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/*
* ExpansionPolicy.cpp
* Dasher
*
* Created by Alan Lawrence on 26/10/2009.
* Copyright 2009 Cavendish Laboratory. All rights reserved.
*
*/
#include "ExpansionPolicy.h"
#include "DasherModel.h"
#include <algorithm>
using namespace Dasher;
using namespace std;
void CExpansionPolicy::ExpandNode(CDasherNode *pNode) {
m_pModel->ExpandNode(pNode);
}
bool Less(pair<double,CDasherNode *> x, pair<double, CDasherNode *> y) {return x.first < y.first;}
bool More(pair<double,CDasherNode *> x, pair<double, CDasherNode *> y) {return x.first > y.first;}
BudgettingPolicy::BudgettingPolicy(CDasherModel *pModel, unsigned int iNodeBudget) : CExpansionPolicy(pModel), m_iNodeBudget(iNodeBudget) {}
double BudgettingPolicy::pushNode(CDasherNode *pNode, int iMin, int iMax, bool bExpand, double dParentCost) {
double dRes = getCost(pNode, iMin, iMax);
if (dRes<dParentCost) {
//obvious case: node is less important/costly than parent; will be collapsed first
// (or expanded but only if parent is not collapsed)
vector<pair<double, CDasherNode*> > &target = (bExpand) ? sExpand : sCollapse;
target.push_back(pair<double, CDasherNode *>(dRes,pNode));
} else {
//node has same or greater cost than parent. Take care of latter case...
dRes = dParentCost;
//Parent has children, so must have been enqueued to collapse;
// thus, avoid enqueuing child node to collapse also: if costs are accurate
// (i.e. in terms of the benefit/detriment of what's onscreen), then collapsing
// parent will free up more nodes (by recursively collapsing child)
if (bExpand) sExpand.push_back(pair<double,CDasherNode *>(dRes, pNode));
//Of course, that also removes the possibility of collapsing the parent first,
// then trying to collapse the child afterwards (=>freed pointer), if they get
// sorted the wrong way round...
}
return dRes;
}
///Expand one level per frame; note this won't really take effect until the *next* frame!
bool BudgettingPolicy::apply() {
//firstly, sort the nodes...
sort(sExpand.begin(), sExpand.end(), Less);
//sExpand now in < order: [0] < [1] < ... < [size()-1] - so last element will have highest (cost=)benefit
sort(sCollapse.begin(), sCollapse.end(),More);
//sCollapse now in > order: [0] > ... > [size()-1] - so last element will have lowest cost(=benefit)
//did we expand anything? (if so, there may be more opportunities for expansion next frame)
bool bReturnValue = false;
//maintain record of the highest cost we've incurred by collapsing a node;
// avoid expanding anything LESS beneficial than that, as (even if we've room)
// it'll be better to instead wait until next frame (and possibly re-expand the
// collapsed node! Sadly we can't rely on trading one-for-one as different nodes
// may have different numbers of children...)
double collapseCost = -std::numeric_limits<double>::infinity();
//first, make sure we are within our budget (probably only in case the budget's changed)
while (!sCollapse.empty()
&& currentNumNodeObjects() > m_iNodeBudget)
{
pair<double,CDasherNode *> node = sCollapse.back();
DASHER_ASSERT(node.first >= collapseCost);
collapseCost = node.first;
node.second->Delete_children();
sCollapse.pop_back();
}
//ok, we're now within budget. However, we may still wish to "trade off" nodes
// against each other, in case there are any unimportant (low-cost) nodes we could collapse
// to make room to expand other more important (high-benefit) nodes.
while (!sExpand.empty() && sExpand.back().first > collapseCost)
{
if (currentNumNodeObjects()+sExpand.back().second->ExpectedNumChildren() < m_iNodeBudget)
{
ExpandNode(sExpand.back().second);
sExpand.pop_back();
bReturnValue = true;
//...and loop.
}
else if (!sCollapse.empty()
&& sCollapse.back().first < sExpand.back().first)
{
//could be a beneficial trade - make room by performing collapse...
pair<double,CDasherNode *> node = sCollapse.back();
DASHER_ASSERT(node.first >= collapseCost);
collapseCost = node.first;
node.second->Delete_children();
sCollapse.pop_back();
//...and see how much room that makes
}
else break; //not enough room, nothing to collapse.
