Rearrange storage of reserved tracks for railway tiles

[openttd/fttd.git] / src / gfx_layout.cpp

/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file gfx_layout.cpp Handling of laying out text. */

#include "stdafx.h"
#include "gfx_layout.h"
#include "string_func.h"
#include "strings_func.h"
#include "debug.h"

#include "table/control_codes.h"

#ifdef WITH_ICU
#include <unicode/ustring.h>
#endif /* WITH_ICU */


/** Cache of ParagraphLayout lines. */
Layouter::LineCache *Layouter::linecache;

/** Cache of Font instances. */
Layouter::FontColourMap Layouter::fonts[FS_END];


/**
 * Construct a new font.
 * @param size   The font size to use for this font.
 * @param colour The colour to draw this font in.
 */
Font::Font(FontSize size, TextColour colour) :
                fc(FontCache::Get(size)), colour(colour)
{
        assert(size < FS_END);
}

#ifdef WITH_ICU
/* Implementation details of LEFontInstance */

le_int32 Font::getUnitsPerEM() const
{
        return this->fc->GetUnitsPerEM();
}

le_int32 Font::getAscent() const
{
        return this->fc->GetAscender();
}

le_int32 Font::getDescent() const
{
        return -this->fc->GetDescender();
}

le_int32 Font::getLeading() const
{
        return this->fc->GetHeight();
}

float Font::getXPixelsPerEm() const
{
        return (float)this->fc->GetHeight();
}

float Font::getYPixelsPerEm() const
{
        return (float)this->fc->GetHeight();
}

float Font::getScaleFactorX() const
{
        return 1.0f;
}

float Font::getScaleFactorY() const
{
        return 1.0f;
}

const void *Font::getFontTable(LETag tableTag) const
{
        size_t length;
        return this->getFontTable(tableTag, length);
}

const void *Font::getFontTable(LETag tableTag, size_t &length) const
{
        return this->fc->GetFontTable(tableTag, length);
}

LEGlyphID Font::mapCharToGlyph(LEUnicode32 ch) const
{
        if (IsTextDirectionChar(ch)) return 0;
        return this->fc->MapCharToGlyph(ch);
}

void Font::getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const
{
        advance.fX = glyph == 0xFFFF ? 0 : this->fc->GetGlyphWidth(glyph);
        advance.fY = 0;
}

le_bool Font::getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const
{
        return FALSE;
}

static size_t AppendToBuffer(UChar *buff, const UChar *buffer_last, WChar c)
{
        /* Transform from UTF-32 to internal ICU format of UTF-16. */
        int32 length = 0;
        UErrorCode err = U_ZERO_ERROR;
        u_strFromUTF32(buff, buffer_last - buff, &length, (UChar32*)&c, 1, &err);
        return length;
}

/**
 * Wrapper for doing layouts with ICU.
 */
class ICUParagraphLayout : public AutoDeleteSmallVector<ParagraphLayouter::Line *, 4>, public ParagraphLayouter {
        ParagraphLayout *p; ///< The actual ICU paragraph layout.
public:
        /** Helper for GetLayouter, to get the right type. */
        typedef UChar CharType;
        /** Helper for GetLayouter, to get whether the layouter supports RTL. */
        static const bool SUPPORTS_RTL = true;

        /** Visual run contains data about the bit of text with the same font. */
        class ICUVisualRun : public ParagraphLayouter::VisualRun {
                const ParagraphLayout::VisualRun *vr; ///< The actual ICU vr.

        public:
                ICUVisualRun(const ParagraphLayout::VisualRun *vr) : vr(vr) { }

                const Font *GetFont() const          { return (const Font*)vr->getFont(); }
                int GetGlyphCount() const            { return vr->getGlyphCount(); }
                const GlyphID *GetGlyphs() const     { return vr->getGlyphs(); }
                const float *GetPositions() const    { return vr->getPositions(); }
                int GetLeading() const               { return vr->getLeading(); }
                const int *GetGlyphToCharMap() const { return vr->getGlyphToCharMap(); }
        };

