1. Please read my previous comment that if you compile using Lazarus 2.0.6 you must uncomment an IFDEF so the new SortIndicator is not used. If you want to use this feature, you must update to the developmental version of Lazarus (Trunk).


2. Please read the web page you linked: https://github.com/rordenlab/MRIcroGL12 - it notes that you must install the Metal-Demos repository and you will want to make sure your MRIcroGL project has this folder in its path (with MRIcroGL project open in Lazarus, choose Project/ProjectOptions/Paths and make sure the other unit files points to ../Metal-Demos/common;

3. Specifically for Windows you can adjust whether a faster static library is used. For example, I my have Project/ProjectOptions/Paths providing the link to ../static/x86_64-win64 which includes the faster static library from https://github.com/synopse/mORMot - but if you want to skip this just comment out the FastGZ directives in nifti.pas and mat.pas. You will be alerted of these options when you try to compile on Windows with your path not set correctly
 //Windows: if you get an error "Can't find object file" you can copy the 'static' folder from
// https://github.com/synopse/mORMot
//Alternatively, disable "FastGZ" in nifti.pas and umat.pas


I agree that MRIcroGL1.0 is easier to build, but that is because it is monolithic. In contract, MRIcroGL1.2 is modular and this allows you to compile to either OpenGL or Metal and also allows you to build simpler projects from scratch. For example, the volume rendering core is here
   https://github.com/neurolabusc/Metal-Demos/tree/master/volumerender