DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (b6057e17f856)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "gfxFT2FontBase.h"
#include "gfxFT2Utils.h"
#include "mozilla/Likely.h"
#include FT_TRUETYPE_TAGS_H
#include FT_TRUETYPE_TABLES_H
#include <algorithm>

#ifdef HAVE_FONTCONFIG_FCFREETYPE_H
#include <fontconfig/fcfreetype.h>
#endif

#include "prlink.h"

// aScale is intended for a 16.16 x/y_scale of an FT_Size_Metrics
static inline FT_Long
ScaleRoundDesignUnits(FT_Short aDesignMetric, FT_Fixed aScale)
{
    FT_Long fixed26dot6 = FT_MulFix(aDesignMetric, aScale);
    return ROUND_26_6_TO_INT(fixed26dot6);
}

// Snap a line to pixels while keeping the center and size of the line as
// close to the original position as possible.
//
// Pango does similar snapping for underline and strikethrough when fonts are
// hinted, but nsCSSRendering::GetTextDecorationRectInternal always snaps the
// top and size of lines.  Optimizing the distance between the line and
// baseline is probably good for the gap between text and underline, but
// optimizing the center of the line is better for positioning strikethough.
static void
SnapLineToPixels(gfxFloat& aOffset, gfxFloat& aSize)
{
    gfxFloat snappedSize = std::max(floor(aSize + 0.5), 1.0);
    // Correct offset for change in size
    gfxFloat offset = aOffset - 0.5 * (aSize - snappedSize);
    // Snap offset
    aOffset = floor(offset + 0.5);
    aSize = snappedSize;
}

void
gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
                             uint32_t* aSpaceGlyph)
{
    NS_PRECONDITION(aMetrics != nullptr, "aMetrics must not be NULL");
    NS_PRECONDITION(aSpaceGlyph != nullptr, "aSpaceGlyph must not be NULL");

    if (MOZ_UNLIKELY(!mFace)) {
        // No face.  This unfortunate situation might happen if the font
        // file is (re)moved at the wrong time.
        const gfxFloat emHeight = mGfxFont->GetStyle()->size;
        aMetrics->emHeight = emHeight;
        aMetrics->maxAscent = aMetrics->emAscent = 0.8 * emHeight;
        aMetrics->maxDescent = aMetrics->emDescent = 0.2 * emHeight;
        aMetrics->maxHeight = emHeight;
        aMetrics->internalLeading = 0.0;
        aMetrics->externalLeading = 0.2 * emHeight;
        const gfxFloat spaceWidth = 0.5 * emHeight;
        aMetrics->spaceWidth = spaceWidth;
        aMetrics->maxAdvance = spaceWidth;
        aMetrics->aveCharWidth = spaceWidth;
        aMetrics->zeroOrAveCharWidth = spaceWidth;
        const gfxFloat xHeight = 0.5 * emHeight;
        aMetrics->xHeight = xHeight;
        aMetrics->superscriptOffset = xHeight;
        aMetrics->subscriptOffset = xHeight;
        const gfxFloat underlineSize = emHeight / 14.0;
        aMetrics->underlineSize = underlineSize;
        aMetrics->underlineOffset = -underlineSize;
        aMetrics->strikeoutOffset = 0.25 * emHeight;
        aMetrics->strikeoutSize = underlineSize;

        *aSpaceGlyph = 0;
        return;
    }

    const FT_Size_Metrics& ftMetrics = mFace->size->metrics;

    gfxFloat emHeight;
    // Scale for vertical design metric conversion: pixels per design unit.
    // If this remains at 0.0, we can't use metrics from OS/2 etc.
    gfxFloat yScale = 0.0;
    if (FT_IS_SCALABLE(mFace)) {
        // Prefer FT_Size_Metrics::x_scale to x_ppem as x_ppem does not
        // have subpixel accuracy.
        //
        // FT_Size_Metrics::y_scale is in 16.16 fixed point format.  Its
        // (fractional) value is a factor that converts vertical metrics from
        // design units to units of 1/64 pixels, so that the result may be
        // interpreted as pixels in 26.6 fixed point format.
        yScale = FLOAT_FROM_26_6(FLOAT_FROM_16_16(ftMetrics.y_scale));
        emHeight = mFace->units_per_EM * yScale;
    } else { // Not scalable.
        emHeight = ftMetrics.y_ppem;
        // FT_Face doc says units_per_EM and a bunch of following fields
        // are "only relevant to scalable outlines". If it's an sfnt,
        // we can get units_per_EM from the 'head' table instead; otherwise,
        // we don't have a unitsPerEm value so we can't compute/use yScale.
        const TT_Header* head =
            static_cast<TT_Header*>(FT_Get_Sfnt_Table(mFace, ft_sfnt_head));
        if (head) {
            gfxFloat emUnit = head->Units_Per_EM;
            yScale = emHeight / emUnit;
        }
    }

