Standard syntax for writing to FBO:
layout(location = 1) out vec4 colOut; ... colOut=col;
Assuming the FBO texture attached has the FBO id fboc, am I constrained to writing to fboc at the set of coordinates associated with colOut, or can I offset the texel colOut will write to? What I have in mind is generating a shadow map for the floor:
if the fragment belongs to an occluding object: calculate the vector from the light to this fragment; extend the vector away from the fragment foreach texel coincident with the vector darken it.