Three.js ShaderMaterial with lights on mesh imported from Blender - three.js

Question

I'm trying to get a ShaderMaterial with lights working in three.js r77. It works correctly when applied to a mesh with a simple BoxGeometry but it behaves incorrectly when applied to a mesh imported from Blender.
A simple jsfiddle illustrating the problem is here. The mesh on the left is created from a Blender export. The mesh on the right is created from a simple BoxGeometry. Both are using the same ShaderMaterial. The position of the light is indicated by the DirectionalLightHelper.
The mesh on the right is being lit correctly, while the mesh on the left is not. Clearly the problem is in my shader code. I initially assumed that the problem is in the UV map on the imported mesh, but that does not appear to be true. In the jsfiddle example the UV map is copied directly to the BoxGeometry mesh from the imported geometry---they're rotated relative to each other because of the coordinate differences between Blender and three.js, but the lighting is still working correctly on the mesh on the right with the imported UVs.
The shader code is:
THREE.TestShader = {
uniforms: {
"uDirLightPos": {
type: "v3",
value: new THREE.Vector3(20, 20, 20)
},
"uDirLightColor": {
type: "c",
value: new THREE.Color(0xffffff)
},
"uTexture": {
type: "t",
value: null
},
},
vertexShader: [
"varying vec3 vNormal;",
"varying vec3 vViewPosition;",
"varying vec2 vUv;",
"void main() {",
"vUv = uv;",
"vNormal = normalize(normalMatrix * normal);",
"vec4 mvPosition = modelViewMatrix * vec4(position, 1.0);",
"vViewPosition = -mvPosition.xyz;",
"gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);",
"}"
].join("\n"),
fragmentShader: [
"uniform vec3 uDirLightPos;",
"uniform vec3 uDirLightColor;",
"varying vec2 vUv;",
"varying vec3 vNormal;",
"varying vec3 vViewPosition;",
"varying vec4 mvPosition;",
"uniform sampler2D uTexture;",
"void main() {",
"vec4 lDirection = viewMatrix * vec4(uDirLightPos, 0.0);",
"vec3 lVector = normalize(lDirection.xyz);",
"vec3 normal = normalize(vNormal);",
"float diffuse = dot(normal, lVector);",
"vec4 texel = texture2D( uTexture, vUv );",
"gl_FragColor = vec4(uDirLightColor * diffuse, 1.0) * texel;",
"}"
].join("\n")
};
In addition to a solution to this particular problem, a pointer to better documentation on the three.js shader stuff would be appreciated. The official documentation for ShaderChunk, ShaderLib, and UniformsLib is not what you'd call exhaustive.

Answer 1

Your Blender-exported model has incorrect normals.
vnh1 = new THREE.VertexNormalsHelper( mesh1, 1, 0xff0000, 1 );
scene.add( vnh1 );
fiddle: https://jsfiddle.net/5j0axcgz/1/
three.js r.77