    TT_OS2 *os2 =
        static_cast<TT_OS2*>(FT_Get_Sfnt_Table(mFace, ft_sfnt_os2));

    aMetrics->maxAscent = FLOAT_FROM_26_6(ftMetrics.ascender);
    aMetrics->maxDescent = -FLOAT_FROM_26_6(ftMetrics.descender);
    aMetrics->maxAdvance = FLOAT_FROM_26_6(ftMetrics.max_advance);

    gfxFloat lineHeight;
    if (os2 && os2->sTypoAscender && yScale > 0.0) {
        aMetrics->emAscent = os2->sTypoAscender * yScale;
        aMetrics->emDescent = -os2->sTypoDescender * yScale;
        FT_Short typoHeight =
            os2->sTypoAscender - os2->sTypoDescender + os2->sTypoLineGap;
        lineHeight = typoHeight * yScale;

        // If the OS/2 fsSelection USE_TYPO_METRICS bit is set,
        // or if this is an OpenType Math font,
        // set maxAscent/Descent from the sTypo* fields instead of hhea.
        const uint16_t kUseTypoMetricsMask = 1 << 7;
        FT_ULong length = 0;
        if ((os2->fsSelection & kUseTypoMetricsMask) ||
            0 == FT_Load_Sfnt_Table(mFace, FT_MAKE_TAG('M','A','T','H'),
                                    0, nullptr, &length)) {
            aMetrics->maxAscent = NS_round(aMetrics->emAscent);
            aMetrics->maxDescent = NS_round(aMetrics->emDescent);
        } else {
            // maxAscent/maxDescent get used for frame heights, and some fonts
            // don't have the HHEA table ascent/descent set (bug 279032).
            // We use NS_round here to parallel the pixel-rounded values that
            // freetype gives us for ftMetrics.ascender/descender.
            aMetrics->maxAscent =
                std::max(aMetrics->maxAscent, NS_round(aMetrics->emAscent));
            aMetrics->maxDescent =
                std::max(aMetrics->maxDescent, NS_round(aMetrics->emDescent));
        }
    } else {
        aMetrics->emAscent = aMetrics->maxAscent;
        aMetrics->emDescent = aMetrics->maxDescent;
        lineHeight = FLOAT_FROM_26_6(ftMetrics.height);
    }

    cairo_text_extents_t extents;
    *aSpaceGlyph = GetCharExtents(' ', &extents);
    if (*aSpaceGlyph) {
        aMetrics->spaceWidth = extents.x_advance;
    } else {
        aMetrics->spaceWidth = aMetrics->maxAdvance; // guess
    }

    aMetrics->zeroOrAveCharWidth = 0.0;
    if (GetCharExtents('0', &extents)) {
        aMetrics->zeroOrAveCharWidth = extents.x_advance;
    }

    // Prefering a measured x over sxHeight because sxHeight doesn't consider
    // hinting, but maybe the x extents are not quite right in some fancy
    // script fonts.  CSS 2.1 suggests possibly using the height of an "o",
    // which would have a more consistent glyph across fonts.
    if (GetCharExtents('x', &extents) && extents.y_bearing < 0.0) {
        aMetrics->xHeight = -extents.y_bearing;
        aMetrics->aveCharWidth = extents.x_advance;
    } else {
        if (os2 && os2->sxHeight && yScale > 0.0) {
            aMetrics->xHeight = os2->sxHeight * yScale;
        } else {
            // CSS 2.1, section 4.3.2 Lengths: "In the cases where it is
            // impossible or impractical to determine the x-height, a value of
            // 0.5em should be used."
            aMetrics->xHeight = 0.5 * emHeight;
        }
        aMetrics->aveCharWidth = 0.0; // updated below
    }
    // aveCharWidth is used for the width of text input elements so be
    // liberal rather than conservative in the estimate.
    if (os2 && os2->xAvgCharWidth) {
        // Round to pixels as this is compared with maxAdvance to guess
        // whether this is a fixed width font.
        gfxFloat avgCharWidth =
            ScaleRoundDesignUnits(os2->xAvgCharWidth, ftMetrics.x_scale);
        aMetrics->aveCharWidth =
            std::max(aMetrics->aveCharWidth, avgCharWidth);
    }
    aMetrics->aveCharWidth =
        std::max(aMetrics->aveCharWidth, aMetrics->zeroOrAveCharWidth);
    if (aMetrics->aveCharWidth == 0.0) {
        aMetrics->aveCharWidth = aMetrics->spaceWidth;
    }
    if (aMetrics->zeroOrAveCharWidth == 0.0) {
        aMetrics->zeroOrAveCharWidth = aMetrics->aveCharWidth;
    }
    // Apparently hinting can mean that max_advance is not always accurate.
    aMetrics->maxAdvance =
        std::max(aMetrics->maxAdvance, aMetrics->aveCharWidth);

