src/libvpsc/block.cpp

/*
 * Authors:
 *   Tim Dwyer <tgdwyer@gmail.com>
 *
 * Copyright (C) 2005 Authors
 *
 * Released under GNU LGPL.  Read the file 'COPYING' for more information.
 */
#include <cassert>
#include "pairingheap/PairingHeap.h"
#include "constraint.h"
#include "block.h"
#include "blocks.h"
#ifdef RECTANGLE_OVERLAP_LOGGING
#include <fstream>
using std::ios;
using std::ofstream;
using std::endl;
#endif
using std::vector;

namespace vpsc {
void Block::addVariable(Variable* const v) {
    v->block=this;
    vars->push_back(v);
    weight+=v->weight;
    wposn += v->weight * (v->desiredPosition - v->offset);
    posn=wposn/weight;
}
Block::Block(Variable* const v) {
    timeStamp=0;
    posn=weight=wposn=0;
    in=NULL;
    out=NULL;
    deleted=false;
    vars=new vector<Variable*>;
    if(v!=NULL) {
        v->offset=0;
        addVariable(v);
    }
}

double Block::desiredWeightedPosition() {
    double wp = 0;
    for (Vit v=vars->begin();v!=vars->end();++v) {
        wp += ((*v)->desiredPosition - (*v)->offset) * (*v)->weight;
    }
    return wp;
}
Block::~Block(void)
{
    delete vars;
    delete in;
    delete out;
}
void Block::setUpInConstraints() {
    setUpConstraintHeap(in,true);
}
void Block::setUpOutConstraints() {
    setUpConstraintHeap(out,false);
}
void Block::setUpConstraintHeap(PairingHeap<Constraint*>* &h,bool in) {
    delete h;
    h = new PairingHeap<Constraint*>(&compareConstraints);
    for (Vit i=vars->begin();i!=vars->end();++i) {
        Variable *v=*i;
        vector<Constraint*> *cs=in?&(v->in):&(v->out);
        for (Cit j=cs->begin();j!=cs->end();++j) {
            Constraint *c=*j;
            c->timeStamp=blockTimeCtr;
            if ((c->left->block != this && in) || (c->right->block != this && !in)) {
                h->insert(c);
            }
        }
    }
}
void Block::merge(Block* b, Constraint* c) {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"  merging on: "<<*c<<",c->left->offset="<<c->left->offset<<",c->right->offset="<<c->right->offset<<endl;
#endif
    double dist = c->right->offset - c->left->offset - c->gap;
    Block *l=c->left->block;
    Block *r=c->right->block;
    if (vars->size() < b->vars->size()) {
        r->merge(l,c,dist);
    } else {
            l->merge(r,c,-dist);
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  merged block="<<(b->deleted?*this:*b)<<endl;
#endif
}

void Block::merge(Block *b, Constraint *c, double dist) {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"    merging: "<<*b<<"dist="<<dist<<endl;
#endif
    c->active=true;
    wposn+=b->wposn-dist*b->weight;
    weight+=b->weight;
    posn=wposn/weight;
    for(Vit i=b->vars->begin();i!=b->vars->end();++i) {
        Variable *v=*i;
        v->block=this;
        v->offset+=dist;
        vars->push_back(v);
    }
    b->deleted=true;
}

