StringTruncator.cpp   [plain text]

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#include "config.h"
#include "StringTruncator.h"

#include "CharacterNames.h"
#include "Font.h"
#include "TextBreakIterator.h"
#include <wtf/Assertions.h>
#include <wtf/Vector.h>

#include <wtf/UnusedParam.h>

namespace WebCore {

#define STRING_BUFFER_SIZE 2048

#define ELLIPSIS_CHARACTER 0x2026
#define SPACE_CHARACTER 0x0020

    
typedef unsigned TruncationFunction(const String&, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis);
    
static inline int textBreakAtOrPreceding(TextBreakIterator* it, int offset)
{
    if (isTextBreak(it, offset))
        return offset;

    int result = textBreakPreceding(it, offset);
    return result == TextBreakDone ? 0 : result;
}

static inline int boundedTextBreakFollowing(TextBreakIterator* it, int offset, int length)
{
    int result = textBreakFollowing(it, offset);
    return result == TextBreakDone ? length : result;
}
    
static unsigned centerTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis)
{
    ASSERT(keepCount < length);
    ASSERT(keepCount < STRING_BUFFER_SIZE);
    
    unsigned omitStart = (keepCount + 1) / 2;
    TextBreakIterator* it = characterBreakIterator(string.characters(), length);
    unsigned omitEnd = boundedTextBreakFollowing(it, omitStart + (length - keepCount) - 1, length);
    omitStart = textBreakAtOrPreceding(it, omitStart);

    // Strip single character before ellipsis character, when that character is preceded by a space
    if (omitStart > 1 && string[omitStart - 1] != SPACE_CHARACTER &&
        omitStart > 2 && string[omitStart - 2] == SPACE_CHARACTER)
        omitStart--;
    // Strip whitespace before and after the ellipsis character
    while (omitStart > 1 && string[omitStart - 1] == SPACE_CHARACTER)
        omitStart--;
    // Strip single character after ellipsis character, when that character is followed by a space
    if ((length - omitEnd) > 1 && string[omitEnd] != SPACE_CHARACTER &&
        (length - omitEnd) > 2 && string[omitEnd + 1] == SPACE_CHARACTER)
        omitEnd++;
    while ((length - omitEnd) > 1 && string[omitEnd] == SPACE_CHARACTER)
        omitEnd++;

    unsigned truncatedLength = insertEllipsis ? omitStart + 1 + (length - omitEnd) : length - (omitEnd - omitStart);
    ASSERT(truncatedLength <= length);

    memcpy(buffer, string.characters(), sizeof(UChar) * omitStart);
    if (insertEllipsis) {
        buffer[omitStart] = horizontalEllipsis;
        memcpy(&buffer[omitStart + 1], &string.characters()[omitEnd], sizeof(UChar) * (length - omitEnd));    
    } else {
        memcpy(&buffer[omitStart], &string.characters()[omitEnd], sizeof(UChar) * (length - omitEnd));
    }
    
    return truncatedLength;
}

static unsigned rightTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis)
{
    ASSERT(keepCount < length);
    ASSERT(keepCount < STRING_BUFFER_SIZE);

    // Strip single character before ellipsis character, when that character is preceded by a space
    if (keepCount > 1 && string[keepCount - 1] != SPACE_CHARACTER &&
        keepCount > 2 && string[keepCount - 2] == SPACE_CHARACTER)
        keepCount--;
    // Strip whitespace before the ellipsis character
    while (keepCount > 1 && string[keepCount - 1] == SPACE_CHARACTER)
        keepCount--;
    
    TextBreakIterator* it = characterBreakIterator(string.characters(), length);
    unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
    unsigned truncatedLength = insertEllipsis ? keepLength + 1 : keepLength;

    memcpy(buffer, string.characters(), sizeof(UChar) * keepLength);
    if (insertEllipsis)
        buffer[keepLength] = horizontalEllipsis;
    
    return truncatedLength;
}
    
static unsigned rightClipToCharacterBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis)
{
    UNUSED_PARAM(insertEllipsis);
    
    ASSERT(keepCount < length);
    ASSERT(keepCount < STRING_BUFFER_SIZE);
    
