Implement scalar multiplier of normal texture.

[SamuelTallet]

Hello @pissang,

I added support of glTF normal scale.
I hope did it correctly ;) Let me know.

Kind regards,
Samuel Tallet-Sabathé

[pissang]

@SamuelTS Thanks for the contribution!! GLSL code needs to be tweaked a bit. Applying normalScale should be done before multiplying tbn.

N = (normalTexel * 2.0 - 1.0);
// Apply scalar multiplier to normal vector of texture.
N =  normalize(N * vec3(normalScale, normalScale, 1.0));
tbn[1] = -tbn[1];
N = normalize(tbn * N);

Other modifications look fine to me!

[SamuelTallet]

Thanks for GLSL code tweak, @pissang.
I suppose glsl2js will auto-update JS? :)

[pissang]

@SamuelTS yeah.