blender-archive/source/blender/gpu/shaders/material/gpu_shader_material_camera.glsl

void camera(out vec3 outview, out float outdepth, out float outdist)
{
  vec3 vP = transform_point(ViewMatrix, g_data.P);
  vP.z = -vP.z;
  outdepth = abs(vP.z);
  outdist = length(vP);
  outview = normalize(vP);
}