Spherical Harmonics compute optimization

[GuoLei1990]

Our Spherical Harmonics compute in Shader can optimization.

We can check this :http://www.fractalforums.com/programming/shader-function-or-instruction-cost-(performance)/

How to say: many engine get irradiance use the func like this:

mediump vec3 shEvalLinearL0L1(mediump vec4 normal)
{
mediump vec3 x;
// Linear (L1) + constant (L0) polynomial terms
x.r = dot(u_AmbientSHAr, normal);
x.g = dot(u_AmbientSHAg, normal);
x.b = dot(u_AmbientSHAb, normal);
return x;
}

mediump vec3 shEvalLinearL2(mediump vec4 normal)
{
	mediump vec3 x1,x2;
	// 4 of the quadratic (L2) polynomials
	mediump vec4 vB = normal.xyzz * normal.yzzx;
	x1.r = dot(u_AmbientSHBr, vB);
	x1.g = dot(u_AmbientSHBg, vB);
	x1.b = dot(u_AmbientSHBb, vB);

	// Final (5th) quadratic (L2) polynomial
	mediump float vC = normal.x*normal.x - normal.y*normal.y;
	x2 = u_AmbientSHC.rgb * vC;

	return x1 + x2;
}

Because dot cost only 3 cycles in GPU, so is faster, If you do this you must do some modifies before Incoming shader.