Beginning with Gem 0.92, the following has become a standard feature provided by the [GLdefine] object.
If you use Gem 0.92 or later, info on this page is obsolete.
glMacro object for Puredata/GEM
An object to handle macros listed in "gl.h" for those who want to use low-level OpenGL wrapper objects..
The object will either output a float from its outlet, or an error message to the console if the macro does not exists.