interface/layouter/ComplexLayouter.cpp

/*
 * Copyright 2007, Ingo Weinhold <bonefish@cs.tu-berlin.de>.
 * All rights reserved. Distributed under the terms of the MIT License.
 */

#include "ComplexLayouter.h"

#include <math.h>
#include <stdio.h>
#include <string.h>

#include <new>

#include <OS.h>
#include <Size.h>

#include <AutoDeleter.h>

#include "LayoutOptimizer.h"
#include "SimpleLayouter.h"


//#define TRACE_COMPLEX_LAYOUTER	1
#if TRACE_COMPLEX_LAYOUTER
#	define TRACE(format...)	printf(format);
#	define TRACE_ONLY(x)	x
#else
#	define TRACE(format...)
#	define TRACE_ONLY(x)
#endif

using std::nothrow;


// MyLayoutInfo
class ComplexLayouter::MyLayoutInfo : public LayoutInfo {
public:
	MyLayoutInfo(int32 elementCount, int32 spacing)
		: fCount(elementCount),
		  fSpacing(spacing)
	{
		// We also store the location of the virtual elementCountth element.
		// Thus fLocation[i + 1] - fLocation[i] is the size of the ith element
		// (not considering spacing).
		fLocations = new(nothrow) int32[elementCount + 1];
	}

	~MyLayoutInfo()
	{
		delete[] fLocations;
	}

	void InitFromSizes(int32* sizes)
	{
		fLocations[0] = 0;
		for (int32 i = 0; i < fCount; i++)
			fLocations[i + 1] = fLocations[i] + sizes[i] + fSpacing;
	}

	virtual float ElementLocation(int32 element)
	{
		if (element < 0 || element >= fCount)
			return 0;

		return fLocations[element];
	}

	virtual float ElementSize(int32 element)
	{
		if (element < 0 || element >= fCount)
			return -1;

		return fLocations[element + 1] - fLocations[element] - 1
			- fSpacing;
	}

	virtual float ElementRangeSize(int32 position, int32 length)
	{
		if (position < 0 || length < 0 || position + length > fCount)
			return -1;

		return fLocations[position + length] - fLocations[position] - 1
			- fSpacing;
	}

	void Dump()
	{
		printf("ComplexLayouter::MyLayoutInfo(): %" B_PRId32 " elements:\n",
			fCount);
		for (int32 i = 0; i < fCount + 1; i++) {
			printf("  %2" B_PRId32 ": location: %4" B_PRId32 "\n", i,
				fLocations[i]);
		}
	}

public:
	int32	fCount;
	int32	fSpacing;
	int32*	fLocations;
};


// Constraint
struct ComplexLayouter::Constraint {
	Constraint(int32 start, int32 end, int32 min, int32 max)
		: start(start),
		  end(end),
		  min(min),
		  max(max),
		  next(NULL)
	{
		if (min > max)
			max = min;
		effectiveMax = max;
	}

	void Restrict(int32 newMin, int32 newMax)
	{
		if (newMin > min)
			min = newMin;
		if (newMax < max)
			max = newMax;
		if (min > max)
			max = min;
		effectiveMax = max;
	}

	bool IsSatisfied(int32* sumValues) const
	{
		int32 value = sumValues[end] - sumValues[start - 1];
		return (value >= min && value <= max);
	}

	int32		start;
	int32		end;
	int32		min;
	int32		max;
	int32		effectiveMax;
	Constraint*	next;
};


// SumItem
struct ComplexLayouter::SumItem {
	int32	min;
	int32	max;
	bool	minDirty;
	bool	maxDirty;
};


// SumItemBackup
struct ComplexLayouter::SumItemBackup {
	int32	min;
	int32	max;
};


// #pragma mark - ComplexLayouter


// constructor
ComplexLayouter::ComplexLayouter(int32 elementCount, float spacing)
	: fElementCount(elementCount),
	  fSpacing((int32)spacing),
	  fConstraints(new(nothrow) Constraint*[elementCount]),
	  fWeights(new(nothrow) float[elementCount]),
	  fSums(new(nothrow) SumItem[elementCount + 1]),
	  fSumBackups(new(nothrow) SumItemBackup[elementCount + 1]),
	  fOptimizer(new(nothrow) LayoutOptimizer(elementCount)),
	  fUnlimited((int32)B_SIZE_UNLIMITED / (elementCount == 0 ? 1 : elementCount)),
	  fMinMaxValid(false),
	  fOptimizerConstraintsAdded(false)
{
	if (fConstraints)
		memset(fConstraints, 0, sizeof(Constraint*) * fElementCount);

	if (fWeights) {
		for (int32 i = 0; i < fElementCount; i++)
			fWeights[i] = 1.0f;
	}
}