    TextBreakIterator* it = characterBreakIterator(string.characters(), length);
    unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
    memcpy(buffer, string.characters(), sizeof(UChar) * keepLength);
    
    return keepLength;
}

static unsigned rightClipToWordBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis)
{
    UNUSED_PARAM(insertEllipsis);
    
    ASSERT(keepCount < length);
    ASSERT(keepCount < STRING_BUFFER_SIZE);
    
    TextBreakIterator* it = wordBreakIterator(string.characters(), length);
    unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
    memcpy(buffer, string.characters(), sizeof(UChar) * keepLength);
    
    // Motivated by rdar://problem/7439327> truncation should not include a trailing space
    while ((keepLength > 0) && (string[keepLength - 1] == SPACE_CHARACTER))
        keepLength--;
    return keepLength;
}
    


static unsigned leftTruncateToBuffer(const String& string, unsigned length, unsigned keepCount, UChar* buffer, bool insertEllipsis)
{
    ASSERT(keepCount < length);
    ASSERT(keepCount < STRING_BUFFER_SIZE);
    
    unsigned startIndex = length - keepCount;
    
    TextBreakIterator* it = characterBreakIterator(string.characters(), length);
    unsigned adjustedStartIndex = startIndex;
    startIndex = boundedTextBreakFollowing(it, startIndex, length - startIndex);
    
    // Strip single character after ellipsis character, when that character is preceded by a space
    if (adjustedStartIndex < length && string[adjustedStartIndex] != SPACE_CHARACTER &&
        adjustedStartIndex < length - 1 && string[adjustedStartIndex + 1] == SPACE_CHARACTER)
        adjustedStartIndex++;
    // Strip whitespace after the ellipsis character
    while (adjustedStartIndex < length && string[adjustedStartIndex] == SPACE_CHARACTER)
        adjustedStartIndex++;
    
    if (insertEllipsis) {
        buffer[0] = horizontalEllipsis;
        memcpy(&buffer[1], &string.characters()[adjustedStartIndex], sizeof(UChar) * (length - adjustedStartIndex + 1));
        
        return length - adjustedStartIndex + 1;
    } else {
        memcpy(&buffer[0], &string.characters()[adjustedStartIndex], sizeof(UChar) * (length - adjustedStartIndex + 1));
        
        return length - adjustedStartIndex;
    }    
}

static float stringWidth(const Font& renderer, const UChar* characters, unsigned length, bool disableRoundingHacks)
{
    TextRun run(characters, length);
    if (disableRoundingHacks)
        run.disableRoundingHacks();
    return renderer.floatWidth(run);
}

static String truncateString(const String& string, float maxWidth, const Font& font, TruncationFunction truncateToBuffer, bool disableRoundingHacks, float *resultWidth, bool insertEllipsis = true,  float customTruncationElementWidth = 0, bool alwaysTruncate = false)
{
    if (string.isEmpty())
        return string;

    if (resultWidth)
        *resultWidth = 0;

    ASSERT(maxWidth >= 0);
    
    float currentEllipsisWidth = insertEllipsis ? stringWidth(font, &horizontalEllipsis, 1, disableRoundingHacks) : customTruncationElementWidth;
    UChar stringBuffer[STRING_BUFFER_SIZE];
    unsigned truncatedLength;
    unsigned keepCount;
    unsigned length = string.length();

    if (length > STRING_BUFFER_SIZE) {            
        if (insertEllipsis)
            keepCount = STRING_BUFFER_SIZE - 1; // need 1 character for the ellipsis
        truncatedLength = centerTruncateToBuffer(string, length, keepCount, stringBuffer, insertEllipsis);
    } else {
        keepCount = length;
        memcpy(stringBuffer, string.characters(), sizeof(UChar) * length);
        truncatedLength = length;
    }

    float width = stringWidth(font, stringBuffer, truncatedLength, disableRoundingHacks);
    if (!insertEllipsis && alwaysTruncate)
        width += customTruncationElementWidth;
    if (width <= maxWidth) {
        if (resultWidth)
            *resultWidth = width;
        return string;
    }

    unsigned keepCountForLargestKnownToFit = 0;
    float widthForLargestKnownToFit = currentEllipsisWidth;
    
    unsigned keepCountForSmallestKnownToNotFit = keepCount;
    float widthForSmallestKnownToNotFit = width;
    