        /** A single line worth of VisualRuns. */
        class ICULine : public AutoDeleteSmallVector<ICUVisualRun *, 4>, public ParagraphLayouter::Line {
                ParagraphLayout::Line *l; ///< The actual ICU line.

        public:
                ICULine(ParagraphLayout::Line *l) : l(l)
                {
                        for (int i = 0; i < l->countRuns(); i++) {
                                *this->Append() = new ICUVisualRun(l->getVisualRun(i));
                        }
                }
                ~ICULine() { delete l; }

                int GetLeading() const { return l->getLeading(); }
                int GetWidth() const   { return l->getWidth(); }
                int CountRuns() const  { return l->countRuns(); }
                const ParagraphLayouter::VisualRun *GetVisualRun(int run) const { return *this->Get(run); }

                int GetInternalCharLength(WChar c) const
                {
                        /* ICU uses UTF-16 internally which means we need to account for surrogate pairs. */
                        return Utf8CharLen(c) < 4 ? 1 : 2;
                }
        };

        ICUParagraphLayout(ParagraphLayout *p) : p(p) { }
        ~ICUParagraphLayout() { delete p; }
        void Reflow() { p->reflow(); }

        ParagraphLayouter::Line *NextLine(int max_width)
        {
                ParagraphLayout::Line *l = p->nextLine(max_width);
                return l == NULL ? NULL : new ICULine(l);
        }
};

static ParagraphLayouter *GetParagraphLayout(UChar *buff, UChar *buff_end, FontMap &fontMapping)
{
        int32 length = buff_end - buff;

        if (length == 0) {
                /* ICU's ParagraphLayout cannot handle empty strings, so fake one. */
                buff[0] = ' ';
                length = 1;
                fontMapping.End()[-1].first++;
        }

        /* Fill ICU's FontRuns with the right data. */
        FontRuns runs(fontMapping.Length());
        for (FontMap::iterator iter = fontMapping.Begin(); iter != fontMapping.End(); iter++) {
                runs.add(iter->second, iter->first);
        }

        LEErrorCode status = LE_NO_ERROR;
        /* ParagraphLayout does not copy "buff", so it must stay valid.
         * "runs" is copied according to the ICU source, but the documentation does not specify anything, so this might break somewhen. */
        ParagraphLayout *p = new ParagraphLayout(buff, length, &runs, NULL, NULL, NULL, _current_text_dir == TD_RTL ? UBIDI_DEFAULT_RTL : UBIDI_DEFAULT_LTR, false, status);
        if (status != LE_NO_ERROR) {
                delete p;
                return NULL;
        }

        return new ICUParagraphLayout(p);
}

#endif /* WITH_ICU */

/*** Paragraph layout ***/
/**
 * Class handling the splitting of a paragraph of text into lines and
 * visual runs.
 *
 * One constructs this class with the text that needs to be split into
 * lines. Then nextLine is called with the maximum width until NULL is
 * returned. Each nextLine call creates VisualRuns which contain the
 * length of text that are to be drawn with the same font. In other
 * words, the result of this class is a list of sub strings with their
 * font. The sub strings are then already fully laid out, and only
 * need actual drawing.
 *
 * The positions in a visual run are sequential pairs of X,Y of the
 * begin of each of the glyphs plus an extra pair to mark the end.
 *
 * @note This variant does not handle left-to-right properly. This
 *       is supported in the one ParagraphLayout coming from ICU.
 */
class FallbackParagraphLayout : public ParagraphLayouter {
public:
        /** Helper for GetLayouter, to get the right type. */
        typedef WChar CharType;
        /** Helper for GetLayouter, to get whether the layouter supports RTL. */
        static const bool SUPPORTS_RTL = false;

