javascript - Three.js wireframe model from .vtk file -

i've been trying replicate results of three.js's wireframehelper using shaders. want display wireframe using geometry information. using vtkloader used in examples, , have been basing code off of jsfiddle example.

i have created jsfiddle example highlight problem.

the model loads correctly, shader seems draw edges of select faces. have not been able figure out why triangles not drawn edges.

is because loading data .vtk file (missing data or bad loader)? think data fine since built in wireframehelper able correctly draw triangle edges, otherwise don't know why triangles drawn not others.

i using common shader, don't think problem.

<script type="x-shader/x-vertex" id="vertexshader">     attribute vec3 center;     varying vec3 vcenter;      void main() {         vcenter = center;         gl_position = projectionmatrix * modelviewmatrix * vec4(position, 1.0);     } </script> <script type="x-shader/x-fragment" id="fragmentshader">     #extension gl_oes_standard_derivatives: enable     varying vec3 vcenter;      float edgefactortri() {         vec3 d = fwidth(vcenter.xyz);         vec3 a3 = smoothstep(vec3(0.0), d * 1.5, vcenter.xyz);         return min(min(a3.x, a3.y), a3.z);     }      void main() {         gl_fragcolor.rgb = mix(vec3(1.0), vec3(0.2), edgefactortri());         gl_fragcolor.a = 1.0;     } </script> 

my guess weird vtkloader, has had problems example loaders threejs.org?