root/Source/platform/fonts/skia/SimpleFontDataSkia.cpp

DEFINITIONS

1. platformInit
2. platformCharWidthInit
3. platformDestroy
4. platformCreateScaledFontData
5. determinePitch
6. getSkiaBoundsForGlyph
7. platformBoundsForGlyph
8. platformWidthForGlyph
9. canRenderCombiningCharacterSequence

/*
 * Copyright (c) 2008, 2009, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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#include "config.h"
#include "platform/fonts/SimpleFontData.h"

#include <unicode/normlzr.h>
#include "SkPaint.h"
#include "SkPath.h"
#include "SkTypeface.h"
#include "SkTypes.h"
#include "platform/fonts/FontDescription.h"
#include "platform/fonts/VDMXParser.h"
#include "platform/geometry/FloatRect.h"
#include "wtf/unicode/Unicode.h"

namespace WebCore {

// This is the largest VDMX table which we'll try to load and parse.
static const size_t maxVDMXTableSize = 1024 * 1024; // 1 MB

void SimpleFontData::platformInit()
{
    if (!m_platformData.size()) {
        m_fontMetrics.reset();
        m_avgCharWidth = 0;
        m_maxCharWidth = 0;
        return;
    }

    SkPaint paint;
    SkPaint::FontMetrics metrics;

    m_platformData.setupPaint(&paint);
    paint.getFontMetrics(&metrics);
    SkTypeface* face = paint.getTypeface();
    ASSERT(face);

    int vdmxAscent = 0, vdmxDescent = 0;
    bool isVDMXValid = false;

#if OS(LINUX) || OS(ANDROID)
    // Manually digging up VDMX metrics is only applicable when bytecode hinting using FreeType.
    // With GDI, the metrics will already have taken this into account (as needed).
    // With DirectWrite or CoreText, no bytecode hinting is ever done.
    // This code should be pushed into FreeType (hinted font metrics).
    static const uint32_t vdmxTag = SkSetFourByteTag('V', 'D', 'M', 'X');
    int pixelSize = m_platformData.size() + 0.5;
    if (!paint.isAutohinted()
        &&    (paint.getHinting() == SkPaint::kFull_Hinting
            || paint.getHinting() == SkPaint::kNormal_Hinting))
    {
        size_t vdmxSize = face->getTableSize(vdmxTag);
        if (vdmxSize && vdmxSize < maxVDMXTableSize) {
            uint8_t* vdmxTable = (uint8_t*) fastMalloc(vdmxSize);
            if (vdmxTable
                && face->getTableData(vdmxTag, 0, vdmxSize, vdmxTable) == vdmxSize
                && parseVDMX(&vdmxAscent, &vdmxDescent, vdmxTable, vdmxSize, pixelSize))
                isVDMXValid = true;
            fastFree(vdmxTable);
        }
    }
#endif

    float ascent;
    float descent;

    // Beware those who step here: This code is designed to match Win32 font
    // metrics *exactly* (except the adjustment of ascent/descent on Linux/Android).
    if (isVDMXValid) {
        ascent = vdmxAscent;
        descent = -vdmxDescent;
    } else {
        ascent = SkScalarRoundToInt(-metrics.fAscent);
        descent = SkScalarRoundToInt(metrics.fDescent);
#if OS(LINUX) || OS(ANDROID)
        // When subpixel positioning is enabled, if the descent is rounded down, the descent part
        // of the glyph may be truncated when displayed in a 'overflow: hidden' container.
        // To avoid that, borrow 1 unit from the ascent when possible.
        // FIXME: This can be removed if sub-pixel ascent/descent is supported.
        if (platformData().fontRenderStyle().useSubpixelPositioning && descent < SkScalarToFloat(metrics.fDescent) && ascent >= 1) {
            ++descent;
            --ascent;
        }
#endif
    }

    m_fontMetrics.setAscent(ascent);
    m_fontMetrics.setDescent(descent);

    float xHeight;
    if (metrics.fXHeight) {
        xHeight = metrics.fXHeight;
        m_fontMetrics.setXHeight(xHeight);
    } else {
        xHeight = ascent * 0.56; // Best guess from Windows font metrics.
        m_fontMetrics.setXHeight(xHeight);
        m_fontMetrics.setHasXHeight(false);
    }

    float lineGap = SkScalarToFloat(metrics.fLeading);
    m_fontMetrics.setLineGap(lineGap);
    m_fontMetrics.setLineSpacing(lroundf(ascent) + lroundf(descent) + lroundf(lineGap));

    // For now Skia does not support underline Thickness, once patch is comitted we can uncomment following
    // code, till then setting Underline Thickness to Zero so that default calculation is done.
    // float underlineThickness = SkScalarToFloat(metrics.fUnderlineThickness);
    // m_fontMetrics.setUnderlineThickness(underlineThickness);
    m_fontMetrics.setUnderlineThickness(0.f);

    if (platformData().orientation() == Vertical && !isTextOrientationFallback()) {
        static const uint32_t vheaTag = SkSetFourByteTag('v', 'h', 'e', 'a');
        static const uint32_t vorgTag = SkSetFourByteTag('V', 'O', 'R', 'G');
        size_t vheaSize = face->getTableSize(vheaTag);
        size_t vorgSize = face->getTableSize(vorgTag);
        if ((vheaSize > 0) || (vorgSize > 0))
            m_hasVerticalGlyphs = true;
    }

