[VERT]

attribute vec4 a_position;

varying vec3 texCoord;

uniform mat4 u_worldTrans;
uniform mat4 u_projTrans;
...

void main()
{
   gl_Position = u_projTrans * u_worldTrans * a_position;
   texCoord = vec3(a_position);
}


[FRAG]
varying vec3 texCoord;
uniform samplerCube u_cubemapTex;

void main()
{
  gl_FragColor = textureCube(u_cubemapTex, texCoord);
}

[VERT]
attribute vec3 a_normal;

varying vec3 v_reflection;

uniform mat4 u_matViewInverseTranspose;
uniform vec3 u_cameraPos;
...

void main()
{
   mat3 normalMatrix = mat3(u_matViewInverseTranspose);
   vec3 n = normalize(normalMatrix * a_normal);

   //calculate reflection
   vec3 vView = a_position.xyz - u_cameraPos.xyz;
   v_reflection = reflect(vView, n);

   ...
}