void Block::mergeIn(Block *b) {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"  merging constraint heaps... "<<endl;
#endif
    // We check the top of the heaps to remove possible internal constraints
    findMinInConstraint();
    b->findMinInConstraint();
    in->merge(b->in);
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  merged heap: "<<*in<<endl;
#endif
}
void Block::mergeOut(Block *b) {
    findMinOutConstraint();
    b->findMinOutConstraint();
    out->merge(b->out);
}
Constraint *Block::findMinInConstraint() {
    Constraint *v = NULL;
    vector<Constraint*> outOfDate;
    while (!in->isEmpty()) {
        v = in->findMin();
        Block *lb=v->left->block;
        Block *rb=v->right->block;
        // rb may not be this if called between merge and mergeIn
#ifdef RECTANGLE_OVERLAP_LOGGING
        ofstream f(LOGFILE,ios::app);
        f<<"  checking constraint ... "<<*v;
        f<<"    timestamps: left="<<lb->timeStamp<<" right="<<rb->timeStamp<<" constraint="<<v->timeStamp<<endl;
#endif
        if(lb == rb) {
            // constraint has been merged into the same block
#ifdef RECTANGLE_OVERLAP_LOGGING
            if(v->slack()<0) {
                f<<"  violated internal constraint found! "<<*v<<endl;
                f<<"     lb="<<*lb<<endl;
                f<<"     rb="<<*rb<<endl;
            }
#endif
            in->deleteMin();
#ifdef RECTANGLE_OVERLAP_LOGGING
            f<<" ... skipping internal constraint"<<endl;
#endif
        } else if(v->timeStamp < lb->timeStamp) {
            // block at other end of constraint has been moved since this
            in->deleteMin();
            outOfDate.push_back(v);
#ifdef RECTANGLE_OVERLAP_LOGGING
            f<<"    reinserting out of date (reinsert later)"<<endl;
#endif
        } else {
            break;
        }
    }
    for(Cit i=outOfDate.begin();i!=outOfDate.end();++i) {
        v=*i;
        v->timeStamp=blockTimeCtr;
        in->insert(v);
    }
    if(in->isEmpty()) {
        v=NULL;
    } else {
        v=in->findMin();
    }
    return v;
}
Constraint *Block::findMinOutConstraint() {
    if(out->isEmpty()) return NULL;
    Constraint *v = out->findMin();
    while (v->left->block == v->right->block) {
        out->deleteMin();
        if(out->isEmpty()) return NULL;
        v = out->findMin();
    }
    return v;
}
void Block::deleteMinInConstraint() {
    in->deleteMin();
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"deleteMinInConstraint... "<<endl;
    f<<"  result: "<<*in<<endl;
#endif
}
void Block::deleteMinOutConstraint() {
    out->deleteMin();
}
inline bool Block::canFollowLeft(Constraint *c, const Variable* const last) {
    return c->left->block==this && c->active && last!=c->left;
}
inline bool Block::canFollowRight(Constraint *c, const Variable* const last) {
    return c->right->block==this && c->active && last!=c->right;
}

// computes the derivative of v and the lagrange multipliers
// of v's out constraints (as the recursive sum of those below.
// Does not backtrack over u.
// also records the constraint with minimum lagrange multiplier
// in min_lm
double Block::compute_dfdv(Variable* const v, Variable* const u,
            Constraint *&min_lm) {
    double dfdv=v->weight*(v->position() - v->desiredPosition);
    for(Cit it=v->out.begin();it!=v->out.end();++it) {
        Constraint *c=*it;
        if(canFollowRight(c,u)) {
            dfdv+=c->lm=compute_dfdv(c->right,v,min_lm);
            if(!c->equality&&(min_lm==NULL||c->lm<min_lm->lm)) min_lm=c;
        }
    }
    for(Cit it=v->in.begin();it!=v->in.end();++it) {
        Constraint *c=*it;
        if(canFollowLeft(c,u)) {
            dfdv-=c->lm=-compute_dfdv(c->left,v,min_lm);
            if(!c->equality&&(min_lm==NULL||c->lm<min_lm->lm)) min_lm=c;
        }
    }
    return dfdv;
}


// computes dfdv for each variable and uses the sum of dfdv on either side of
// the constraint c to compute the lagrangian multiplier lm_c.
// The top level v and r are variables between which we want to find the
// constraint with the smallest lm.
// When we find r we pass NULL to subsequent recursive calls,
// thus r=NULL indicates constraints are not on the shortest path.
// Similarly, m is initially NULL and is only assigned a value if the next
// variable to be visited is r or if a possible min constraint is returned from
// a nested call (rather than NULL).
// Then, the search for the m with minimum lm occurs as we return from
// the recursion (checking only constraints traversed left-to-right
// in order to avoid creating any new violations).
// We also do not consider equality constraints as potential split points
Block::Pair Block::compute_dfdv_between(
        Variable* r, Variable* const v, Variable* const u,
        const Direction dir = NONE, bool changedDirection = false) {
    double dfdv=v->weight*(v->position() - v->desiredPosition);
    Constraint *m=NULL;
    for(Cit it(v->in.begin());it!=v->in.end();++it) {
        Constraint *c=*it;
        if(canFollowLeft(c,u)) {
            if(dir==RIGHT) {
                changedDirection = true;
            }
            if(c->left==r) {
                    r=NULL;
                    if(!c->equality) m=c;
            }
            Pair p=compute_dfdv_between(r,c->left,v,
                    LEFT,changedDirection);
            dfdv -= c->lm = -p.first;
            if(r && p.second)
                m = p.second;
        }
    }
    for(Cit it(v->out.begin());it!=v->out.end();++it) {
        Constraint *c=*it;
        if(canFollowRight(c,u)) {
            if(dir==LEFT) {
                changedDirection = true;
            }
            if(c->right==r) {
                    r=NULL;
                    if(!c->equality) m=c;
            }
            Pair p=compute_dfdv_between(r,c->right,v,
                    RIGHT,changedDirection);
            dfdv += c->lm = p.first;
            if(r && p.second)
                m = changedDirection && !c->equality && c->lm < p.second->lm
                    ? c
                    : p.second;
        }
    }
    return Pair(dfdv,m);
}