// destructor
ComplexLayouter::~ComplexLayouter()
{
	for (int32 i = 0; i < fElementCount; i++) {
		Constraint* constraint = fConstraints[i];
		fConstraints[i] = NULL;
		while (constraint != NULL) {
			Constraint* next = constraint->next;
			delete constraint;
			constraint = next;
		}
	}

	delete[] fConstraints;
	delete[] fWeights;
	delete[] fSums;
	delete[] fSumBackups;
  	delete fOptimizer;
}


// InitCheck
status_t
ComplexLayouter::InitCheck() const
{
	if (!fConstraints || !fWeights || !fSums || !fSumBackups || !fOptimizer)
		return B_NO_MEMORY;
	return fOptimizer->InitCheck();
}


// AddConstraints
void
ComplexLayouter::AddConstraints(int32 element, int32 length,
	float _min, float _max, float _preferred)
{
	if (element < 0 || length <= 0 || element + length > fElementCount)
		return;

	TRACE("%p->ComplexLayouter::AddConstraints(%ld, %ld, %ld, %ld, %ld)\n",
		this, element, length, (int32)_min, (int32)_max, (int32)_preferred);

	int32 spacing = fSpacing * (length - 1);
	int32 min = (int32)_min + 1 - spacing;
	int32 max = (int32)_max + 1 - spacing;

	if (min < 0)
		min = 0;
	if (max > fUnlimited)
		max = fUnlimited;

	int32 end = element + length - 1;
	Constraint** slot = fConstraints + end;
	while (*slot != NULL && (*slot)->start > element)
		slot = &(*slot)->next;

	if (*slot != NULL && (*slot)->start == element) {
		// previous constraint exists -- use stricter values
		(*slot)->Restrict(min, max);
	} else {
		// no previous constraint -- create new one
		Constraint* constraint = new(nothrow) Constraint(element, end, min,
			max);
		if (!constraint)
			return;
		constraint->next = *slot;
		*slot = constraint;
	}

	fMinMaxValid = false;
}


// SetWeight
void
ComplexLayouter::SetWeight(int32 element, float weight)
{
	if (element < 0 || element >= fElementCount)
		return;

	fWeights[element] = max_c(weight, 0);
}


// MinSize
float
ComplexLayouter::MinSize()
{
	_ValidateLayout();
	return fMin;
}


// MaxSize
float
ComplexLayouter::MaxSize()
{
	_ValidateLayout();
	return fMax;
}


// PreferredSize
float
ComplexLayouter::PreferredSize()
{
	return fMin;
}


// CreateLayoutInfo
LayoutInfo*
ComplexLayouter::CreateLayoutInfo()
{
	MyLayoutInfo* layoutInfo = new(nothrow) MyLayoutInfo(fElementCount,
		fSpacing);
	if (layoutInfo && !layoutInfo->fLocations) {
		delete layoutInfo;
		return NULL;
	}

	return layoutInfo;
}


// Layout
void
ComplexLayouter::Layout(LayoutInfo* _layoutInfo, float _size)
{
	TRACE("%p->ComplexLayouter::Layout(%ld)\n", this, (int32)_size);

	if (fElementCount == 0)
		return;

	_ValidateLayout();

	MyLayoutInfo* layoutInfo = (MyLayoutInfo*)_layoutInfo;

	int32 min = fSums[fElementCount].min;
	int32 max = fSums[fElementCount].max;

	int32 size = (int32)_size + 1 - (fElementCount - 1) * fSpacing;
	if (size < min)
		size = min;
	if (size > max)
		size = max;

	SumItem sums[fElementCount + 1];
	memcpy(sums, fSums, (fElementCount + 1) * sizeof(SumItem));

	sums[fElementCount].min = size;
	sums[fElementCount].max = size;
	sums[fElementCount].minDirty = (size != min);
	sums[fElementCount].maxDirty = (size != max);

	// propagate the size
	_PropagateChangesBack(sums, fElementCount - 1, NULL);
	_PropagateChanges(sums, fElementCount - 1, NULL);

