lod where this function should be supported. Now, I'm actually a really big noob in those things so does this extention already exist? Where can I read about it? Where can I get it? How do I use it?Are there already some POM GLSL implementations out there? All that I found were some faulty algorithms from '06 or sth. Am I looking in the wrong places?I kinda feel overwhelmed by all of these stuff but I'm working on my thesis so I need to get used to this stuff as fast as possible.   
  All extension documents are stored in the OpenGL Extension Registry.For that particular extension, you can get the specification for it here;  Thanks.I now read through this a little bit but I'm still struggling with "installing" an extension.For example I wanna use the texture2DGradARB function from GL_shader_texture_lodMy glext.h looks like this at this point.#ifndef GL_ARB_shader_texture_lod#endifThe other extensions have function pointers defined in this area so do I have to do sth like that?#ifndef GL_ARB_shader_texture_lod#define GL_ARB_shader_texture_lodtypedef void (APIENTRYP PFNTEXTURE2DGRADARBPROC) (sampler2D sampler, vec2 P, vec2 dPdx, vec2 dPdy);#endifIf yes then it doesn't recognize what sampler2D is so what do I do wrong?   ;  GL_ARB_texture_shader_lod only adds functions to GLSL, so they aren't in any header, just add:#extension GL_ARB_shader_texture_lod : requireTo the top of your GLSL shader, and use the functions defined in the extension spec.   