`trilinear_interp` is inconsistent between listings and src

[rjkilpatrick]

When we are introduced to trilinear_interp, it is a function outside of the perlin class (listing 33):

raytracing.github.io/books/RayTracingTheNextWeek.html

Lines 1597 to 1611 in 80a955b

	inline double trilinear_interp(double c[2][2][2], double u, double v, double w) {
	auto accum = 0.0;
	for (int i=0; i < 2; i++)
	for (int j=0; j < 2; j++)
	for (int k=0; k < 2; k++)
	accum += (i*u + (1-i)*(1-u))*
	(j*v + (1-j)*(1-v))*
	(k*w + (1-k)*(1-w))*c[i][j][k];
	return accum;
	}
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
	class perlin {

However, when later amended (listing 39), it is moved into the class and marked with const (only valid for class member functions).

raytracing.github.io/books/RayTracingTheNextWeek.html

Lines 1842 to 1865 in 80a955b

	class perlin {
	...
	private:
	...
	inline double perlin_interp(vec3 c[2][2][2], double u, double v, double w) const {
	auto uu = u*u*(3-2*u);
	auto vv = v*v*(3-2*v);
	auto ww = w*w*(3-2*w);
	auto accum = 0.0;
	for (int i=0; i < 2; i++)
	for (int j=0; j < 2; j++)
	for (int k=0; k < 2; k++) {
	vec3 weight_v(u-i, v-j, w-k);
	accum += (i*uu + (1-i)*(1-uu))
	* (j*vv + (1-j)*(1-vv))
	* (k*ww + (1-k)*(1-ww))
	* dot(c[i][j][k], weight_v);
	}
	return accum;
	}
	...
	}

In the src directory, the const is missing but it's given a static

raytracing.github.io/src/common/perlin.h

Lines 100 to 116 in 80a955b

	inline static double perlin_interp(vec3 c[2][2][2], double u, double v, double w) {
	auto uu = u*u*(3-2*u);
	auto vv = v*v*(3-2*v);
	auto ww = w*w*(3-2*w);
	auto accum = 0.0;
	for (int i=0; i < 2; i++)
	for (int j=0; j < 2; j++)
	for (int k=0; k < 2; k++) {
	vec3 weight_v(u-i, v-j, w-k);
	accum += (i*uu + (1-i)*(1-uu))*
	(j*vv + (1-j)*(1-vv))*
	(k*ww + (1-k)*(1-ww))*dot(c[i][j][k], weight_v);
	}
	return accum;
	}

I propose changing listing 33 to a private member function for consistency.

Can someone advise about which function signature (i.e. static and/or const) should be the authoritative version? I can then put a PR together

[hollasch]

Thanks. It should be static; delete the inline keyword.

[hollasch]

Resolved in #724