#if TRACE_COMPLEX_LAYOUTER
	TRACE("Layout(%ld)\n", size);
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = sums[i + 1];
		TRACE("[%ld] minc = %4ld,  maxc = %4ld\n", i + 1, sum.min, sum.max);
	}
#endif

	int32 sizes[fElementCount];
	if (!_Layout(size, sums, sizes)) {
	}

	layoutInfo->InitFromSizes(sizes);
}


// CloneLayouter
Layouter*
ComplexLayouter::CloneLayouter()
{
	ComplexLayouter* layouter
		= new(nothrow) ComplexLayouter(fElementCount, fSpacing);
	ObjectDeleter<ComplexLayouter> layouterDeleter(layouter);
	if (!layouter || layouter->InitCheck() != B_OK
		|| !layouter->fOptimizer->AddConstraintsFrom(fOptimizer)) {
		return NULL;
	}

	// clone the constraints
	for (int32 i = 0; i < fElementCount; i++) {
		Constraint* constraint = fConstraints[i];
		Constraint** end = layouter->fConstraints + i;
		while (constraint) {
			*end = new(nothrow) Constraint(constraint->start, constraint->end,
				constraint->min, constraint->max);
			if (!*end)
				return NULL;

			end = &(*end)->next;
			constraint = constraint->next;
		}
	}

	// copy the other stuff
	memcpy(layouter->fWeights, fWeights, fElementCount * sizeof(float));
	memcpy(layouter->fSums, fSums, (fElementCount + 1) * sizeof(SumItem));
	memcpy(layouter->fSumBackups, fSumBackups,
		(fElementCount + 1) * sizeof(SumItemBackup));
	layouter->fMin = fMin;
	layouter->fMax = fMax;
	layouter->fMinMaxValid = fMinMaxValid;

	return layouterDeleter.Detach();
}


// _Layout
bool
ComplexLayouter::_Layout(int32 size, SumItem* sums, int32* sizes)
{
	// prepare the desired solution
	SimpleLayouter::DistributeSize(size, fWeights, sizes, fElementCount);
	if (_SatisfiesConstraints(sizes)) {
		// The desired solution already satisfies all constraints.
		return true;
	}

	double realSizes[fElementCount];
	for (int32 i = 0; i < fElementCount; i++)
		realSizes[i] = sizes[i];

	if (!_AddOptimizerConstraints())
		return false;


	// prepare a feasible solution (the minimum)
	double values[fElementCount];
	for (int32 i = 0; i < fElementCount; i++)
		values[i] = sums[i + 1].min - sums[i].min;

#if TRACE_COMPLEX_LAYOUTER
	TRACE("feasible solution vs. desired solution:\n");
	for (int32 i = 0; i < fElementCount; i++)
		TRACE("%8.4f   %8.4f\n", values[i], realSizes[i]);
#endif

	// solve
	TRACE_ONLY(bigtime_t time = system_time();)
	if (!fOptimizer->Solve(realSizes, size, values))
		return false;
	TRACE_ONLY(time = system_time() - time;)

	// compute integer solution
	// The basic strategy is to floor() the sums. This guarantees that the
	// difference between two rounded sums remains in the range of floor()
	// and ceil() of their real value difference. Since the constraints have
	// integer values, the integer solution will therefore satisfy all
	// constraints the real solution satisfied.
	TRACE("computed solution in %lld us:\n", time);

	double realSum = 0;
	double previousSum = 0;
	for (int32 i = 0; i < fElementCount; i++) {
		realSum += values[i];
		double roundedRealSum = floor(realSum);
		if (fuzzy_equals(realSum, roundedRealSum + 1))
			realSum = roundedRealSum + 1;
		sizes[i] = int32(roundedRealSum - previousSum);
		previousSum = roundedRealSum;

		TRACE("x[%ld] = %8.4f   %4ld\n", i, values[i], sizes[i]);
	}

	return _SatisfiesConstraints(sizes);
}


// _AddOptimizerConstraints
bool
ComplexLayouter::_AddOptimizerConstraints()
{
	if (fOptimizerConstraintsAdded)
		return true;

	fOptimizer->RemoveAllConstraints();

	// add constraints
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = fSums[i + 1];