    // gfxFont::Metrics::underlineOffset is the position of the top of the
    // underline.
    //
    // FT_FaceRec documentation describes underline_position as "the
    // center of the underlining stem".  This was the original definition
    // of the PostScript metric, but in the PostScript table of OpenType
    // fonts the metric is "the top of the underline"
    // (http://www.microsoft.com/typography/otspec/post.htm), and FreeType
    // (up to version 2.3.7) doesn't make any adjustment.
    //
    // Therefore get the underline position directly from the table
    // ourselves when this table exists.  Use FreeType's metrics for
    // other (including older PostScript) fonts.
    if (mFace->underline_position && mFace->underline_thickness && yScale > 0.0) {
        aMetrics->underlineSize = mFace->underline_thickness * yScale;
        TT_Postscript *post = static_cast<TT_Postscript*>
            (FT_Get_Sfnt_Table(mFace, ft_sfnt_post));
        if (post && post->underlinePosition) {
            aMetrics->underlineOffset = post->underlinePosition * yScale;
        } else {
            aMetrics->underlineOffset = mFace->underline_position * yScale
                + 0.5 * aMetrics->underlineSize;
        }
    } else { // No underline info.
        // Imitate Pango.
        aMetrics->underlineSize = emHeight / 14.0;
        aMetrics->underlineOffset = -aMetrics->underlineSize;
    }

    if (os2 && os2->yStrikeoutSize && os2->yStrikeoutPosition && yScale > 0.0) {
        aMetrics->strikeoutSize = os2->yStrikeoutSize * yScale;
        aMetrics->strikeoutOffset = os2->yStrikeoutPosition * yScale;
    } else { // No strikeout info.
        aMetrics->strikeoutSize = aMetrics->underlineSize;
        // Use OpenType spec's suggested position for Roman font.
        aMetrics->strikeoutOffset = emHeight * 409.0 / 2048.0
            + 0.5 * aMetrics->strikeoutSize;
    }
    SnapLineToPixels(aMetrics->strikeoutOffset, aMetrics->strikeoutSize);

    if (os2 && os2->ySuperscriptYOffset) {
        gfxFloat val = ScaleRoundDesignUnits(os2->ySuperscriptYOffset,
                                             ftMetrics.y_scale);
        aMetrics->superscriptOffset = std::max(1.0, val);
    } else {
        aMetrics->superscriptOffset = aMetrics->xHeight;
    }
    
    if (os2 && os2->ySubscriptYOffset) {
        gfxFloat val = ScaleRoundDesignUnits(os2->ySubscriptYOffset,
                                             ftMetrics.y_scale);
        // some fonts have the incorrect sign. 
        val = fabs(val);
        aMetrics->subscriptOffset = std::max(1.0, val);
    } else {
        aMetrics->subscriptOffset = aMetrics->xHeight;
    }

    aMetrics->maxHeight = aMetrics->maxAscent + aMetrics->maxDescent;

    // Make the line height an integer number of pixels so that lines will be
    // equally spaced (rather than just being snapped to pixels, some up and
    // some down).  Layout calculates line height from the emHeight +
    // internalLeading + externalLeading, but first each of these is rounded
    // to layout units.  To ensure that the result is an integer number of
    // pixels, round each of the components to pixels.
    aMetrics->emHeight = floor(emHeight + 0.5);

    // maxHeight will normally be an integer, but round anyway in case
    // FreeType is configured differently.
    aMetrics->internalLeading =
        floor(aMetrics->maxHeight - aMetrics->emHeight + 0.5);