    if (currentEllipsisWidth >= maxWidth) {
        keepCountForLargestKnownToFit = 1;
        keepCountForSmallestKnownToNotFit = 2;
    }
    
    while (keepCountForLargestKnownToFit + 1 < keepCountForSmallestKnownToNotFit) {
        ASSERT(widthForLargestKnownToFit <= maxWidth);
        ASSERT(widthForSmallestKnownToNotFit > maxWidth);

        float ratio = (keepCountForSmallestKnownToNotFit - keepCountForLargestKnownToFit)
            / (widthForSmallestKnownToNotFit - widthForLargestKnownToFit);
        keepCount = static_cast<unsigned>(maxWidth * ratio);
        
        if (keepCount <= keepCountForLargestKnownToFit) {
            keepCount = keepCountForLargestKnownToFit + 1;
        } else if (keepCount >= keepCountForSmallestKnownToNotFit) {
            keepCount = keepCountForSmallestKnownToNotFit - 1;
        }
        
        ASSERT(keepCount < length);
        ASSERT(keepCount > 0);
        ASSERT(keepCount < keepCountForSmallestKnownToNotFit);
        ASSERT(keepCount > keepCountForLargestKnownToFit);
        
        truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer, insertEllipsis);
        
        width = stringWidth(font, stringBuffer, truncatedLength, disableRoundingHacks);
        if (!insertEllipsis)
            width += customTruncationElementWidth;
        if (width <= maxWidth) {
            keepCountForLargestKnownToFit = keepCount;
            widthForLargestKnownToFit = width;
            if (resultWidth)
                *resultWidth = width;
        } else {
            keepCountForSmallestKnownToNotFit = keepCount;
            widthForSmallestKnownToNotFit = width;
        }
    }
    
    if (keepCountForLargestKnownToFit == 0) {
        keepCountForLargestKnownToFit = 1;
    }
    
    if (keepCount != keepCountForLargestKnownToFit) {
        keepCount = keepCountForLargestKnownToFit;
        truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer, insertEllipsis);
    }
    
    return String(stringBuffer, truncatedLength);
}

String StringTruncator::centerTruncate(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks)
{
    return truncateString(string, maxWidth, font, centerTruncateToBuffer, disableRoundingHacks, 0);
}

String StringTruncator::rightTruncate(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks)
{
    return truncateString(string, maxWidth, font, rightTruncateToBuffer, disableRoundingHacks, 0);
}

float StringTruncator::width(const String& string, const Font& font, bool disableRoundingHacks)
{
    return stringWidth(font, string.characters(), string.length(), disableRoundingHacks);
}


String StringTruncator::centerTruncate(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks, float& resultWidth, bool insertEllipsis, float customTruncationElementWidth)
{
    return truncateString(string, maxWidth, font, centerTruncateToBuffer, disableRoundingHacks, &resultWidth, insertEllipsis, customTruncationElementWidth);
}

String StringTruncator::rightTruncate(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks, float& resultWidth, bool insertEllipsis, float customTruncationElementWidth)
{
    return truncateString(string, maxWidth, font, rightTruncateToBuffer, disableRoundingHacks, &resultWidth, insertEllipsis, customTruncationElementWidth);
}

String StringTruncator::leftTruncate(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks, float& resultWidth, bool insertEllipsis, float customTruncationElementWidth)
{
    return truncateString(string, maxWidth, font, leftTruncateToBuffer, disableRoundingHacks, &resultWidth, insertEllipsis, customTruncationElementWidth);
}
    
String StringTruncator::rightClipToCharacter(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks, float& resultWidth, bool insertEllipsis, float customTruncationElementWidth) 
{
    return truncateString(string, maxWidth, font, rightClipToCharacterBuffer, disableRoundingHacks, &resultWidth, insertEllipsis, customTruncationElementWidth);
}

String StringTruncator::rightClipToWord(const String& string, float maxWidth, const Font& font, bool disableRoundingHacks, float& resultWidth, bool insertEllipsis,  float customTruncationElementWidth, bool alwaysTruncate) 
{
    return truncateString(string, maxWidth, font, rightClipToWordBuffer, disableRoundingHacks, &resultWidth, insertEllipsis, customTruncationElementWidth, alwaysTruncate);
}
    


} // namespace WebCore