GLSL check if fragment is on geometry

Question

I am currently writing the positions of my geometry to the RGB channels of gl_FragColor and I would like to write 1.0 to the alpha channel if the fragment is part of geometry, and 0.0 if its empty.

Is there a simple way to tell if a fragment is geometry or not? Maybe through gl_FragCoord.z?

thanks

Answer 1

Every processed fragment is generated because the geometry is rendered. Fragments not belonging to the geometry rasterization result are not processed by the fragment shader.

So, the solution is very simple:

gl_FragColor.a = 1.0;

However, you need an RGBA texture.