    // Text input boxes currently don't work well with lineHeight
    // significantly less than maxHeight (with Verdana, for example).
    lineHeight = floor(std::max(lineHeight, aMetrics->maxHeight) + 0.5);
    aMetrics->externalLeading =
        lineHeight - aMetrics->internalLeading - aMetrics->emHeight;

    // Ensure emAscent + emDescent == emHeight
    gfxFloat sum = aMetrics->emAscent + aMetrics->emDescent;
    aMetrics->emAscent = sum > 0.0 ?
        aMetrics->emAscent * aMetrics->emHeight / sum : 0.0;
    aMetrics->emDescent = aMetrics->emHeight - aMetrics->emAscent;
}

uint32_t
gfxFT2LockedFace::GetGlyph(uint32_t aCharCode)
{
    if (MOZ_UNLIKELY(!mFace))
        return 0;

#ifdef HAVE_FONTCONFIG_FCFREETYPE_H
    // FcFreeTypeCharIndex will search starting from the most recently
    // selected charmap.  This can cause non-determistic behavior when more
    // than one charmap supports a character but with different glyphs, as
    // with older versions of MS Gothic, for example.  Always prefer a Unicode
    // charmap, if there is one.  (FcFreeTypeCharIndex usually does the
    // appropriate Unicode conversion, but some fonts have non-Roman glyphs
    // for FT_ENCODING_APPLE_ROMAN characters.)
    if (!mFace->charmap || mFace->charmap->encoding != FT_ENCODING_UNICODE) {
        FT_Select_Charmap(mFace, FT_ENCODING_UNICODE);
    }

    return FcFreeTypeCharIndex(mFace, aCharCode);
#else
    return FT_Get_Char_Index(mFace, aCharCode);
#endif
}

typedef FT_UInt (*GetCharVariantFunction)(FT_Face  face,
                                          FT_ULong charcode,
                                          FT_ULong variantSelector);

uint32_t
gfxFT2LockedFace::GetUVSGlyph(uint32_t aCharCode, uint32_t aVariantSelector)
{
    NS_PRECONDITION(aVariantSelector, "aVariantSelector should not be NULL");

    if (MOZ_UNLIKELY(!mFace))
        return 0;

    // This function is available from FreeType 2.3.6 (June 2008).
    static CharVariantFunction sGetCharVariantPtr = FindCharVariantFunction();
    if (!sGetCharVariantPtr)
        return 0;

#ifdef HAVE_FONTCONFIG_FCFREETYPE_H
    // FcFreeTypeCharIndex may have changed the selected charmap.
    // FT_Face_GetCharVariantIndex needs a unicode charmap.
    if (!mFace->charmap || mFace->charmap->encoding != FT_ENCODING_UNICODE) {
        FT_Select_Charmap(mFace, FT_ENCODING_UNICODE);
    }
#endif

    return (*sGetCharVariantPtr)(mFace, aCharCode, aVariantSelector);
}

uint32_t
gfxFT2LockedFace::GetCharExtents(char aChar, cairo_text_extents_t* aExtents)
{
    NS_PRECONDITION(aExtents != nullptr, "aExtents must not be NULL");

    if (!mFace)
        return 0;

    FT_UInt gid = mGfxFont->GetGlyph(aChar);
    if (gid) {
        mGfxFont->GetGlyphExtents(gid, aExtents);
    }

    return gid;
}

gfxFT2LockedFace::CharVariantFunction
gfxFT2LockedFace::FindCharVariantFunction()
{
    // This function is available from FreeType 2.3.6 (June 2008).
    PRLibrary *lib = nullptr;
    CharVariantFunction function =
        reinterpret_cast<CharVariantFunction>
        (PR_FindFunctionSymbolAndLibrary("FT_Face_GetCharVariantIndex", &lib));
    if (!lib) {
        return nullptr;
    }

    FT_Int major;
    FT_Int minor;
    FT_Int patch;
    FT_Library_Version(mFace->glyph->library, &major, &minor, &patch);

    // Versions 2.4.0 to 2.4.3 crash if configured with
    // FT_CONFIG_OPTION_OLD_INTERNALS.  Presence of the symbol FT_Alloc
    // indicates FT_CONFIG_OPTION_OLD_INTERNALS.
    if (major == 2 && minor == 4 && patch < 4 &&
        PR_FindFunctionSymbol(lib, "FT_Alloc")) {
        function = nullptr;
    }

    // Decrement the reference count incremented in
    // PR_FindFunctionSymbolAndLibrary.
    PR_UnloadLibrary(lib);

    return function;
}