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#include <queue>

#include <iostream>

#include "quadric_simplify.h"

#include "smooth.h"

#include "HMesh/VertexCirculator.h"

#include "Geometry/QEM.h"

namespace HMesh

{

	using namespace CGLA;

	using namespace std;

	using namespace GEO;

	using namespace HMesh;

	namespace

	{

		/* We create a record for each halfedge where we can keep its time

		stamp. If the time stamp on the halfedge record is bigger than

		the stamp on the simplification record, we cannot use the 

		simplification record (see below). */

		struct HalfEdgeRec

				{

					HalfEdgeIter he;

					int time_stamp;

					void halfedge_removed() {time_stamp = -1;}

					HalfEdgeRec(): time_stamp(0) {}

				};

		/* The simpliciation record contains information about a potential

		edge contraction */

		struct SimplifyRec

		{

			Vec3d opt_pos;  // optimal vertex position

			int he_index;   // Index (into HalfEdgeRec vector) of edge

							// we want to contract

			float err;      // Error associated with contraction

			int time_stamp; // Time stamp (see comment on HalfEdgeRec)

			int visits;     // Visits (number of times we considered this 

							// record).

		};

		bool operator<(const SimplifyRec& s1, const SimplifyRec& s2)

		{

			return s1.err > s2.err;

		}

		class QuadricSimplifier

		{

			typedef priority_queue<SimplifyRec> SimplifyQueue;

			typedef vector<QEM> QEMVec;

			typedef vector<HalfEdgeRec> HalfEdgeVec;

			Manifold& m;

			HalfEdgeVec halfedge_vec;

			QEMVec qem_vec;

			SimplifyQueue sim_queue;

			double singular_thresh;

			bool choose_optimal_positions;

			/* Compute the error associated with contraction of he and the

				optimal position of resulting vertex. */

			void push_simplify_rec(HalfEdgeIter he);

			/* Check whether the contraction is valid. See below for details*/

			bool check_consistency(HalfEdgeIter he, const Vec3d& opt_pos);

			/* Update the time stamp of a halfedge. A halfedge and its opp edge

				may have different stamps. We choose a stamp that is greater

				than either and assign to both.*/

			void update_time_stamp(HalfEdgeIter he)

			{

				int time_stamp = s_max(halfedge_vec[he->touched].time_stamp,

									   halfedge_vec[he->opp->touched].time_stamp);

				time_stamp++;

				halfedge_vec[he->touched].time_stamp = time_stamp;

				halfedge_vec[he->opp->touched].time_stamp = time_stamp;

			}

			/* Update time stamps for all halfedges in one ring of vi */

			void update_onering_timestamp(VertexIter vi);

			/* Perform a collapse - if conditions are met. Returns 1 or 0 

				accordingly. */

			int collapse(SimplifyRec& simplify_rec);

		public:

				/* Create a simplifier for a manifold */

				QuadricSimplifier(Manifold& _m, double _singular_thresh, bool _choose_optimal_positions): 

				m(_m), 

				halfedge_vec(m.no_halfedges()), 

				qem_vec(m.no_vertices()),

				singular_thresh(_singular_thresh),

				choose_optimal_positions(_choose_optimal_positions)

			{

					// Enumerate vertices

					m.enumerate_vertices();

					// Enumerate halfedges

					m.enumerate_halfedges();

			}

			/* Simplify doing at most max_work contractions */

			void reduce(int max_work);

		};

		bool QuadricSimplifier::check_consistency(HalfEdgeIter he, 

												  const Vec3d& opt_pos)

		{

			VertexIter v0 = he->vert;

			VertexIter v1 = he->opp->vert;

			Vec3d p0(v0->pos);

			/* This test is inspired by Garland's Ph.D. thesis. We try

				to detect whether flipped triangles will occur by sort of

				ensuring that the new vertex is in the hull of the one rings

				of the vertices at either end of the edge being contracted 

				I also had an additional check intended to ensure that poor valencies

				would not be introduced, but it seemed to be unnecessary.

				*/

			for(VertexCirculator vc(v0); !vc.end(); ++vc)

			{

				HalfEdgeIter h = vc.get_halfedge();

				if(h->vert != v1 && h->next->vert != v1)

				{

					Vec3d pa(h->vert->pos);

					Vec3d pb(h->next->vert->pos);

					Vec3d dir = normalize(pb-pa);

					Vec3d n = p0 - pa;

					n = n - dir * dot(dir,n);

					if(dot(n,opt_pos - pa) <= 0)

						return false;

				}

			}

			return true;

		}

		void QuadricSimplifier::push_simplify_rec(HalfEdgeIter he)

		{

			// Get QEM for both end points

			const QEM& Q1 = qem_vec[he->vert->touched];

			const QEM& Q2 = qem_vec[he->opp->vert->touched];

			QEM q = Q1;

			q += Q2;

			float err;

			Vec3d opt_pos(0);

			Vec3d opt_origin = Vec3d(he->vert->pos+he->opp->vert->pos)/2.0;

			if(choose_optimal_positions)

				opt_pos = q.opt_pos(singular_thresh,opt_origin);

			else

			{

				Vec3d p1(he->vert->pos), p2(he->opp->vert->pos);

				float err1 = q.error(p1);

				float err2 = q.error(p2);

				if(err1<err2) 

				{

					err = err1;

					opt_pos = p1;

				}

				else

				{

					err = err2;

					opt_pos = p2;				

				}

			}

			err = q.error(opt_pos);

			// Create SimplifyRec

			int he_index = he->touched;

