Posted by Sven Gothel on Jul 14, 2014; 1:15pm
URL: https://forum.jogamp.org/Need-Help-Solving-OpenGL-GLSL-4-4-Issues-tp4032557p4032561.html

I don't see where you clear the
depth buffer via GL_DEPTH_BUFFER_BIT ..

<https://www.opengl.org/wiki/Depth_Test>

Note on coordinate system:
====================
You use the device default coordinates,
which are in normalized device coordinates (NDC)
[-1..1] for the x- and y-axis.
The z-buffer semantics depend on the depth range,
which defaults to [0..1]

<https://stackoverflow.com/a/7770714>
<https://www.opengl.org/wiki/GLAPI/glDepthRange>