uniscribehelper.h

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// A wrapper around Uniscribe that provides a reasonable API.

#ifndef UniscribeHelper_h
#define UniscribeHelper_h

#include <windows.h>
#include <usp10.h>
#include <map>

#include <unicode/uchar.h>
#include <wtf/Vector.h>

class UniscribeTest_TooBig_Test;  // A gunit test for UniscribeHelper.

namespace WebCore {

class GraphicsContext;

#define UNISCRIBE_HELPER_STACK_RUNS 8
#define UNISCRIBE_HELPER_STACK_CHARS 32

// This object should be safe to create & destroy frequently, as long as the
// caller preserves the script_cache when possible (this data may be slow to
// compute).
//
// This object is "kind of large" (~1K) because it reserves a lot of space for
// working with to avoid expensive heap operations. Therefore, not only should
// you not worry about creating and destroying it, you should try to not keep
// them around.
class UniscribeHelper {
public:
    // Initializes this Uniscribe run with the text pointed to by |run| with
    // |length|. The input is NOT null terminated.
    //
    // The is_rtl flag should be set if the input script is RTL. It is assumed
    // that the caller has already divided up the input text (using ICU, for
    // example) into runs of the same direction of script. This avoids
    // disagreements between the caller and Uniscribe later (see FillItems).
    //
    // A script cache should be provided by the caller that is initialized to
    // NULL. When the caller is done with the cache (it may be stored between
    // runs as long as it is used consistently with the same HFONT), it should
    // call ScriptFreeCache().
    UniscribeHelper(const UChar* input,
                    int inputLength,
                    bool isRtl,
                    HFONT,
                    SCRIPT_CACHE*,
                    SCRIPT_FONTPROPERTIES*);

    virtual ~UniscribeHelper();

    // Sets Uniscribe's directional override flag. False by default.
    bool directionalOverride() const
    {
        return m_directionalOverride;
    }
    void setDirectionalOverride(bool override)
    {
        m_directionalOverride = override;
    }

    // Set's Uniscribe's no-ligate override flag. False by default.
    bool inhibitLigate() const
    {
        return m_inhibitLigate;
    }
    void setInhibitLigate(bool inhibit)
    {
        m_inhibitLigate = inhibit;
    }

    // Set letter spacing. We will try to insert this much space between
    // graphemes (one or more glyphs perceived as a single unit by ordinary
    // users of a script). Positive values increase letter spacing, negative
    // values decrease it. 0 by default.
    int letterSpacing() const
    {
        return m_letterSpacing;
    }
    void setLetterSpacing(int letterSpacing)
    {
        m_letterSpacing = letterSpacing;
    }

    // Set the width of a standard space character. We use this to normalize
    // space widths. Windows will make spaces after Hindi characters larger than
    // other spaces. A space_width of 0 means to use the default space width.
    //
    // Must be set before Init() is called.
    int spaceWidth() const
    {
        return m_spaceWidth;
    }
    void setSpaceWidth(int spaceWidth)
    {
        m_spaceWidth = spaceWidth;
    }

    // Set word spacing. We will try to insert this much extra space between
    // each word in the input (beyond whatever whitespace character separates
    // words). Positive values lead to increased letter spacing, negative values
    // decrease it. 0 by default.
    //
    // Must be set before Init() is called.
    int wordSpacing() const
    {
        return m_wordSpacing;
    }
    void setWordSpacing(int wordSpacing)
    {
        m_wordSpacing = wordSpacing;
    }

    void setAscent(int ascent)
    {
        m_ascent = ascent;
    }

    // When set to true, this class is used only to look up glyph
    // indices for a range of Unicode characters without glyph placement.
    // By default, it's false. This should be set to true when this
    // class is used for glyph index look-up for non-BMP characters
    // in GlyphPageNodeChromiumWin.cpp.
    void setDisableFontFallback(bool disableFontFallback)
    {
        m_disableFontFallback = true;
    }

    // You must call this after setting any options but before doing any
    // other calls like asking for widths or drawing.
    void init()
    {
        initWithOptionalLengthProtection(true);
    }

    // Returns the total width in pixels of the text run.
    int width() const;

    // Call to justify the text, with the amount of space that should be ADDED
    // to get the desired width that the column should be justified to.
    // Normally, spaces are inserted, but for Arabic there will be kashidas
    // (extra strokes) inserted instead.
    //
    // This function MUST be called AFTER Init().
    void justify(int additionalSpace);

    // Computes the given character offset into a pixel offset of the beginning
    // of that character.
    int characterToX(int offset) const;

    // Converts the given pixel X position into a logical character offset into
    // the run. For positions appearing before the first character, this will
    // return -1.
    int xToCharacter(int x) const;

    // Draws the given characters to (x, y) in the given DC. The font will be
    // handled by this function, but the font color and other attributes should
    // be pre-set.
    //
    // The y position is the upper left corner, NOT the baseline.
    void draw(GraphicsContext* graphicsContext, HDC dc, int x, int y, int from,
              int to);

    // Returns the first glyph assigned to the character at the given offset.
    // This function is used to retrieve glyph information when Uniscribe is
    // being used to generate glyphs for non-complex, non-BMP (above U+FFFF)
    // characters. These characters are not otherwise special and have no
    // complex shaping rules, so we don't otherwise need Uniscribe, except
    // Uniscribe is the only way to get glyphs for non-BMP characters.
    //
    // Returns 0 if there is no glyph for the given character.
    WORD firstGlyphForCharacter(int charOffset) const;

protected:
    // Backend for init. The flag allows the unit test to specify whether we
    // should fail early for very long strings like normal, or try to pass the
    // long string to Uniscribe. The latter provides a way to force failure of