		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			SumItem& base = fSums[constraint->start];
			int32 sumMin = base.min + constraint->min;
			int32 baseMax = sum.max - constraint->min;
			bool minRedundant = (sumMin < sum.min && baseMax > base.max);

			int32 sumMax = base.max + constraint->effectiveMax;
			int32 baseMin = sum.min - constraint->effectiveMax;
			bool maxRedundant = (sumMax > sum.max && baseMin < base.min);

			if (!minRedundant || !maxRedundant) {
				bool success = true;
				if (constraint->min == constraint->effectiveMax) {
					// min and max equal -- add an equality constraint
					success = fOptimizer->AddConstraint(constraint->start - 1,
						constraint->end, constraint->min, true);
				} else {
					// min and max not equal -- add them individually,
					// unless redundant
					if (!minRedundant) {
						success |= fOptimizer->AddConstraint(
							constraint->start - 1, constraint->end,
							constraint->min, false);
					}
					if (!maxRedundant) {
						success |= fOptimizer->AddConstraint(constraint->end,
							constraint->start - 1,
							-constraint->effectiveMax, false);
					}
				}

				if (!success)
					return false;
			}

			constraint = constraint->next;
		}
	}

	fOptimizerConstraintsAdded = true;
	return true;
}


// _SatisfiesConstraints
bool
ComplexLayouter::_SatisfiesConstraints(int32* sizes) const
{
	int32 sumValues[fElementCount + 1];
	sumValues[0] = 0;
	for (int32 i = 0; i < fElementCount; i++)
		sumValues[i + 1] = sumValues[i] + sizes[i];

	return _SatisfiesConstraintsSums(sumValues);
}


// _SatisfiesConstraintsSums
bool
ComplexLayouter::_SatisfiesConstraintsSums(int32* sumValues) const
{
	for (int32 i = 0; i < fElementCount; i++) {
		Constraint* constraint = fConstraints[i];
		while (constraint) {
			if (!constraint->IsSatisfied(sumValues))
				return false;

			constraint = constraint->next;
		}
	}

	return true;
}


// _ValidateLayout
void
ComplexLayouter::_ValidateLayout()
{
	// The general idea for computing the min and max for the given constraints
	// is that we rewrite the problem a little. Instead of considering the
	// x_1, ... x_n (n = fElementCount) and the constraints of the form
	//   x_i + ... + x_{i+j} >= min[i,j] and
	//   x_i + ... + x_{i+j} >= max[i,j], with i >= 1, j >= 0, i + j <= n
	//   and min[i,j], max[i,j] >= 0
	// we define
	//   c[0] = 0
	//   c[i] = \sum_{k=1}^i x_k, for all i, 1 <= i <= n
	// and thus the constraints read:
	//   c[i+j] - c[i-1] >= min[i,j]
	//   c[i+j] - c[i-1] <= max[i,j]
	//
	// Let minc[i] and maxc[i] the limits imposed by the given constraints, i.e.
	//   minc[i] <= c[i] <= maxc[i] for any tuple of (c[i])_i satisfying the
	// constraints (minc[i] and maxc[i] are unique), then we gain:
	//   minc[i+j] >= c[i-1] + min[i,j]
	//   maxc[i+j] <= c[i-1] + min[i,j]
	//   minc[i-1] >= minc[i+j] - max[i,j]
	//   maxc[i-1] >= maxc[i+j] - min[i,j]
	// We can compute the minc[i] and maxc[i] in an iterative process,
	// propagating the first to kinds of constraints forward and the other two
	// backwards. First we start considering all min constraints only. They
	// can't contradict each other and are usually to be enforced over max
	// constraints. Afterwards we add the max constraints one by one. For each
	// one of them we propagate resulting changes back and forth. In case of
	// a conflict, we relax the max constraint as much as necessary to yield
	// a consistent set of constraints. After all constraints have been
	// incorporated, the resulting minc[n] and maxc[n] are the min and max
	// limits we wanted to compute.

	if (fMinMaxValid)
		return;

	fSums[0].min = 0;
	fSums[0].max = 0;

	int32 maxSum = 0;
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = fSums[i + 1];
		sum.min = 0;
		sum.max = maxSum += fUnlimited;
		sum.minDirty = false;
		sum.maxDirty = false;
	}

	// apply min constraints forward:
	//   minc[i+j] >= minc[i-1] + min[i,j]
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = fSums[i + 1];

		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			int32 minSum = fSums[constraint->start].min + constraint->min;
			//Do not allow the cumulative minimum at fSums[i+1].min to be less than the
			//cumulative minimum already established at fSums[i].min (fSums[i] may have been
			//ignored if fSums[constraint->start] evaluates to, say, fSums[i-1]).
			if (minSum < fSums[i].min) {
				minSum = fSums[i].min;
			}
			if (minSum > sum.min) {
				sum.min = minSum;
			} else {
				TRACE("min constraint is redundant: x%ld + ... + x%ld >= %ld\n",
					constraint->start, constraint->end, constraint->min);
			}

			constraint = constraint->next;
		}
	}

	// apply min constraints backwards:
	//   maxc[i-1] <= maxc[i+j] - min[i,j]
	for (int32 i = fElementCount - 1; i >= 0; i--) {
		SumItem& sum = fSums[i + 1];