        /** Visual run contains data about the bit of text with the same font. */
        class FallbackVisualRun : public ParagraphLayouter::VisualRun {
                Font *font;       ///< The font used to layout these.
                GlyphID *glyphs;  ///< The glyphs we're drawing.
                float *positions; ///< The positions of the glyphs.
                int *glyph_to_char; ///< The char index of the glyphs.
                int glyph_count;  ///< The number of glyphs.

        public:
                FallbackVisualRun(Font *font, const WChar *chars, int glyph_count, int x);
                ~FallbackVisualRun();
                const Font *GetFont() const;
                int GetGlyphCount() const;
                const GlyphID *GetGlyphs() const;
                const float *GetPositions() const;
                int GetLeading() const;
                const int *GetGlyphToCharMap() const;
        };

        /** A single line worth of VisualRuns. */
        class FallbackLine : public AutoDeleteSmallVector<FallbackVisualRun *, 4>, public ParagraphLayouter::Line {
        public:
                int GetLeading() const;
                int GetWidth() const;
                int CountRuns() const;
                const ParagraphLayouter::VisualRun *GetVisualRun(int run) const;

                int GetInternalCharLength(WChar c) const { return 1; }
        };

        const WChar *buffer_begin; ///< Begin of the buffer.
        const WChar *buffer;       ///< The current location in the buffer.
        FontMap &runs;             ///< The fonts we have to use for this paragraph.

        FallbackParagraphLayout(WChar *buffer, int length, FontMap &runs);
        void Reflow();
        const ParagraphLayouter::Line *NextLine(int max_width);
};

/**
 * Create the visual run.
 * @param font       The font to use for this run.
 * @param chars      The characters to use for this run.
 * @param char_count The number of characters in this run.
 * @param x          The initial x position for this run.
 */
FallbackParagraphLayout::FallbackVisualRun::FallbackVisualRun(Font *font, const WChar *chars, int char_count, int x) :
                font(font), glyph_count(char_count)
{
        this->glyphs = MallocT<GlyphID>(this->glyph_count);
        this->glyph_to_char = MallocT<int>(this->glyph_count);

        /* Positions contains the location of the begin of each of the glyphs, and the end of the last one. */
        this->positions = MallocT<float>(this->glyph_count * 2 + 2);
        this->positions[0] = x;
        this->positions[1] = 0;

        for (int i = 0; i < this->glyph_count; i++) {
                this->glyphs[i] = font->fc->MapCharToGlyph(chars[i]);
                this->positions[2 * i + 2] = this->positions[2 * i] + font->fc->GetGlyphWidth(this->glyphs[i]);
                this->positions[2 * i + 3] = 0;
                this->glyph_to_char[i] = i;
        }
}

/** Free all data. */
FallbackParagraphLayout::FallbackVisualRun::~FallbackVisualRun()
{
        free(this->positions);
        free(this->glyph_to_char);
        free(this->glyphs);
}

/**
 * Get the font associated with this run.
 * @return The font.
 */
const Font *FallbackParagraphLayout::FallbackVisualRun::GetFont() const
{
        return this->font;
}

/**
 * Get the number of glyphs in this run.
 * @return The number of glyphs.
 */
int FallbackParagraphLayout::FallbackVisualRun::GetGlyphCount() const
{
        return this->glyph_count;
}

/**
 * Get the glyphs of this run.
 * @return The glyphs.
 */
const GlyphID *FallbackParagraphLayout::FallbackVisualRun::GetGlyphs() const
{
        return this->glyphs;
}

/**
 * Get the positions of this run.
 * @return The positions.
 */
const float *FallbackParagraphLayout::FallbackVisualRun::GetPositions() const
{
        return this->positions;
}

/**
 * Get the glyph-to-character map for this visual run.
 * @return The glyph-to-character map.
 */
const int *FallbackParagraphLayout::FallbackVisualRun::GetGlyphToCharMap() const
{
        return this->glyph_to_char;
}

