java - Normals transforming, but lighting still weird? -

i have basic model viewer displays parsed obj model. have light positioned camera is, model being viewed lit on 1 side. reason, transformations aren't doing expected in renderer. when rotate model 90 degrees x- or y-axis, mesh dark. rotate 90 degrees, , lit again.

am doing transformations wrong? or normals wrong begin with?

i calculated , applied proper transform normals in app (transpose of inverse of modelview matrix)

matrix.invertm(mnormalmatrix, 0, mmvmatrix, 0); matrix.transposem(mnormalmatrix, 0, mnormalmatrix, 0); 

before passing shaders:

/*vertex shader*/ attribute vec3 vposition;  attribute vec3 vnormal;  uniform mat4 modelviewmatrix;  uniform mat4 mmvpmatrix; uniform mat4 mviewmatrix; uniform mat4 normalmatrix; uniform float lightingenabled;  varying float lightsenabled; varying vec3 lightposeye; varying vec3 normaleye;  varying vec3 verteye;  void main() {       /*calculate normal matrix*/     vec4 normal = vec4(vnormal, 0.0);     normaleye = normalize(vec3(normalmatrix * normal));      lightsenabled = lightingenabled;      lightposeye = vec3(mviewmatrix * vec4(0.0, 0.0, 3.0, 1.0));      verteye = vec3(modelviewmatrix * vec4(vposition, 1.0));      gl_position = mmvpmatrix * vec4(vposition, 1.0); } 

/*fragment shader*/  precision mediump float;  /*uniform vec4 vcolor; */  varying float lightsenabled; varying vec3 lightposeye; varying vec3 normaleye;  varying vec3 verteye;  void main() {       /*light output components*/     vec3 ia;     vec3 id;      /*light source components*/     vec3 la = vec3(0.5);     vec3 ld = vec3(1.0);     /*vec3 ls = vec3(1.0);*/      vec3 ka = vec3(0.3); /*ambient reflectance term*/     vec3 kd = vec3(1.0); /*diffuse term*/      /*ambient light term*/     ia = la * ka;      float dotprod;     vec3 lighttosurface;      if(lightsenabled > 0.5){         /*diffuse light term*/         lighttosurface = normalize(lightposeye - verteye);          dotprod = dot(lighttosurface, normaleye);         dotprod = max(dotprod, 0.0);     }     else {         dotprod = 1.0;     }      id = ld * kd * dotprod;       gl_fragcolor = vec4(ia + id, 1.0);  } 

i know been while, i've found solution. problem line in vertex shader:

normaleye = normalize(vec3(normalmatrix * normal)); 

i changed to:

normaleye = normalize(vec3(modelviewmatrix * normal)); 

and works fine. although have no idea why second line works when first 1 should.