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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_JustificationUtils_h_
#define mozilla_JustificationUtils_h_
#include "mozilla/Attributes.h"
#include "nsCoord.h"
namespace mozilla {
/**
* Jutification Algorithm
*
* The justification algorithm is based on expansion opportunities
* between justifiable clusters. By this algorithm, there is one
* expansion opportunity at each side of a justifiable cluster, and
* at most one opportunity between two clusters. For example, if there
* is a line in a Chinese document is: "你好世界hello world", then
* the expansion opportunities (marked as '*') would be:
*
* 你*好*世*界*hello*' '*world
*
* The spacing left in a line will then be distributed equally to each
* opportunities. Because we want that, only justifiable clusters get
* expanded, and the split point between two justifiable clusters would
* be at the middle of the spacing, each expansion opportunities will be
* filled by two justification gaps. The example above would be:
*
* 你 | 好 | 世 | 界 |hello| ' ' |world
*
* In the algorithm, information about expansion opportunities is stored
* in structure JustificationInfo, and the assignment of justification
* gaps is in structure JustificationAssignment.
*/
struct JustificationInfo
{
// Number of expansion opportunities inside a span. It doesn't include
// any opportunities between this span and the one before or after.
int32_t mInnerOpportunities;
// The justifiability of the start and end sides of the span.
bool mIsStartJustifiable;
bool mIsEndJustifiable;
constexpr JustificationInfo()
: mInnerOpportunities(0)
, mIsStartJustifiable(false)
, mIsEndJustifiable(false)
{
}
// Claim that the last opportunity should be cancelled
// because the trailing space just gets trimmed.
void CancelOpportunityForTrimmedSpace()
{
if (mInnerOpportunities > 0) {
mInnerOpportunities--;
} else {
// There is no inner opportunities, hence the whole frame must
// contain only the trimmed space, because any content before
// space would cause an inner opportunity. The space made each
// side justifiable, which should be cancelled now.
mIsStartJustifiable = false;
mIsEndJustifiable = false;
}
}
};
struct JustificationAssignment
{
// There are at most 2 gaps per end, so it is enough to use 2 bits.
uint8_t mGapsAtStart : 2;
uint8_t mGapsAtEnd : 2;
constexpr JustificationAssignment()
: mGapsAtStart(0)
, mGapsAtEnd(0)
{
}
int32_t TotalGaps() const { return mGapsAtStart + mGapsAtEnd; }
};
struct JustificationApplicationState
{
struct
{
// The total number of justification gaps to be processed.
int32_t mCount;
// The number of justification gaps which have been handled.
int32_t mHandled;
} mGaps;
struct
{
// The total spacing left in a line before justification.
nscoord mAvailable;
// The spacing has been consumed by handled justification gaps.
nscoord mConsumed;
} mWidth;
JustificationApplicationState(int32_t aGaps, nscoord aWidth)
{
mGaps.mCount = aGaps;
mGaps.mHandled = 0;
mWidth.mAvailable = aWidth;
mWidth.mConsumed = 0;
}
bool IsJustifiable() const
{
return mGaps.mCount > 0 && mWidth.mAvailable > 0;
}
nscoord Consume(int32_t aGaps)
{
mGaps.mHandled += aGaps;
nscoord newAllocate = (mWidth.mAvailable * mGaps.mHandled) / mGaps.mCount;
nscoord deltaWidth = newAllocate - mWidth.mConsumed;
mWidth.mConsumed = newAllocate;
return deltaWidth;
}
};
class JustificationUtils
{
public:
// Compute justification gaps should be applied on a unit.
static int32_t CountGaps(const JustificationInfo& aInfo,
const JustificationAssignment& aAssign)
{
// Justification gaps include two gaps for each inner opportunities
// and the gaps given assigned to the ends.
return aInfo.mInnerOpportunities * 2 + aAssign.TotalGaps();
}
};
} // namespace mozilla
#endif /* !defined(mozilla_JustificationUtils_h_) */
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