/**
 * Get the height of this font.
 * @return The height of the font.
 */
int FallbackParagraphLayout::FallbackVisualRun::GetLeading() const
{
        return this->GetFont()->fc->GetHeight();
}

/**
 * Get the height of the line.
 * @return The maximum height of the line.
 */
int FallbackParagraphLayout::FallbackLine::GetLeading() const
{
        int leading = 0;
        for (const FallbackVisualRun * const *run = this->Begin(); run != this->End(); run++) {
                leading = max(leading, (*run)->GetLeading());
        }

        return leading;
}

/**
 * Get the width of this line.
 * @return The width of the line.
 */
int FallbackParagraphLayout::FallbackLine::GetWidth() const
{
        if (this->Length() == 0) return 0;

        /*
         * The last X position of a run contains is the end of that run.
         * Since there is no left-to-right support, taking this value of
         * the last run gives us the end of the line and thus the width.
         */
        const ParagraphLayouter::VisualRun *run = this->GetVisualRun(this->CountRuns() - 1);
        return (int)run->GetPositions()[run->GetGlyphCount() * 2];
}

/**
 * Get the number of runs in this line.
 * @return The number of runs.
 */
int FallbackParagraphLayout::FallbackLine::CountRuns() const
{
        return this->Length();
}

/**
 * Get a specific visual run.
 * @return The visual run.
 */
const ParagraphLayouter::VisualRun *FallbackParagraphLayout::FallbackLine::GetVisualRun(int run) const
{
        return *this->Get(run);
}

/**
 * Create a new paragraph layouter.
 * @param buffer The characters of the paragraph.
 * @param length The length of the paragraph.
 * @param runs   The font mapping of this paragraph.
 */
FallbackParagraphLayout::FallbackParagraphLayout(WChar *buffer, int length, FontMap &runs) : buffer_begin(buffer), buffer(buffer), runs(runs)
{
        assert(runs.End()[-1].first == length);
}

/**
 * Reset the position to the start of the paragraph.
 */
void FallbackParagraphLayout::Reflow()
{
        this->buffer = this->buffer_begin;
}

/**
 * Construct a new line with a maximum width.
 * @param max_width The maximum width of the string.
 * @return A Line, or NULL when at the end of the paragraph.
 */
const ParagraphLayouter::Line *FallbackParagraphLayout::NextLine(int max_width)
{
        /* Simple idea:
         *  - split a line at a newline character, or at a space where we can break a line.
         *  - split for a visual run whenever a new line happens, or the font changes.
         */
        if (this->buffer == NULL) return NULL;

        FallbackLine *l = new FallbackLine();

        if (*this->buffer == '\0') {
                /* Only a newline. */
                this->buffer = NULL;
                *l->Append() = new FallbackVisualRun(this->runs.Begin()->second, this->buffer, 0, 0);
                return l;
        }

        const WChar *begin = this->buffer;
        const WChar *last_space = NULL;
        const WChar *last_char = begin;
        int width = 0;

        int offset = this->buffer - this->buffer_begin;
        FontMap::iterator iter = this->runs.Begin();
        while (iter->first <= offset) {
                iter++;
                assert(iter != this->runs.End());
        }

        const FontCache *fc = iter->second->fc;
        const WChar *next_run = this->buffer_begin + iter->first;

        for (;;) {
                WChar c = *this->buffer;
                last_char = this->buffer;

                if (c == '\0') {
                        this->buffer = NULL;
                        break;
                }

                if (this->buffer == next_run) {
                        int w = l->GetWidth();
                        *l->Append() = new FallbackVisualRun(iter->second, begin, this->buffer - begin, w);
                        iter++;
                        assert(iter != this->runs.End());

                        next_run = this->buffer_begin + iter->first;
                        begin = this->buffer;

