getExtension method
Implementation
getExtension(String key) {
Pointer _v = gl.glGetString(EXTENSIONS);
// print("OpenGLES getExtension key: ${key} _v: ${_v} ");
String _vstr = _v.cast<Utf8>().toDartString();
List<String> _extensions = _vstr.split(" ");
// on iOS crash ...
// calloc.free(_v);
return _extensions;
}