    // In WebKit/WebCore/platform/graphics/SimpleFontData.cpp, m_spaceWidth is
    // calculated for us, but we need to calculate m_maxCharWidth and
    // m_avgCharWidth in order for text entry widgets to be sized correctly.
#if OS(WIN)
    m_maxCharWidth = SkScalarRoundToInt(metrics.fMaxCharWidth);
#else
    // FIXME: This seems incorrect and should probably use fMaxCharWidth as
    // the code path above.
    SkScalar xRange = metrics.fXMax - metrics.fXMin;
    m_maxCharWidth = SkScalarRoundToInt(xRange * SkScalarRoundToInt(m_platformData.size()));
#endif

    if (metrics.fAvgCharWidth)
        m_avgCharWidth = SkScalarRoundToInt(metrics.fAvgCharWidth);
    else {
        m_avgCharWidth = xHeight;

        GlyphPage* glyphPageZero = GlyphPageTreeNode::getRootChild(this, 0)->page();

        if (glyphPageZero) {
            static const UChar32 xChar = 'x';
            const Glyph xGlyph = glyphPageZero->glyphForCharacter(xChar);

            if (xGlyph) {
                // In widthForGlyph(), xGlyph will be compared with
                // m_zeroWidthSpaceGlyph, which isn't initialized yet here.
                // Initialize it with zero to make sure widthForGlyph() returns
                // the right width.
                m_zeroWidthSpaceGlyph = 0;
                m_avgCharWidth = widthForGlyph(xGlyph);
            }
        }
    }

    if (int unitsPerEm = face->getUnitsPerEm())
        m_fontMetrics.setUnitsPerEm(unitsPerEm);
}

void SimpleFontData::platformCharWidthInit()
{
    // charwidths are set in platformInit.
}

void SimpleFontData::platformDestroy()
{
}

PassRefPtr<SimpleFontData> SimpleFontData::platformCreateScaledFontData(const FontDescription& fontDescription, float scaleFactor) const
{
    const float scaledSize = lroundf(fontDescription.computedSize() * scaleFactor);
    return SimpleFontData::create(FontPlatformData(m_platformData, scaledSize), isCustomFont() ? CustomFontData::create() : nullptr);
}

void SimpleFontData::determinePitch()
{
    m_treatAsFixedPitch = platformData().isFixedPitch();
}

static inline void getSkiaBoundsForGlyph(SkPaint& paint, Glyph glyph, SkRect& bounds)
{
    paint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);

    SkPath path;
    paint.getTextPath(&glyph, sizeof(glyph), 0, 0, &path);
    bounds = path.getBounds();

    if (!paint.isSubpixelText()) {
        SkIRect ir;
        bounds.round(&ir);
        bounds.set(ir);
    }
}

FloatRect SimpleFontData::platformBoundsForGlyph(Glyph glyph) const
{
    if (!m_platformData.size())
        return FloatRect();

    SkASSERT(sizeof(glyph) == 2); // compile-time assert

    SkPaint paint;
    m_platformData.setupPaint(&paint);

    SkRect bounds;
    getSkiaBoundsForGlyph(paint, glyph, bounds);
    return FloatRect(bounds);
}

float SimpleFontData::platformWidthForGlyph(Glyph glyph) const
{
    if (!m_platformData.size())
        return 0;

    SkASSERT(sizeof(glyph) == 2); // compile-time assert

    SkPaint paint;

    m_platformData.setupPaint(&paint);

    paint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
    SkScalar width = paint.measureText(&glyph, 2);
    if (!paint.isSubpixelText())
        width = SkScalarRoundToInt(width);
    return SkScalarToFloat(width);
}

#if USE(HARFBUZZ)
bool SimpleFontData::canRenderCombiningCharacterSequence(const UChar* characters, size_t length) const
{
    if (!m_combiningCharacterSequenceSupport)
        m_combiningCharacterSequenceSupport = adoptPtr(new HashMap<String, bool>);

    WTF::HashMap<String, bool>::AddResult addResult = m_combiningCharacterSequenceSupport->add(String(characters, length), false);
    if (!addResult.isNewEntry)
        return addResult.storedValue->value;

    UErrorCode error = U_ZERO_ERROR;
    Vector<UChar, 4> normalizedCharacters(length);
    int32_t normalizedLength = unorm_normalize(characters, length, UNORM_NFC, UNORM_UNICODE_3_2, &normalizedCharacters[0], length, &error);
    // Can't render if we have an error or no composition occurred.
    if (U_FAILURE(error) || (static_cast<size_t>(normalizedLength) == length))
        return false;

    SkPaint paint;
    m_platformData.setupPaint(&paint);
    paint.setTextEncoding(SkPaint::kUTF16_TextEncoding);
    if (paint.textToGlyphs(&normalizedCharacters[0], normalizedLength * 2, 0)) {
        addResult.storedValue->value = true;
        return true;
    }
    return false;
}
#endif

} // namespace WebCore