                        last_space = NULL;
                }

                if (IsWhitespace(c)) last_space = this->buffer;

                if (IsPrintable(c) && !IsTextDirectionChar(c)) {
                        int char_width = GetCharacterWidth(fc->GetSize(), c);
                        width += char_width;
                        if (width > max_width) {
                                /* The string is longer than maximum width so we need to decide
                                 * what to do with it. */
                                if (width == char_width) {
                                        /* The character is wider than allowed width; don't know
                                         * what to do with this case... bail out! */
                                        this->buffer = NULL;
                                        return l;
                                }

                                if (last_space == NULL) {
                                        /* No space has been found. Just terminate at our current
                                         * location. This usually happens for languages that do not
                                         * require spaces in strings, like Chinese, Japanese and
                                         * Korean. For other languages terminating mid-word might
                                         * not be the best, but terminating the whole string instead
                                         * of continuing the word at the next line is worse. */
                                        last_char = this->buffer;
                                } else {
                                        /* A space is found; perfect place to terminate */
                                        this->buffer = last_space + 1;
                                        last_char = last_space;
                                }
                                break;
                        }
                }

                this->buffer++;
        }

        if (l->Length() == 0 || last_char - begin != 0) {
                int w = l->GetWidth();
                *l->Append() = new FallbackVisualRun(iter->second, begin, last_char - begin, w);
        }
        return l;
}

/**
 * Appand a wide character to the internal buffer.
 * @param buff        The buffer to append to.
 * @param buffer_last The end of the buffer.
 * @param c           The character to add.
 * @return The number of buffer spaces that were used.
 */
static size_t AppendToBuffer(WChar *buff, const WChar *buffer_last, WChar c)
{
        *buff = c;
        return 1;
}

/**
 * Get the actual ParagraphLayout for the given buffer.
 * @param buff The begin of the buffer.
 * @param buff_end The location after the last element in the buffer.
 * @param fontMapping THe mapping of the fonts.
 * @return The ParagraphLayout instance.
 */
static FallbackParagraphLayout *GetParagraphLayout(WChar *buff, WChar *buff_end, FontMap &fontMapping)
{
        return new FallbackParagraphLayout(buff, buff_end - buff, fontMapping);
}

/**
 * Helper for getting a ParagraphLayouter of the given type.
 *
 * @note In case no ParagraphLayouter could be constructed, line.layout will be NULL.
 * @param line The cache item to store our layouter in.
 * @param str The string to create a layouter for.
 * @param state The state of the font and color.
 * @tparam T The type of layouter we want.
 */
template <typename T>
static inline void GetLayouter(Layouter::LineCacheItem &line, const char *&str, FontState &state)
{
        if (line.buffer != NULL) free(line.buffer);

        typename T::CharType *buff_begin = MallocT<typename T::CharType>(DRAW_STRING_BUFFER);
        const typename T::CharType *buffer_last = buff_begin + DRAW_STRING_BUFFER;
        typename T::CharType *buff = buff_begin;
        FontMap &fontMapping = line.runs;
        Font *f = Layouter::GetFont(state.fontsize, state.cur_colour);

        line.buffer = buff_begin;

        /*
         * Go through the whole string while adding Font instances to the font map
         * whenever the font changes, and convert the wide characters into a format
         * usable by ParagraphLayout.
         */
        for (; buff < buffer_last;) {
                WChar c = Utf8Consume(const_cast<const char **>(&str));
                if (c == '\0' || c == '\n') {
                        break;
                } else if (c >= SCC_BLUE && c <= SCC_BLACK) {
                        state.SetColour((TextColour)(c - SCC_BLUE));
                } else if (c == SCC_PREVIOUS_COLOUR) { // Revert to the previous colour.
                        state.SetPreviousColour();
                } else if (c == SCC_TINYFONT) {
                        state.SetFontSize(FS_SMALL);
                } else if (c == SCC_BIGFONT) {
                        state.SetFontSize(FS_LARGE);
                } else {
                        /* Filter out text direction characters that shouldn't be drawn, and
                         * will not be handled in the fallback non ICU case because they are
                         * mostly needed for RTL languages which need more ICU support. */
                        if (!T::SUPPORTS_RTL && IsTextDirectionChar(c)) continue;
                        buff += AppendToBuffer(buff, buffer_last, c);
                        continue;
                }

                if (!fontMapping.Contains(buff - buff_begin)) {
                        fontMapping.Insert(buff - buff_begin, f);
                }
                f = Layouter::GetFont(state.fontsize, state.cur_colour);
        }