			SimplifyRec simplify_rec;

			simplify_rec.opt_pos = opt_pos;

			simplify_rec.err = err;

			simplify_rec.he_index = he_index;

			simplify_rec.time_stamp = halfedge_vec[he->touched].time_stamp;

			simplify_rec.visits = 0;

			// push it.

			sim_queue.push(simplify_rec);

		}

		void QuadricSimplifier::update_onering_timestamp(VertexIter vi)

		{

			// For all emanating edges he

			for(VertexCirculator vc(vi);

				!vc.end(); ++vc)

			{

				HalfEdgeIter he = vc.get_halfedge();

				update_time_stamp(he);

				push_simplify_rec(he);

			}

		}

		int QuadricSimplifier::collapse(SimplifyRec& simplify_rec)

		{

			int he_index = simplify_rec.he_index;

			HalfEdgeIter he = halfedge_vec[he_index].he;

			// Check the time stamp to verify that the simplification 

			// record is the newest. If the halfedge has been removed

			// the time stamp is -1 and the comparison will also fail.

			if(halfedge_vec[he_index].time_stamp == simplify_rec.time_stamp)

			{

				VertexIter v = he->opp->vert;

				VertexIter n = he->vert;

				// If the edge is, in fact, collapsible

				if(m.collapse_precond(he))

				{

					// If our consistency checks pass, we are relatively

					// sure that the contraction does not lead to a face flip.

					if(check_consistency(he, simplify_rec.opt_pos) && 

					   check_consistency(he->opp, simplify_rec.opt_pos))

					{

						// Get QEM for both end points

						const QEM& Q1 = qem_vec[he->vert->touched];

						const QEM& Q2 = qem_vec[he->opp->vert->touched];

						// Compute Q_new = Q_1 + Q_2

						QEM q = Q1;

						q += Q2;

						// Mark all halfedges that will be removed as dead

						halfedge_vec[he->touched].halfedge_removed();

						halfedge_vec[he->opp->touched].halfedge_removed();

						if(he->next->next->next == he)

						{

							halfedge_vec[he->next->touched].halfedge_removed();

							halfedge_vec[he->next->next->touched].halfedge_removed();

						}

						if(he->opp->next->next->next == he->opp)

						{

							halfedge_vec[he->opp->next->touched].halfedge_removed();

							halfedge_vec[he->opp->next->next->touched].halfedge_removed();

						}

						// Do collapse

						m.collapse_halfedge(he,false);

						n->pos = Vec3f(simplify_rec.opt_pos);

						qem_vec[n->touched] = q;

						update_onering_timestamp(n);

						return 1;

					}

				}

				// If we are here, the collapse was not allowed. If we have

				// seen this simplify record less than 100 times, we try to

				// increase the error and store the record again. Maybe some

				// other contractions will make it more digestible later.

				if(simplify_rec.visits < 100)

				{

					simplify_rec.err *= 1.01f;

					++simplify_rec.visits;

					sim_queue.push(simplify_rec);

				}

			}

			return 0;

		}

		void QuadricSimplifier::reduce(int max_work)

		{

			// Set t = 0 for all halfedges

			int i=0;

			for(HalfEdgeIter he = m.halfedges_begin();

				he != m.halfedges_end(); ++he, ++i)

				halfedge_vec[i].he = he;

			cout << "Computing quadrics" << endl;

			// For all vertices, compute quadric and store in qem_vec

			for(VertexIter vi=m.vertices_begin(); vi != m.vertices_end(); ++vi)

			{

				Vec3d p(vi->pos);

				Vec3d vn(normal(vi));

				QEM q;

				for(VertexCirculator vc(vi); !vc.end(); ++vc)

				{

					FaceIter f = vc.get_face();

					if(f != NULL_FACE_ITER)

					{

						Vec3d n(normal(f));

						double a = area(f);

						q += QEM(p, n, a / 3.0);

					}

					if ((f == NULL_FACE_ITER || 

						vc.get_opp_halfedge()->face ==  NULL_FACE_ITER) && sqr_length(vn) > 0.0)

					{

						Vec3d edge = Vec3d(vc.get_halfedge()->vert->pos)-p;

						double edge_len = sqr_length(edge); 

						if(edge_len > 0.0)

							{

								Vec3d n = cross(vn, edge);

								q += QEM(p, n, 2*edge_len);

							}

					}

				}

				qem_vec[vi->touched] = q;

			}

			cout << "Pushing initial halfedges" << endl;

			for(HalfEdgeIter he = m.halfedges_begin();

				he != m.halfedges_end(); ++he)

				// For all halfedges, 

			{

				if(halfedge_vec[he->touched].time_stamp == 0)

				{

					update_time_stamp(he);

					push_simplify_rec(he);

				}

			}

			cout << "Simplify" << endl;

			int work = 0;

			while(!sim_queue.empty() && work < max_work)

			{

				SimplifyRec simplify_record = sim_queue.top();

				sim_queue.pop();

				work += 2*collapse(simplify_record);

				if((work % 100) == 0)

				{

					cout << "work = " << work << endl;

					cout << "sim Q size = " << sim_queue.size() << endl;

				}

			}

		}

	}

	void quadric_simplify(Manifold& m, double keep_fraction, double singular_thresh, bool choose_optimal_positions)

	{

		gel_srand(1210);

		int F = m.no_faces();

		int max_work = max(0, F- static_cast<int>(keep_fraction * F));

		QuadricSimplifier qsim(m, singular_thresh, choose_optimal_positions);

		qsim.reduce(max_work);

	}

}