		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			SumItem& base = fSums[constraint->start];
			int32 baseMax = sum.max - constraint->min;
			if (baseMax < base.max)
				base.max = baseMax;

			constraint = constraint->next;
		}
	}

	// apply max constraints
	for (int32 i = 0; i < fElementCount; i++) {
		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			_ApplyMaxConstraint(constraint, i);

			constraint = constraint->next;
		}
	}

#if TRACE_COMPLEX_LAYOUTER
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = fSums[i + 1];
		TRACE("[%ld] minc = %4ld,  maxc = %4ld\n", i + 1, sum.min, sum.max);
	}
#endif

	if (fElementCount == 0) {
		fMin = -1;
		fMax = B_SIZE_UNLIMITED;
	} else {
		int32 spacing = (fElementCount - 1) * fSpacing;
		fMin = fSums[fElementCount].min + spacing - 1;
		fMax = fSums[fElementCount].max + spacing - 1;
		if (fMax >= fUnlimited)
			fMax = B_SIZE_UNLIMITED;
	}

	fOptimizerConstraintsAdded = false;
	fMinMaxValid = true;
}


// _ApplyMaxConstraint
void
ComplexLayouter::_ApplyMaxConstraint(Constraint* currentConstraint, int32 index)
{
	SumItem& sum = fSums[index + 1];
	SumItem& base = fSums[currentConstraint->start];

	// We want to apply:
	//   c[i+j] <= c[i-1] + max[i,j]
	//
	// This has the following direct consequences (let k = i + j):
	// (1) maxc[k] <= maxc[i-1] + max[i,j]
	// (2) minc[i-1] >= minc[k] - max[i,j]
	//
	// If maxc[k] or minc[i-i] changed, those changes have to be propagated
	// back.

	// apply (1) maxc[k] <= maxc[i-1] + max[i,j]
	int32 max = currentConstraint->effectiveMax;
	int32 sumMax = base.max + max;

	// enforce maxc[i+j] >= minc[i+j]
	if (sumMax < sum.min) {
		sumMax = sum.min;
		max = sumMax - base.max;
	}

	// apply (2) minc[i-1] >= minc[k] - max[i,j]
	// and check minc[i-1] <= maxc[i-1]
	int32 baseMin = sum.min - max;
	if (baseMin > base.max) {
		baseMin = base.max;
		max = sum.min - baseMin;
		sumMax = base.max + max;
	}

	if (currentConstraint->effectiveMax != max) {
		TRACE("relaxing conflicting max constraint (1): "
			"x%ld + ... + x%ld <= %ld -> %ld\n", currentConstraint->start,
			currentConstraint->end, currentConstraint->effectiveMax, max);
	}
	currentConstraint->effectiveMax = max;

	if (baseMin <= base.min && sumMax >= sum.max) {
		TRACE("max constraint is redundant: x%ld + ... + x%ld <= %ld\n",
			currentConstraint->start, currentConstraint->end,
			currentConstraint->effectiveMax);
		return;
	}

	// backup old values, in case we detect a conflict later
	_BackupValues(index);

	int32 diff;
	do {
		// apply the changes
		int32 changedIndex = currentConstraint->start;

		if (baseMin > base.min) {
			base.min = baseMin;
			base.minDirty = true;
		}

		if (sumMax < sum.max) {
			changedIndex = index;
			sum.max = sumMax;
			sum.maxDirty = true;
		}

		// propagate the changes
		_PropagateChangesBack(fSums, changedIndex, currentConstraint);
		_PropagateChanges(fSums, index, currentConstraint);

		// check the new constraint again -- if it doesn't hold, it
		// conflicts with the other constraints
		diff = 0;

		// check (1) maxc[k] <= maxc[i-1] + max[i,j]
		max = currentConstraint->effectiveMax;
		sumMax = base.max + max;
		if (sumMax < sum.max)
			diff = sum.max - sumMax;

		// check (2) minc[i-1] >= minc[k] - max[i,j]
		baseMin = sum.min - max;
		if (baseMin > base.min)
			diff = max_c(diff, baseMin - base.min);

		// clear the dirty flags
		for (int32 i = 0; i <= changedIndex; i++) {
			SumItem& sum = fSums[i + 1];
			sum.minDirty = false;
			sum.maxDirty = false;
		}