        /* Better safe than sorry. */
        *buff = '\0';

        if (!fontMapping.Contains(buff - buff_begin)) {
                fontMapping.Insert(buff - buff_begin, f);
        }
        line.layout = GetParagraphLayout(buff_begin, buff, fontMapping);
        line.state_after = state;
}

/**
 * Create a new layouter.
 * @param str      The string to create the layout for.
 * @param maxw     The maximum width.
 * @param colour   The colour of the font.
 * @param fontsize The size of font to use.
 */
Layouter::Layouter(const char *str, int maxw, TextColour colour, FontSize fontsize) : string(str)
{
        FontState state(colour, fontsize);
        WChar c = 0;

        do {
                /* Scan string for end of line */
                const char *lineend = str;
                for (;;) {
                        size_t len = Utf8Decode(&c, lineend);
                        if (c == '\0' || c == '\n') break;
                        lineend += len;
                }

                LineCacheItem& line = GetCachedParagraphLayout(str, lineend - str, state);
                if (line.layout != NULL) {
                        /* Line is in cache */
                        str = lineend + 1;
                        state = line.state_after;
                        line.layout->Reflow();
                } else {
                        /* Line is new, layout it */
#ifdef WITH_ICU
                        FontState old_state = state;
                        const char *old_str = str;

                        GetLayouter<ICUParagraphLayout>(line, str, state);
                        if (line.layout == NULL) {
                                static bool warned = false;
                                if (!warned) {
                                        DEBUG(misc, 0, "ICU layouter bailed on the font. Falling back to the fallback layouter");
                                        warned = true;
                                }

                                state = old_state;
                                str = old_str;
                                GetLayouter<FallbackParagraphLayout>(line, str, state);
                        }
#else
                        GetLayouter<FallbackParagraphLayout>(line, str, state);
#endif
                }

                /* Copy all lines into a local cache so we can reuse them later on more easily. */
                const ParagraphLayouter::Line *l;
                while ((l = line.layout->NextLine(maxw)) != NULL) {
                        *this->Append() = l;
                }

        } while (c != '\0');
}

/**
 * Get the boundaries of this paragraph.
 * @return The boundaries.
 */
Dimension Layouter::GetBounds()
{
        Dimension d = { 0, 0 };
        for (const ParagraphLayouter::Line **l = this->Begin(); l != this->End(); l++) {
                d.width = max<uint>(d.width, (*l)->GetWidth());
                d.height += (*l)->GetLeading();
        }
        return d;
}

/**
 * Get the position of a character in the layout.
 * @param ch Character to get the position of.
 * @return Upper left corner of the character relative to the start of the string.
 * @note Will only work right for single-line strings.
 */
Point Layouter::GetCharPosition(const char *ch) const
{
        /* Find the code point index which corresponds to the char
         * pointer into our UTF-8 source string. */
        size_t index = 0;
        const char *str = this->string;
        while (str < ch) {
                WChar c;
                size_t len = Utf8Decode(&c, str);
                if (c == '\0' || c == '\n') break;
                str += len;
                index += (*this->Begin())->GetInternalCharLength(c);
        }

        if (str == ch) {
                /* Valid character. */
                const ParagraphLayouter::Line *line = *this->Begin();

                /* Pointer to the end-of-string/line marker? Return total line width. */
                if (*ch == '\0' || *ch == '\n') {
                        Point p = { line->GetWidth(), 0 };
                        return p;
                }

