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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_) */