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he_mesh.cpp
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he_mesh.cpp
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#include "he_mesh.h"
#include <set>
#include <map>
#include <vector>
using namespace std;
template<class T>
struct T2
{
T2(T* _a):x(_a[0]),y(_a[1]){}
T2(T _a1,T _a2):x(_a1),y(_a2){}
T2(T _a1):x(_a1),y(_a1){}
T2():x(0),y(0){}
T2<T> reverse(){return T2(y,x);}
const T2<T> reverse()const{return T2(y,x);}
T2<T>& operator+=(const T2& b)
{
x+=b.x;
y+=b.y;
return *this;
}
bool operator<(const T2& b)const
{
return this->x==b.x?this->y<b.y:this->x<b.x;
}
T x,y;
};
typedef T2<int> int2;
__forceinline float3 get_tangent(const float3& normal)
{
float3 c1 = cross(normal, float3(0.0f, 0.0f, 1.0f));
float3 c2 = cross(normal, float3(0.0f, 1.0f, 0.0f));
return length2(c1) > length2(c2)? c1: c2;
}
// on from's tangent plane
float angle_on_tangent_plane(he_vert* from,he_vert* to)
{
float3 axis=get_tangent(from->normal);
float3 v=to->pos-from->pos;
float a=acosf(dot(normalize(v),axis));
return dot(from->normal,cross(axis,v))>=0.f?
a:2*M_PI-a;
}
struct BoundaryEdge
{
BoundaryEdge(he_edge* e):edge(e),from(0),angle(0.f)
{
if(e)
{
from=e->vert_from;
angle=angle_on_tangent_plane(e->vert_from,e->vert_to);
}
}
he_edge* edge;
he_vert* from;
float angle;
};
struct BoundaryEdgeCMP
{
bool operator()(const BoundaryEdge& first, const BoundaryEdge& second) const
{
// large angle first because we do clockwise searching, find first one that is less than target
return (first.from==second.from?first.angle>second.angle:first.from<second.from);
}
};
bool he_mesh::construct(const MeshData& _mesh)
{
free();
vector<he_vert*> vert_map(_mesh.nverts,0);
map<int2,he_edge*> edge_map;
typedef map<int2,he_edge*>::iterator edge_map_itr;
int* vi=_mesh.vi;
for(int fi=0;fi<_mesh.ntris;++fi,vi+=3)
{
he_face* face=faces.append();
he_edge* _e3[3];
for(int i=0;i<3;++i)
{
if(edge_map[int2(vi[i],vi[(i+1)%3])])
{
printf("error: cannot handle non-manifold edge, aborting\n");
return false;
}
// assume manifold, then he_edge is always created
he_edge* e=edges.append();_e3[i]=e;
if(!face->edge) face->edge=e;
int idx=vi[i];
he_vert* vfrom=vert_map[idx];
if(!vfrom)
{
vfrom=vert_map[idx]=verts.append();
vfrom->id=idx;
vfrom->pos=_mesh.p[idx];
vfrom->normal=_mesh.n[idx];
}
if(!vfrom->edge) vfrom->edge=e; // see !vto
idx=vi[(i+1)%3]; // next
he_vert* vto=vert_map[idx];
if(!vto)
{
vto=vert_map[idx]=verts.append();
vto->id=idx;
vto->pos=_mesh.p[idx];
vto->normal=_mesh.n[idx];
// edge not set
}
e->face=face;
e->vert_from=vfrom;
e->vert_to=vto;
edge_map[int2(vi[i],idx)]=e;
}
_e3[0]->next=_e3[1];
_e3[1]->next=_e3[2];
_e3[2]->next=_e3[0];
_e3[1]->prev=_e3[0];
_e3[2]->prev=_e3[1];
_e3[0]->prev=_e3[2];
}
set<BoundaryEdge,BoundaryEdgeCMP> boundary_edges;
typedef set<BoundaryEdge,BoundaryEdgeCMP>::iterator BEdge_Itr;
// pair the edges
for(edge_map_itr itr=edge_map.begin();itr!=edge_map.end();++itr)
{
if(itr->second) // set to 0
{
edge_map_itr findit=edge_map.find(itr->first.reverse());
if(findit!=edge_map.end())
{
itr->second->pair=findit->second;
findit->second->pair=itr->second;
findit->second=0; // no need to precess when encountered
}
else
{
// add boundary edges
he_edge* bedge=edges.append();
itr->second->pair=bedge;
bedge->pair=itr->second;
bedge->vert_from=vert_map[itr->first.y];
bedge->vert_to=vert_map[itr->first.x];
// no face
// next filled below
boundary_edges.insert(BoundaryEdge(bedge));
}
}
// else its pair already processed
}
// MY algorithm:
// 1. build the b-he map, sort by start point, then by the edge angle
// 2. for each b-he, find all other b-hes that begin with its end point in the map, find the b-he CLOCKWISE
for(BEdge_Itr bitr=boundary_edges.begin();bitr!=boundary_edges.end();++bitr)
{
BoundaryEdge lower_edge(0),upper_edge(0);
// normal range is [0,360]
lower_edge.angle=361.f;
upper_edge.angle=-1.f;
lower_edge.from=bitr->edge->vert_to;
upper_edge.from=bitr->edge->vert_to;
BEdge_Itr itr_begin=boundary_edges.lower_bound(lower_edge),
itr_end=boundary_edges.lower_bound(upper_edge);
if(itr_begin==itr_end)
{
// wtf??? impossible
}
if(std::distance(itr_begin,itr_end)==1) // only one, around corner
{
bitr->edge->next=itr_begin->edge;
itr_begin->edge->prev=bitr->edge;
}
else // face vertices listed in counter-clockwise, search clockwise, find the first edge
{
float cur_angle=angle_on_tangent_plane(bitr->edge->vert_to,bitr->edge->vert_from);
// todo: *(itr_end-1)>cur_angle, then all > cur_angle
BEdge_Itr i=itr_begin;
for(;i!=itr_end;++i)
{
// first <= cur_angle (the largest that <=cur_angle)
if(i->angle<=cur_angle) // == wtf!!
{
break;
}
}
if(i==itr_end) // then it's the first one
i=itr_begin;
bitr->edge->next=i->edge;
i->edge->prev=bitr->edge;
}
}
return true;
}
bool he_mesh::dumpOFF(const char* fpath)
{
FILE* fp=fopen(fpath,"w");
fprintf(fp,"OFF\n");
fprintf(fp,"%d %d %d\n",verts.size(),faces.size(),0/*edges.size()*/);
map<he_vert*,int> vert2id;
int id=0;
for(he_vert* vert=verts.begin();vert;vert=verts.next())
{
fprintf(fp,"%f %f %f\n",vert->pos.x,vert->pos.y,vert->pos.z);
vert2id[vert]=id++;
}
for(he_face* face=faces.begin();face;face=faces.next())
{
fprintf(fp,"3 %d %d %d\n",
vert2id[face->edge->vert_from],
vert2id[face->edge->vert_to],
vert2id[face->edge->next->vert_to]);
}
fclose(fp);
return true;
}