}
sExpand.clear();
sCollapse.clear();
return bReturnValue;
}
int BudgettingPolicy::getRange(int y1, int y2, int iMin, int iMax) {
if (y1>iMax || y2 < iMin) return 0;
return min(y2, iMax) - max(y1, iMin);
}
double BudgettingPolicy::getCost(CDasherNode *pNode, int iDasherMinY, int iDasherMaxY) {
return getRange(iDasherMinY, iDasherMaxY, 0, 4096);
}
AmortizedPolicy::AmortizedPolicy(CDasherModel *pModel, unsigned int iNodeBudget) : BudgettingPolicy(pModel,iNodeBudget), m_iMaxExpands(std::max(1u,(500+iNodeBudget)/1000)) {}
AmortizedPolicy::AmortizedPolicy(CDasherModel *pModel, unsigned int iNodeBudget, unsigned int iMaxExpands) : BudgettingPolicy(pModel, iNodeBudget), m_iMaxExpands(iMaxExpands) {}
double AmortizedPolicy::pushNode(CDasherNode *node, int iMin, int iMax, bool bExpand, double dParentCost) {
double dRes = BudgettingPolicy::pushNode(node,iMin,iMax,bExpand,dParentCost);
if (bExpand && sExpand.size() > 2*m_iMaxExpands) trim();
return dRes;
}
bool AmortizedPolicy::apply() {
trim();
return BudgettingPolicy::apply();
}
void AmortizedPolicy::trim() {
if (sExpand.size() <= m_iMaxExpands) return;
//ok - repeatedly find a pivot element, and place it dividing all elements into
//those more than it (in lower indices) and those less than it (in higher indices),
// until we have separated off the <m_iMaxExpands> elements with greatest benefit
#ifdef DEBUG_TRIM
vector<pair<double,CDasherNode *> > backup = sExpand; //yep, copy the lot
#endif
unsigned int start = 0, stop = sExpand.size()-1;
while (true) {
//at this point, we assume we know only that elements [start - stop] need examining....
unsigned int low = start, high = stop;
pair<double,CDasherNode *> &pivot = sExpand[low++];
while (true) {
while (low <= high && !Less(sExpand[low],pivot)) low++;
//all elements (start-low) can stay on left of pivot.
if (low <= high) {
//element <low> needs to be on R of pivot.
while (high >= low && !More(sExpand[high],pivot)) high--;
if (high >= low) {
//element <high> needs to be on L of pivot
pair<double,CDasherNode *> temp = sExpand[low];
sExpand[low++] = sExpand[high];
sExpand[high--]=temp;
continue;
} //else, fall through to break -> place pivot
}
break;
}
//place pivot at index (low-1) - if that's not where it is already!
low--;
if (start!=low) {
pair<double,CDasherNode *> temp = sExpand[start];
sExpand[start]=sExpand[low];
sExpand[low] = temp;
}
//if (low == m_iMaxExpands), elements [0 - low-1] are all <= pivot
//if (low == m_iMaxExpands-1), elements [0 - low] are all <= pivot (as pivot<=pivot!)
//finish in both cases.
if (low < m_iMaxExpands-1)
start=low+1;
else if (low>m_iMaxExpands)
stop=low-1;
else break;
}
//truncate array
sExpand.resize(m_iMaxExpands);
#ifdef DEBUG_TRIM
//now compare with the brute-force method...
sort(sExpand.begin(), sExpand.end(), Less);
sort(backup.begin(), backup.end(), Less);
backup.erase(backup.begin(), backup.end()-m_iMaxExpands);
//now compare. note we _don't_ require the node pointers to be the same;
// where the cut-off point falls within a group of nodes with the same cost,
// the two vectors could have different nodes from that group.
double dFirstCost = sExpand[sExpand.size()-1].first;
for (vector<pair<double, CDasherNode *> >::iterator it1=sExpand.begin(), it2=backup.begin(); it1!=sExpand.end(); it1++, it2++)
if (*it1 == *it2) continue;
else if (it1->first == dFirstCost && it2->first==dFirstCost) continue;
else cout << "trim not equal!\n";
#endif
}
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