Source/WebCore/platform/graphics/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
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  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 "StringTruncator.h"
  31
  32 #include "Font.h"
  33 #include "TextBreakIterator.h"
  34 #include "TextRun.h"
  35 #include <wtf/Assertions.h>
  36 #include <wtf/Vector.h>
  37 #include <wtf/unicode/CharacterNames.h>
  38
  39 namespace WebCore {
  40
  41 #define STRING_BUFFER_SIZE 2048
  42
  43 typedef unsigned TruncationFunction(const String&, unsigned length, unsigned keepCount, UChar* buffer);
  44
  45 static inline int textBreakAtOrPreceding(TextBreakIterator* it, int offset)
  46 {
  47     if (isTextBreak(it, offset))
  48         return offset;
  49
  50     int result = textBreakPreceding(it, offset);
  51     return result == TextBreakDone ? 0 : result;
  52 }
  53
  54 static inline int boundedTextBreakFollowing(TextBreakIterator* it, int offset, int length)
  55 {
  56     int result = textBreakFollowing(it, offset);
  57     return result == TextBreakDone ? length : result;
  58 }
  59
  60 static unsigned centerTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer)
  61 {
  62     ASSERT(keepCount < length);
  63     ASSERT(keepCount < STRING_BUFFER_SIZE);
  64
  65     unsigned omitStart = (keepCount + 1) / 2;
  66     TextBreakIterator* it = characterBreakIterator(string.characters(), length);
  67     unsigned omitEnd = boundedTextBreakFollowing(it, omitStart + (length - keepCount) - 1, length);
  68     omitStart = textBreakAtOrPreceding(it, omitStart);
  69
  70     unsigned truncatedLength = omitStart + 1 + (length - omitEnd);
  71     ASSERT(truncatedLength <= length);
  72
  73     memcpy(buffer, string.characters(), sizeof(UChar) * omitStart);
  74     buffer[omitStart] = horizontalEllipsis;
  75     memcpy(&buffer[omitStart + 1], &string.characters()[omitEnd], sizeof(UChar) * (length - omitEnd));
  76
  77     return truncatedLength;
  78 }
  79
  80 static unsigned rightTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer)
  81 {
  82     ASSERT(keepCount < length);
  83     ASSERT(keepCount < STRING_BUFFER_SIZE);
  84
  85     TextBreakIterator* it = characterBreakIterator(string.characters(), length);
  86     unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
  87     unsigned truncatedLength = keepLength + 1;
  88
  89     memcpy(buffer, string.characters(), sizeof(UChar) * keepLength);
  90     buffer[keepLength] = horizontalEllipsis;
  91
  92     return truncatedLength;
  93 }
  94
  95 static float stringWidth(const Font& renderer, const UChar* characters, unsigned length)
  96 {
  97     TextRun run(characters, length);
  98     return renderer.width(run);
  99 }
 100
 101 static String truncateString(const String& string, float maxWidth, const Font& font, TruncationFunction truncateToBuffer)
 102 {
 103     if (string.isEmpty())
 104         return string;
 105
 106     ASSERT(maxWidth >= 0);
 107
 108     float currentEllipsisWidth = stringWidth(font, &horizontalEllipsis, 1);
 109
 110     UChar stringBuffer[STRING_BUFFER_SIZE];
 111     unsigned truncatedLength;
 112     unsigned keepCount;
 113     unsigned length = string.length();
 114
 115     if (length > STRING_BUFFER_SIZE) {
 116         keepCount = STRING_BUFFER_SIZE - 1; // need 1 character for the ellipsis
 117         truncatedLength = centerTruncateToBuffer(string, length, keepCount, stringBuffer);
 118     } else {
 119         keepCount = length;
 120         memcpy(stringBuffer, string.characters(), sizeof(UChar) * length);
 121         truncatedLength = length;
 122     }
 123
 124     float width = stringWidth(font, stringBuffer, truncatedLength);
 125     if (width <= maxWidth)
 126         return string;
 127
 128     unsigned keepCountForLargestKnownToFit = 0;
 129     float widthForLargestKnownToFit = currentEllipsisWidth;
 130
 131     unsigned keepCountForSmallestKnownToNotFit = keepCount;
 132     float widthForSmallestKnownToNotFit = width;
 133
 134     if (currentEllipsisWidth >= maxWidth) {
 135         keepCountForLargestKnownToFit = 1;
 136         keepCountForSmallestKnownToNotFit = 2;
 137     }
 138
 139     while (keepCountForLargestKnownToFit + 1 < keepCountForSmallestKnownToNotFit) {
 140         ASSERT(widthForLargestKnownToFit <= maxWidth);
 141         ASSERT(widthForSmallestKnownToNotFit > maxWidth);
 142
 143         float ratio = (keepCountForSmallestKnownToNotFit - keepCountForLargestKnownToFit)
 144             / (widthForSmallestKnownToNotFit - widthForLargestKnownToFit);
 145         keepCount = static_cast<unsigned>(maxWidth * ratio);
 146
 147         if (keepCount <= keepCountForLargestKnownToFit) {
 148             keepCount = keepCountForLargestKnownToFit + 1;
 149         } else if (keepCount >= keepCountForSmallestKnownToNotFit) {
 150             keepCount = keepCountForSmallestKnownToNotFit - 1;
 151         }
 152
 153         ASSERT(keepCount < length);
 154         ASSERT(keepCount > 0);
 155         ASSERT(keepCount < keepCountForSmallestKnownToNotFit);
 156         ASSERT(keepCount > keepCountForLargestKnownToFit);
 157
 158         truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer);
 159
 160         width = stringWidth(font, stringBuffer, truncatedLength);
 161         if (width <= maxWidth) {
 162             keepCountForLargestKnownToFit = keepCount;
 163             widthForLargestKnownToFit = width;
 164         } else {
 165             keepCountForSmallestKnownToNotFit = keepCount;
 166             widthForSmallestKnownToNotFit = width;
 167         }
 168     }
 169
 170     if (keepCountForLargestKnownToFit == 0) {
 171         keepCountForLargestKnownToFit = 1;
 172     }
 173
 174     if (keepCount != keepCountForLargestKnownToFit) {
 175         keepCount = keepCountForLargestKnownToFit;
 176         truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer);
 177     }
 178
 179     return String(stringBuffer, truncatedLength);
 180 }
 181
 182 String StringTruncator::centerTruncate(const String& string, float maxWidth, const Font& font)
 183 {
 184     return truncateString(string, maxWidth, font, centerTruncateToBuffer);
 185 }
 186
 187 String StringTruncator::rightTruncate(const String& string, float maxWidth, const Font& font)
 188 {
 189     return truncateString(string, maxWidth, font, rightTruncateToBuffer);
 190 }
 191
 192 float StringTruncator::width(const String& string, const Font& font)
 193 {
 194     return stringWidth(font, string.characters(), string.length());
 195 }
 196
 197 } // namespace WebCore