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// Author: Philippe Ivaldi
// http://www.piprime.fr/
// Based on this paper:
// http://www.cs.hku.hk/research/techreps/document/TR-2007-07.pdf
// Note: the additional rotation for a cyclic smooth spine curve is not
// yet properly determined.
// TODO: Implement variational principles for RMF with boundary conditions:
// minimum total angular speed OR minimum total squared angular speed
import three;
real tubegranularity=1e-7;
void render(path3 s, real r, void f(path3, real))
{
void Split(triple z0, triple c0, triple c1, triple z1, real t0=0, real t1=1,
real depth=mantissaBits) {
if(depth > 0) {
real S=straightness(z0,c0,c1,z1);
if(S > max(tubegranularity*max(abs(z0),abs(c0),abs(c1),abs(z1)))) {
--depth;
triple m0=0.5*(z0+c0);
triple m1=0.5*(c0+c1);
triple m2=0.5*(c1+z1);
triple m3=0.5*(m0+m1);
triple m4=0.5*(m1+m2);
triple m5=0.5*(m3+m4);
real tm=0.5*(t0+t1);
Split(z0,m0,m3,m5,t0,tm,depth);
Split(m5,m4,m2,z1,tm,t1,depth);
return;
}
}
f(z0..controls c0 and c1..z1,t0);
}
Split(point(s,0),postcontrol(s,0),precontrol(s,1),point(s,1));
}
// A 3D version of roundedpath(path, real).
path3 roundedpath(path3 A, real r)
{
// Author of this routine: Jens Schwaiger
guide3 rounded;
triple before, after, indir, outdir;
int len=length(A);
bool cyclic=cyclic(A);
if(len < 2) {return A;};
if(cyclic) {rounded=point(point(A,0)--point(A,1),r);}
else {rounded=point(A,0);}
for(int i=1; i < len; i=i+1) {
before=point(point(A,i)--point(A,i-1),r);
after=point(point(A,i)--point(A,i+1),r);
indir=dir(point(A,i-1)--point(A,i),1);
outdir=dir(point(A,i)--point(A,i+1),1);
rounded=rounded--before{indir}..{outdir}after;
}
if(cyclic) {
before=point(point(A,0)--point(A,len-1),r);
indir=dir(point(A,len-1)--point(A,0),1);
outdir=dir(point(A,0)--point(A,1),1);
rounded=rounded--before{indir}..{outdir}cycle;
} else rounded=rounded--point(A,len);
return rounded;
}
real[] sample(path3 g, real r, real relstep=0)
{
real[] t;
int n=length(g);
if(relstep <= 0) {
for(int i=0; i < n; ++i)
render(subpath(g,i,i+1),r,new void(path3, real s) {t.push(i+s);});
t.push(n);
} else {
int nb=ceil(1/relstep);
relstep=n/nb;
for(int i=0; i <= nb; ++i)
t.push(i*relstep);
}
return t;
}
real degrees(rmf a, rmf b)
{
real d=degrees(acos1(dot(a.r,b.r)));
real dt=dot(cross(a.r,b.r),a.t);
d=dt > 0 ? d : 360-d;
return d%360;
}
restricted int coloredNodes=1;
restricted int coloredSegments=2;
struct coloredpath
{
path p;
pen[] pens(real);
bool usepens=false;
int colortype=coloredSegments;
void operator init(path p, pen[] pens=new pen[] {currentpen},
int colortype=coloredSegments)
{
this.p=p;
this.pens=new pen[] (real t) {return pens;};
this.usepens=true;
this.colortype=colortype;
}
void operator init(path p, pen[] pens(real), int colortype=coloredSegments)
{
this.p=p;
this.pens=pens;
this.usepens=true;
this.colortype=colortype;
}
void operator init(path p, pen pen(real))
{
this.p=p;
this.pens=new pen[] (real t) {return new pen[] {pen(t)};};
this.usepens=true;
this.colortype=coloredSegments;
}
}
coloredpath operator cast(path p)
{
coloredpath cp=coloredpath(p);
cp.usepens=false;
return cp;
}
coloredpath operator cast(guide p)
{
return coloredpath(p);
}
private surface surface(rmf[] R, real[] t, coloredpath cp, transform T(real),
bool cyclic)
{
path g=cp.p;
int l=length(g);
bool[] planar;
for(int i=0; i < l; ++i)
planar[i]=straight(g,i);
surface s;
path3 sec=path3(T(t[0]/l)*g);
real adjust=0;
if(cyclic) adjust=-degrees(R[0],R[R.length-1])/(R.length-1);
path3 sec1=shift(R[0].p)*transform3(R[0].r,R[0].s,R[0].t)*sec,
sec2;
for(int i=1; i < R.length; ++i) {
sec=path3(T(t[i]/l)*g);
sec2=shift(R[i].p)*transform3(R[i].r,cross(R[i].t,R[i].r),R[i].t)*
rotate(i*adjust,Z)*sec;
for(int j=0; j < l; ++j) {
surface st=surface(subpath(sec1,j,j+1)--subpath(sec2,j+1,j)--cycle,
planar=planar[j]);
if(cp.usepens) {
pen[] tp1=cp.pens(t[i-1]/l), tp2=cp.pens(t[i]/l);
tp1.cyclic=true; tp2.cyclic=true;
if(cp.colortype == coloredSegments) {
st.colors(new pen[][] {{tp1[j],tp1[j],tp2[j],tp2[j]}});
} else {
st.colors(new pen[][] {{tp1[j],tp1[j+1],tp2[j+1],tp2[j]}});
}
}
s.append(st);
}
sec1=sec2;
}
return s;
}
surface tube(path3 g, coloredpath section,
transform T(real)=new transform(real t) {return identity();},
real corner=1, real relstep=0)
{
pair M=max(section.p), m=min(section.p);
real[] t=sample(g,max(M.x-m.x,M.y-m.y)/max(realEpsilon,abs(corner)),
min(abs(relstep),1));
bool cyclic=cyclic(g);
t.cyclic=cyclic;
return surface(rmf(g,t),t,section,T,cyclic);
}
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