                /* Scan all runs until we've found our code point index. */
                for (int run_index = 0; run_index < line->CountRuns(); run_index++) {
                        const ParagraphLayouter::VisualRun *run = line->GetVisualRun(run_index);

                        for (int i = 0; i < run->GetGlyphCount(); i++) {
                                /* Matching glyph? Return position. */
                                if ((size_t)run->GetGlyphToCharMap()[i] == index) {
                                        Point p = { (int)run->GetPositions()[i * 2], (int)run->GetPositions()[i * 2 + 1] };
                                        return p;
                                }
                        }
                }
        }

        Point p = { 0, 0 };
        return p;
}

/**
 * Get the character that is at a position.
 * @param x Position in the string.
 * @return Pointer to the character at the position or NULL if no character is at the position.
 */
const char *Layouter::GetCharAtPosition(int x) const
{
        const ParagraphLayouter::Line *line = *this->Begin();

        for (int run_index = 0; run_index < line->CountRuns(); run_index++) {
                const ParagraphLayouter::VisualRun *run = line->GetVisualRun(run_index);

                for (int i = 0; i < run->GetGlyphCount(); i++) {
                        /* Not a valid glyph (empty). */
                        if (run->GetGlyphs()[i] == 0xFFFF) continue;

                        int begin_x = (int)run->GetPositions()[i * 2];
                        int end_x   = (int)run->GetPositions()[i * 2 + 2];

                        if (IsInsideMM(x, begin_x, end_x)) {
                                /* Found our glyph, now convert to UTF-8 string index. */
                                size_t index = run->GetGlyphToCharMap()[i];

                                size_t cur_idx = 0;
                                for (const char *str = this->string; *str != '\0'; ) {
                                        if (cur_idx == index) return str;

                                        WChar c = Utf8Consume(&str);
                                        cur_idx += line->GetInternalCharLength(c);
                                }
                        }
                }
        }

        return NULL;
}

/**
 * Get a static font instance.
 */
Font *Layouter::GetFont(FontSize size, TextColour colour)
{
        FontColourMap::iterator it = fonts[size].Find(colour);
        if (it != fonts[size].End()) return it->second;

        Font *f = new Font(size, colour);
        *fonts[size].Append() = FontColourMap::Pair(colour, f);
        return f;
}

/**
 * Reset cached font information.
 * @param size Font size to reset.
 */
void Layouter::ResetFontCache(FontSize size)
{
        for (FontColourMap::iterator it = fonts[size].Begin(); it != fonts[size].End(); ++it) {
                delete it->second;
        }
        fonts[size].Clear();

        /* We must reset the linecache since it references the just freed fonts */
        ResetLineCache();
}

/**
 * Get reference to cache item.
 * If the item does not exist yet, it is default constructed.
 * @param str Source string of the line (including colour and font size codes).
 * @param len Length of \a str in bytes (no termination).
 * @param state State of the font at the beginning of the line.
 * @return Reference to cache item.
 */
Layouter::LineCacheItem &Layouter::GetCachedParagraphLayout(const char *str, size_t len, const FontState &state)
{
        if (linecache == NULL) {
                /* Create linecache on first access to avoid trouble with initialisation order of static variables. */
                linecache = new LineCache();
        }

        LineCacheKey key;
        key.state_before = state;
        key.str.assign(str, len);
        return (*linecache)[key];
}

/**
 * Clear line cache.
 */
void Layouter::ResetLineCache()
{
        if (linecache != NULL) linecache->clear();
}

/**
 * Reduce the size of linecache if necessary to prevent infinite growth.
 */
void Layouter::ReduceLineCache()
{
        if (linecache != NULL) {
                /* TODO LRU cache would be fancy, but not exactly necessary */
                if (linecache->size() > 4096) ResetLineCache();
        }
}