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       1             : /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
       3             : /* This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : #ifndef mozilla_JustificationUtils_h_
       8             : #define mozilla_JustificationUtils_h_
       9             : 
      10             : #include "mozilla/Attributes.h"
      11             : #include "nsCoord.h"
      12             : 
      13             : namespace mozilla {
      14             : 
      15             : /**
      16             :  * Jutification Algorithm
      17             :  *
      18             :  * The justification algorithm is based on expansion opportunities
      19             :  * between justifiable clusters.  By this algorithm, there is one
      20             :  * expansion opportunity at each side of a justifiable cluster, and
      21             :  * at most one opportunity between two clusters. For example, if there
      22             :  * is a line in a Chinese document is: "你好世界hello world", then
      23             :  * the expansion opportunities (marked as '*') would be:
      24             :  *
      25             :  *                    你*好*世*界*hello*' '*world
      26             :  *
      27             :  * The spacing left in a line will then be distributed equally to each
      28             :  * opportunities. Because we want that, only justifiable clusters get
      29             :  * expanded, and the split point between two justifiable clusters would
      30             :  * be at the middle of the spacing, each expansion opportunities will be
      31             :  * filled by two justification gaps. The example above would be:
      32             :  *
      33             :  *              你 | 好 | 世 | 界  |hello|  ' '  |world
      34             :  *
      35             :  * In the algorithm, information about expansion opportunities is stored
      36             :  * in structure JustificationInfo, and the assignment of justification
      37             :  * gaps is in structure JustificationAssignment.
      38             :  */
      39             : 
      40             : struct JustificationInfo
      41             : {
      42             :   // Number of expansion opportunities inside a span. It doesn't include
      43             :   // any opportunities between this span and the one before or after.
      44             :   int32_t mInnerOpportunities;
      45             :   // The justifiability of the start and end sides of the span.
      46             :   bool mIsStartJustifiable;
      47             :   bool mIsEndJustifiable;
      48             : 
      49         375 :   constexpr JustificationInfo()
      50         375 :     : mInnerOpportunities(0)
      51             :     , mIsStartJustifiable(false)
      52         375 :     , mIsEndJustifiable(false)
      53             :   {
      54         375 :   }
      55             : 
      56             :   // Claim that the last opportunity should be cancelled
      57             :   // because the trailing space just gets trimmed.
      58           0 :   void CancelOpportunityForTrimmedSpace()
      59             :   {
      60           0 :     if (mInnerOpportunities > 0) {
      61           0 :       mInnerOpportunities--;
      62             :     } else {
      63             :       // There is no inner opportunities, hence the whole frame must
      64             :       // contain only the trimmed space, because any content before
      65             :       // space would cause an inner opportunity. The space made each
      66             :       // side justifiable, which should be cancelled now.
      67           0 :       mIsStartJustifiable = false;
      68           0 :       mIsEndJustifiable = false;
      69             :     }
      70           0 :   }
      71             : };
      72             : 
      73             : struct JustificationAssignment
      74             : {
      75             :   // There are at most 2 gaps per end, so it is enough to use 2 bits.
      76             :   uint8_t mGapsAtStart : 2;
      77             :   uint8_t mGapsAtEnd : 2;
      78             : 
      79         150 :   constexpr JustificationAssignment()
      80         150 :     : mGapsAtStart(0)
      81         150 :     , mGapsAtEnd(0)
      82             :   {
      83         150 :   }
      84             : 
      85           0 :   int32_t TotalGaps() const { return mGapsAtStart + mGapsAtEnd; }
      86             : };
      87             : 
      88             : struct JustificationApplicationState
      89             : {
      90             :   struct
      91             :   {
      92             :     // The total number of justification gaps to be processed.
      93             :     int32_t mCount;
      94             :     // The number of justification gaps which have been handled.
      95             :     int32_t mHandled;
      96             :   } mGaps;
      97             : 
      98             :   struct
      99             :   {
     100             :     // The total spacing left in a line before justification.
     101             :     nscoord mAvailable;
     102             :     // The spacing has been consumed by handled justification gaps.
     103             :     nscoord mConsumed;
     104             :   } mWidth;
     105             : 
     106           0 :   JustificationApplicationState(int32_t aGaps, nscoord aWidth)
     107           0 :   {
     108           0 :     mGaps.mCount = aGaps;
     109           0 :     mGaps.mHandled = 0;
     110           0 :     mWidth.mAvailable = aWidth;
     111           0 :     mWidth.mConsumed = 0;
     112           0 :   }
     113             : 
     114           0 :   bool IsJustifiable() const
     115             :   {
     116           0 :     return mGaps.mCount > 0 && mWidth.mAvailable > 0;
     117             :   }
     118             : 
     119           0 :   nscoord Consume(int32_t aGaps)
     120             :   {
     121           0 :     mGaps.mHandled += aGaps;
     122           0 :     nscoord newAllocate = (mWidth.mAvailable * mGaps.mHandled) / mGaps.mCount;
     123           0 :     nscoord deltaWidth = newAllocate - mWidth.mConsumed;
     124           0 :     mWidth.mConsumed = newAllocate;
     125           0 :     return deltaWidth;
     126             :   }
     127             : };
     128             : 
     129             : class JustificationUtils
     130             : {
     131             : public:
     132             :   // Compute justification gaps should be applied on a unit.
     133           0 :   static int32_t CountGaps(const JustificationInfo& aInfo,
     134             :                            const JustificationAssignment& aAssign)
     135             :   {
     136             :     // Justification gaps include two gaps for each inner opportunities
     137             :     // and the gaps given assigned to the ends.
     138           0 :     return aInfo.mInnerOpportunities * 2 + aAssign.TotalGaps();
     139             :   }
     140             : };
     141             : 
     142             : } // namespace mozilla
     143             : 
     144             : #endif /* !defined(mozilla_JustificationUtils_h_) */