Posted by jmaasing on Feb 12, 2014; 5:50pm
URL: https://forum.jogamp.org/Shader-does-not-accept-the-Parameters-tp4031551p4031552.html

Shader compilers are allowed to optimize away "in" parameters (and uniforms) that are not used in the shader program. So even if "a_position" is declared in the shader, if it is not used you can get -1 as result.