src/third_party/WebKit/Source/platform/text/StringTruncator.cpp

   1 /*
   2  * Copyright (C) 2005, 2006, 2007 Apple Inc.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  * 1.  Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  * 2.  Redistributions in binary form must reproduce the above copyright
  11  *     notice, this list of conditions and the following disclaimer in the
  12  *     documentation and/or other materials provided with the distribution.
  13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
  14  *     its contributors may be used to endorse or promote products derived
  15  *     from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #include "config.h"
  30 #include "platform/text/StringTruncator.h"
  31
  32 #include "platform/fonts/Font.h"
  33 #include "platform/text/TextBreakIterator.h"
  34 #include "platform/text/TextRun.h"
  35 #include "wtf/Assertions.h"
  36 #include "wtf/unicode/CharacterNames.h"
  37
  38 namespace blink {
  39
  40 #define STRING_BUFFER_SIZE 2048
  41
  42 typedef unsigned TruncationFunction(const String&, unsigned length, unsigned keepCount, UChar* buffer);
  43
  44 static inline int textBreakAtOrPreceding(const NonSharedCharacterBreakIterator& it, int offset)
  45 {
  46     if (it.isBreak(offset))
  47         return offset;
  48
  49     int result = it.preceding(offset);
  50     return result == TextBreakDone ? 0 : result;
  51 }
  52
  53 static inline int boundedTextBreakFollowing(const NonSharedCharacterBreakIterator& it, int offset, int length)
  54 {
  55     int result = it.following(offset);
  56     return result == TextBreakDone ? length : result;
  57 }
  58
  59 static unsigned centerTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer)
  60 {
  61     ASSERT(keepCount < length);
  62     ASSERT(keepCount < STRING_BUFFER_SIZE);
  63
  64     unsigned omitStart = (keepCount + 1) / 2;
  65     NonSharedCharacterBreakIterator it(string);
  66     unsigned omitEnd = boundedTextBreakFollowing(it, omitStart + (length - keepCount) - 1, length);
  67     omitStart = textBreakAtOrPreceding(it, omitStart);
  68
  69     unsigned truncatedLength = omitStart + 1 + (length - omitEnd);
  70     ASSERT(truncatedLength <= length);
  71
  72     string.copyTo(buffer, 0, omitStart);
  73     buffer[omitStart] = horizontalEllipsis;
  74     string.copyTo(&buffer[omitStart + 1], omitEnd, length - omitEnd);
  75
  76     return truncatedLength;
  77 }
  78
  79 static unsigned rightTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer)
  80 {
  81     ASSERT(keepCount < length);
  82     ASSERT(keepCount < STRING_BUFFER_SIZE);
  83
  84     NonSharedCharacterBreakIterator it(string);
  85     unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
  86     unsigned truncatedLength = keepLength + 1;
  87
  88     string.copyTo(buffer, 0, keepLength);
  89     buffer[keepLength] = horizontalEllipsis;
  90
  91     return truncatedLength;
  92 }
  93
  94 static float stringWidth(const Font& renderer, const String& string)
  95 {
  96     TextRun run(string);
  97     return renderer.width(run);
  98 }
  99
 100 static float stringWidth(const Font& renderer, const UChar* characters, unsigned length)
 101 {
 102     TextRun run(characters, length);
 103     return renderer.width(run);
 104 }
 105
 106 static String truncateString(const String& string, float maxWidth, const Font& font, TruncationFunction truncateToBuffer)
 107 {
 108     if (string.isEmpty())
 109         return string;
 110
 111     ASSERT(maxWidth >= 0);
 112
 113     float currentEllipsisWidth = stringWidth(font, &horizontalEllipsis, 1);
 114
 115     UChar stringBuffer[STRING_BUFFER_SIZE];
 116     unsigned truncatedLength;
 117     unsigned keepCount;
 118     unsigned length = string.length();
 119
 120     if (length > STRING_BUFFER_SIZE) {
 121         keepCount = STRING_BUFFER_SIZE - 1; // need 1 character for the ellipsis
 122         truncatedLength = centerTruncateToBuffer(string, length, keepCount, stringBuffer);
 123     } else {
 124         keepCount = length;
 125         string.copyTo(stringBuffer, 0, length);
 126         truncatedLength = length;
 127     }
 128
 129     float width = stringWidth(font, stringBuffer, truncatedLength);
 130     if (width <= maxWidth)
 131         return string;
 132
 133     unsigned keepCountForLargestKnownToFit = 0;
 134     float widthForLargestKnownToFit = currentEllipsisWidth;
 135
 136     unsigned keepCountForSmallestKnownToNotFit = keepCount;
 137     float widthForSmallestKnownToNotFit = width;
 138
 139     if (currentEllipsisWidth >= maxWidth) {
 140         keepCountForLargestKnownToFit = 1;
 141         keepCountForSmallestKnownToNotFit = 2;
 142     }
 143
 144     while (keepCountForLargestKnownToFit + 1 < keepCountForSmallestKnownToNotFit) {
 145         ASSERT(widthForLargestKnownToFit <= maxWidth);
 146         ASSERT(widthForSmallestKnownToNotFit > maxWidth);
 147
 148         float ratio = (keepCountForSmallestKnownToNotFit - keepCountForLargestKnownToFit)
 149             / (widthForSmallestKnownToNotFit - widthForLargestKnownToFit);
 150         keepCount = static_cast<unsigned>(maxWidth * ratio);
 151
 152         if (keepCount <= keepCountForLargestKnownToFit) {
 153             keepCount = keepCountForLargestKnownToFit + 1;
 154         } else if (keepCount >= keepCountForSmallestKnownToNotFit) {
 155             keepCount = keepCountForSmallestKnownToNotFit - 1;
 156         }
 157
 158         ASSERT(keepCount < length);
 159         ASSERT(keepCount > 0);
 160         ASSERT(keepCount < keepCountForSmallestKnownToNotFit);
 161         ASSERT(keepCount > keepCountForLargestKnownToFit);
 162
 163         truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer);
 164
 165         width = stringWidth(font, stringBuffer, truncatedLength);
 166         if (width <= maxWidth) {
 167             keepCountForLargestKnownToFit = keepCount;
 168             widthForLargestKnownToFit = width;
 169         } else {
 170             keepCountForSmallestKnownToNotFit = keepCount;
 171             widthForSmallestKnownToNotFit = width;
 172         }
 173     }
 174
 175     if (!keepCountForLargestKnownToFit)
 176         keepCountForLargestKnownToFit = 1;
 177
 178     if (keepCount != keepCountForLargestKnownToFit) {
 179         keepCount = keepCountForLargestKnownToFit;
 180         truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer);
 181     }
 182
 183     return String(stringBuffer, truncatedLength);
 184 }
 185
 186 String StringTruncator::centerTruncate(const String& string, float maxWidth, const Font& font)
 187 {
 188     return truncateString(string, maxWidth, font, centerTruncateToBuffer);
 189 }
 190
 191 String StringTruncator::rightTruncate(const String& string, float maxWidth, const Font& font)
 192 {
 193     return truncateString(string, maxWidth, font, rightTruncateToBuffer);
 194 }
 195
 196 float StringTruncator::width(const String& string, const Font& font)
 197 {
 198     return stringWidth(font, string);
 199 }
 200
 201 } // namespace blink