three.js/src/renderers/shaders/ShaderLib/depth_vert.glsl

#include <common>
#include <morphtarget_pars_vertex>
#include <logdepthbuf_pars_vertex>
#include <clipping_planes_pars_vertex>

varying float vViewZDepth;

void main() {

	#include <begin_vertex>
	#include <morphtarget_vertex>
	#include <project_vertex>
	#include <logdepthbuf_vertex>
	#include <clipping_planes_vertex>

	vViewZDepth = - mvPosition.z;

}