		// if we've got a conflict, we relax the constraint and try again
		if (diff > 0) {
			max += diff;
			TRACE("relaxing conflicting max constraint (2): "
				"x%ld + ... + x%ld <= %ld -> %ld\n", currentConstraint->start,
				currentConstraint->end, currentConstraint->effectiveMax, max);
			currentConstraint->effectiveMax = max;

			_RestoreValues(index);

			sumMax = base.max + max;
			baseMin = sum.min - max;

			if (baseMin <= base.min && sumMax >= sum.max)
				return;
		}
	} while (diff > 0);
}


// _PropagateChanges
/*!	Propagate changes forward using min and max constraints. Max constraints
	Beyond \a toIndex or at \a to toIndex after (and including)
	\a lastMaxConstraint will be ignored. To have all constraints be
	considered pass \c fElementCount and \c NULL.
*/
void
ComplexLayouter::_PropagateChanges(SumItem* sums, int32 toIndex,
	Constraint* lastMaxConstraint)
{
	for (int32 i = 0; i < fElementCount; i++) {
		SumItem& sum = sums[i + 1];

		bool ignoreMaxConstraints = (i > toIndex);

		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			SumItem& base = sums[constraint->start];

			if (constraint == lastMaxConstraint)
				ignoreMaxConstraints = true;

			// minc[k] >= minc[i-1] + min[i,j]
			if (base.minDirty) {
				int32 sumMin = base.min + constraint->min;
				if (sumMin > sum.min) {
					sum.min = sumMin;
					sum.minDirty = true;
				}
			}

			// maxc[k] <= maxc[i-1] + max[i,j]
			if (base.maxDirty && !ignoreMaxConstraints) {
				int32 sumMax = base.max + constraint->effectiveMax;
				if (sumMax < sum.max) {
					sum.max = sumMax;
					sum.maxDirty = true;
				}
			}

			constraint = constraint->next;
		}

		if (sum.minDirty || sum.maxDirty) {
			if (sum.min > sum.max) {
				// TODO: Can this actually happen?
				TRACE("adjusted max in propagation phase: index: "
					"%ld: %ld -> %ld\n", i, sum.max, sum.min);
				sum.max = sum.min;
				sum.maxDirty = true;
			}
		}
	}
}


// _PropagateChangesBack
void
ComplexLayouter::_PropagateChangesBack(SumItem* sums, int32 changedIndex,
	Constraint* lastMaxConstraint)
{
	for (int32 i = changedIndex; i >= 0; i--) {
		SumItem& sum = sums[i + 1];

		bool ignoreMaxConstraints = false;

		Constraint* constraint = fConstraints[i];
		while (constraint != NULL) {
			SumItem& base = sums[constraint->start];

			if (constraint == lastMaxConstraint)
				ignoreMaxConstraints = true;

			// minc[i-1] >= minc[k] - max[i,j]
			if (sum.minDirty && !ignoreMaxConstraints) {
				int32 baseMin = sum.min - constraint->effectiveMax;
				if (baseMin > base.min) {
					if (baseMin > base.max) {
						TRACE("min above max in back propagation phase: index: "
							"(%ld -> %ld), min: %ld, max: %ld\n", i,
							constraint->start, baseMin, base.max);
					}
					base.min = baseMin;
					base.minDirty = true;
				}
			}

			// maxc[i-1] <= maxc[k] - min[i,j]
			if (sum.maxDirty) {
				int32 baseMax = sum.max - constraint->min;
				if (baseMax < base.max) {
					if (baseMax < base.min) {
						TRACE("max below min in back propagation phase: index: "
							"(%ld -> %ld), max: %ld, min: %ld\n", i,
							constraint->start, baseMax, base.min);
					}
					base.max = baseMax;
					base.maxDirty = true;
				}
			}

			constraint = constraint->next;
		}
	}
}


// _BackupValues
void
ComplexLayouter::_BackupValues(int32 maxIndex)
{
	for (int32 i = 0; i <= maxIndex; i++) {
		SumItem& sum = fSums[i + 1];
		fSumBackups[i + 1].min = sum.min;
		fSumBackups[i + 1].max = sum.max;
	}
}


// _RestoreValues
void
ComplexLayouter::_RestoreValues(int32 maxIndex)
{
	for (int32 i = 0; i <= maxIndex; i++) {
		SumItem& sum = fSums[i + 1];
		sum.min = fSumBackups[i + 1].min;
		sum.max = fSumBackups[i + 1].max;
	}
}