forked from mirrors/gecko-dev
265e672179
# ignore-this-changeset --HG-- extra : amend_source : 4d301d3b0b8711c4692392aa76088ba7fd7d1022
127 lines
4.3 KiB
C++
127 lines
4.3 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_JustificationUtils_h_
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#define mozilla_JustificationUtils_h_
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#include "mozilla/Attributes.h"
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#include "nsCoord.h"
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namespace mozilla {
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/**
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* Jutification Algorithm
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*
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* The justification algorithm is based on expansion opportunities
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* between justifiable clusters. By this algorithm, there is one
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* expansion opportunity at each side of a justifiable cluster, and
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* at most one opportunity between two clusters. For example, if there
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* is a line in a Chinese document is: "你好世界hello world", then
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* the expansion opportunities (marked as '*') would be:
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*
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* 你*好*世*界*hello*' '*world
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*
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* The spacing left in a line will then be distributed equally to each
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* opportunities. Because we want that, only justifiable clusters get
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* expanded, and the split point between two justifiable clusters would
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* be at the middle of the spacing, each expansion opportunities will be
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* filled by two justification gaps. The example above would be:
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*
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* 你 | 好 | 世 | 界 |hello| ' ' |world
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*
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* In the algorithm, information about expansion opportunities is stored
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* in structure JustificationInfo, and the assignment of justification
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* gaps is in structure JustificationAssignment.
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*/
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struct JustificationInfo {
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// Number of expansion opportunities inside a span. It doesn't include
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// any opportunities between this span and the one before or after.
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int32_t mInnerOpportunities;
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// The justifiability of the start and end sides of the span.
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bool mIsStartJustifiable;
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bool mIsEndJustifiable;
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constexpr JustificationInfo()
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: mInnerOpportunities(0),
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mIsStartJustifiable(false),
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mIsEndJustifiable(false) {}
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// Claim that the last opportunity should be cancelled
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// because the trailing space just gets trimmed.
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void CancelOpportunityForTrimmedSpace() {
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if (mInnerOpportunities > 0) {
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mInnerOpportunities--;
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} else {
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// There is no inner opportunities, hence the whole frame must
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// contain only the trimmed space, because any content before
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// space would cause an inner opportunity. The space made each
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// side justifiable, which should be cancelled now.
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mIsStartJustifiable = false;
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mIsEndJustifiable = false;
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}
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}
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};
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struct JustificationAssignment {
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// There are at most 2 gaps per end, so it is enough to use 2 bits.
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uint8_t mGapsAtStart : 2;
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uint8_t mGapsAtEnd : 2;
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constexpr JustificationAssignment() : mGapsAtStart(0), mGapsAtEnd(0) {}
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int32_t TotalGaps() const { return mGapsAtStart + mGapsAtEnd; }
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};
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struct JustificationApplicationState {
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struct {
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// The total number of justification gaps to be processed.
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int32_t mCount;
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// The number of justification gaps which have been handled.
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int32_t mHandled;
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} mGaps;
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struct {
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// The total spacing left in a line before justification.
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nscoord mAvailable;
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// The spacing has been consumed by handled justification gaps.
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nscoord mConsumed;
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} mWidth;
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JustificationApplicationState(int32_t aGaps, nscoord aWidth) {
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mGaps.mCount = aGaps;
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mGaps.mHandled = 0;
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mWidth.mAvailable = aWidth;
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mWidth.mConsumed = 0;
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}
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bool IsJustifiable() const {
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return mGaps.mCount > 0 && mWidth.mAvailable > 0;
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}
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nscoord Consume(int32_t aGaps) {
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mGaps.mHandled += aGaps;
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nscoord newAllocate = (mWidth.mAvailable * mGaps.mHandled) / mGaps.mCount;
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nscoord deltaWidth = newAllocate - mWidth.mConsumed;
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mWidth.mConsumed = newAllocate;
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return deltaWidth;
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}
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};
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class JustificationUtils {
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public:
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// Compute justification gaps should be applied on a unit.
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static int32_t CountGaps(const JustificationInfo& aInfo,
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const JustificationAssignment& aAssign) {
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// Justification gaps include two gaps for each inner opportunities
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// and the gaps given assigned to the ends.
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return aInfo.mInnerOpportunities * 2 + aAssign.TotalGaps();
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}
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};
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} // namespace mozilla
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#endif /* !defined(mozilla_JustificationUtils_h_) */
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