#include <u.h>
#include <libc.h>
#include <geometry.h>

// https://iquilezles.org/articles/distfunctions
double
sdSphere(Point3 p, double r)
{
	return vec3len(p)-r;
}
    
Point3
map(Point3 p, double time)
{
	double d;

	d = sdSphere(p, 0.2);
	return Pt3(d, p.x, p.y, p.z);
}

// https://iquilezles.org/articles/normalsSDF
Point3
calcNormal(Point3 pos, double time)
{
	Point3 n, e, e₂;
	int i;

	n = Vec3(0,0,0);
	for(i = 0; i < 4; i++){
		e = Vec3((((i+3)>>1)&1),((i>>1)&1),(i&1));
		e = mulpt3(subpt3(mulpt3(e, 2), Vec3(1,1,1)), 0.5773);
		e₂ = mulpt3(e, 0.0005);
		n = addpt3(n, mulpt3(e, map(addpt3(pos, e₂), time).x));
	}
	return normvec3(n);
}

void
main(int, char **)
{
	Point3 p, n;

	p = Pt3(0,1,1,1);
	n = calcNormal(p, 0);
	exits(nil);
}