// resets LMs for all active constraints to 0 by
// traversing active constraint tree starting from v,
// not back tracking over u
void Block::reset_active_lm(Variable* const v, Variable* const u) {
    for(Cit it=v->out.begin();it!=v->out.end();++it) {
        Constraint *c=*it;
        if(canFollowRight(c,u)) {
            c->lm=0;
            reset_active_lm(c->right,v);
        }
    }
    for(Cit it=v->in.begin();it!=v->in.end();++it) {
        Constraint *c=*it;
        if(canFollowLeft(c,u)) {
            c->lm=0;
            reset_active_lm(c->left,v);
        }
    }
}

Constraint *Block::findMinLM() {
    Constraint *min_lm=NULL;
    reset_active_lm(vars->front(),NULL);
    compute_dfdv(vars->front(),NULL,min_lm);
    return min_lm;
}
Constraint *Block::findMinLMBetween(Variable* const lv, Variable* const rv) {
    Constraint *min_lm=NULL;
    reset_active_lm(vars->front(),NULL);
    min_lm=compute_dfdv_between(rv,lv,NULL).second;
    return min_lm;
}

// populates block b by traversing the active constraint tree adding variables as they're
// visited.  Starts from variable v and does not backtrack over variable u.
void Block::populateSplitBlock(Block *b, Variable* const v, Variable* const u) {
    b->addVariable(v);
    for (Cit c=v->in.begin();c!=v->in.end();++c) {
        if (canFollowLeft(*c,u))
            populateSplitBlock(b, (*c)->left, v);
    }
    for (Cit c=v->out.begin();c!=v->out.end();++c) {
        if (canFollowRight(*c,u))
            populateSplitBlock(b, (*c)->right, v);
    }
}
// Search active constraint tree from u to see if there is a directed path to v.
// Returns true if path is found with all constraints in path having their visited flag
// set true.
bool Block::isActiveDirectedPathBetween(Variable* u, Variable *v) {
    if(u==v) return true;
    for (Cit c=u->out.begin();c!=u->out.end();++c) {
        if(canFollowRight(*c,NULL)) {
            if(isActiveDirectedPathBetween((*c)->right,v)) {
                (*c)->visited=true;
                return true;
            }
            (*c)->visited=false;
        }
    }
    return false;
}

Constraint* Block::splitBetween(Variable* const vl, Variable* const vr,
            Block* &lb, Block* &rb) {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"  need to split between: "<<*vl<<" and "<<*vr<<endl;
#endif
    Constraint *c=findMinLMBetween(vl, vr);
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  going to split on: "<<*c<<endl;
#endif
    split(lb,rb,c);
    deleted = true;
    return c;
}

void Block::split(Block* &l, Block* &r, Constraint* c) {
    c->active=false;
    l=new Block();
    populateSplitBlock(l,c->left,c->right);
    r=new Block();
    populateSplitBlock(r,c->right,c->left);
}

double Block::cost() {
    double c = 0;
    for (Vit v=vars->begin();v!=vars->end();++v) {
        double diff = (*v)->position() - (*v)->desiredPosition;
        c += (*v)->weight * diff * diff;
    }
    return c;
}
ostream& operator <<(ostream &os, const Block& b)
{
    os<<"Block:";
    for(Block::Vit v=b.vars->begin();v!=b.vars->end();++v) {
        os<<" "<<**v;
    }
    if(b.deleted) {
        os<<" Deleted!";
    }
    return os;
}
}