#version 150

out float logz;

uniform float z_near, z_far;

const float C = 0.0001;
float FC = 1. / log(z_far * C + 1.);

void main(void) {
	vec4 pos = qgl_ftransform();
	logz = log(pos.w * C + 1.) * FC;
	gl_Position = pos;
}