xref: /external/webkit/Source/WebCore/platform/graphics/StringTruncator.cpp

/*
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 *
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 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#include "config.h"
#include "StringTruncator.h"

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

namespace WebCore {

#define STRING_BUFFER_SIZE 2048

typedef unsigned TruncationFunction(const String&, unsigned length, unsigned keepCount, UChar* buffer);

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)
{
    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);

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

    memcpy(buffer, string.characters(), sizeof(UChar) * omitStart);
    buffer[omitStart] = horizontalEllipsis;
    memcpy(&buffer[omitStart + 1], &string.characters()[omitEnd], sizeof(UChar) * (length - omitEnd));

    return truncatedLength;
}

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

    TextBreakIterator* it = characterBreakIterator(string.characters(), length);
    unsigned keepLength = textBreakAtOrPreceding(it, keepCount);
    unsigned truncatedLength = keepLength + 1;

    memcpy(buffer, string.characters(), sizeof(UChar) * keepLength);
    buffer[keepLength] = horizontalEllipsis;

    return truncatedLength;
}

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

static String truncateString(const String& string, float maxWidth, const Font& font, TruncationFunction truncateToBuffer)
{
    if (string.isEmpty())
        return string;

    ASSERT(maxWidth >= 0);

    float currentEllipsisWidth = stringWidth(font, &horizontalEllipsis, 1);

    UChar stringBuffer[STRING_BUFFER_SIZE];
    unsigned truncatedLength;
    unsigned keepCount;
    unsigned length = string.length();

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

    float width = stringWidth(font, stringBuffer, truncatedLength);
    if (width <= maxWidth)
        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);

        width = stringWidth(font, stringBuffer, truncatedLength);
        if (width <= maxWidth) {
            keepCountForLargestKnownToFit = keepCount;
            widthForLargestKnownToFit = width;
        } else {
            keepCountForSmallestKnownToNotFit = keepCount;
            widthForSmallestKnownToNotFit = width;
        }
    }

    if (keepCountForLargestKnownToFit == 0) {
        keepCountForLargestKnownToFit = 1;
    }

    if (keepCount != keepCountForLargestKnownToFit) {
        keepCount = keepCountForLargestKnownToFit;
        truncatedLength = truncateToBuffer(string, length, keepCount, stringBuffer);
    }

    return String(stringBuffer, truncatedLength);
}

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

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

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

} // namespace WebCore