зеркало из https://github.com/mozilla/moz-skia.git
implement gamma correction for freetype text.
Need to opt-in to have it applied to kA8 text (which chrome can't for a while) A8 text needs to use Slight hinting to look better, but that is not forced... git-svn-id: http://skia.googlecode.com/svn/trunk@3277 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
reed@google.com
Родитель
cef7e3fc4b
Коммит
1ac8350821
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@ -78,6 +78,8 @@
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'defines': [
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'SK_SAMPLES_FOR_X',
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'SK_BUILD_FOR_UNIX',
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'SK_USE_COLOR_LUMINANCE',
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'SK_GAMMA_APPLY_TO_A8',
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],
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'configurations': {
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'Debug': {
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@ -54,6 +54,10 @@
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//#define ENABLE_GLYPH_SPEW // for tracing calls
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//#define DUMP_STRIKE_CREATION
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//#define SK_GAMMA_APPLY_TO_A8
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#define SK_GAMMA_CONTRAST 0x33
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#define SK_GAMMA_EXPONENT 1.8
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#ifdef SK_DEBUG
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#define SkASSERT_CONTINUE(pred) \
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do { \
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@ -66,14 +70,6 @@
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using namespace skia_advanced_typeface_metrics_utils;
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// SK_FREETYPE_LCD_LERP should be 0...256
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// 0 means no color reduction (e.g. just as returned from FreeType)
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// 256 means 100% color reduction (e.g. gray)
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//
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#ifndef SK_FREETYPE_LCD_LERP
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#define SK_FREETYPE_LCD_LERP 96
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#endif
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static bool isLCD(const SkScalerContext::Rec& rec) {
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switch (rec.fMaskFormat) {
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case SkMask::kLCD16_Format:
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@ -113,7 +109,8 @@ InitFreetype() {
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// Setup LCD filtering. This reduces colour fringes for LCD rendered
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// glyphs.
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#ifdef FT_LCD_FILTER_H
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err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_DEFAULT);
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// err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_DEFAULT);
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err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_LIGHT);
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gLCDSupport = err == 0;
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#else
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gLCDSupport = false;
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@ -630,11 +627,13 @@ void SkFontHost::FilterRec(SkScalerContext::Rec* rec) {
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if (SkPaint::kFull_Hinting == h && !isLCD(*rec)) {
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// collapse full->normal hinting if we're not doing LCD
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h = SkPaint::kNormal_Hinting;
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} else if ((rec->fFlags & SkScalerContext::kSubpixelPositioning_Flag) &&
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SkPaint::kNo_Hinting != h) {
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// to do subpixel, we must have at most slight hinting
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h = SkPaint::kSlight_Hinting;
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}
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if ((rec->fFlags & SkScalerContext::kSubpixelPositioning_Flag) || isLCD(*rec)) {
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if (SkPaint::kNo_Hinting != h) {
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h = SkPaint::kSlight_Hinting;
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}
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}
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#ifndef SK_IGNORE_ROTATED_FREETYPE_FIX
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// rotated text looks bad with hinting, so we disable it as needed
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if (!isAxisAligned(*rec)) {
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@ -643,6 +642,7 @@ void SkFontHost::FilterRec(SkScalerContext::Rec* rec) {
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#endif
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rec->setHinting(h);
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#ifndef SK_USE_COLOR_LUMINANCE
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// for compatibility at the moment, discretize luminance to 3 settings
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// black, white, gray. This helps with fontcache utilization, since we
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// won't create multiple entries that in the end map to the same results.
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@ -662,6 +662,7 @@ void SkFontHost::FilterRec(SkScalerContext::Rec* rec) {
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}
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rec->setLuminanceBits(lum);
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}
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#endif
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}
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#ifdef SK_BUILD_FOR_ANDROID
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@ -1038,19 +1039,71 @@ void SkScalerContext_FreeType::generateMetrics(SkGlyph* glyph) {
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#endif
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}
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static int lerp(int start, int end) {
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SkASSERT((unsigned)SK_FREETYPE_LCD_LERP <= 256);
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return start + ((end - start) * (SK_FREETYPE_LCD_LERP) >> 8);
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///////////////////////////////////////////////////////////////////////////////
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static int apply_contrast(int srca, int contrast) {
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return srca + (((255 - srca) * contrast * srca) / (255*255));
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}
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static uint16_t packTriple(unsigned r, unsigned g, unsigned b) {
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if (SK_FREETYPE_LCD_LERP) {
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// want (a+b+c)/3, but we approx to avoid the divide
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unsigned ave = (5 * (r + g + b) + b) >> 4;
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r = lerp(r, ave);
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g = lerp(g, ave);
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b = lerp(b, ave);
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static void build_power_table(uint8_t table[], float ee) {
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for (int i = 0; i < 256; i++) {
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float x = i / 255.f;
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x = powf(x, ee);
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int xx = SkScalarRoundToInt(SkFloatToScalar(x * 255));
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table[i] = SkToU8(xx);
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}
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}
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static void build_gamma_table(uint8_t table[256], int src, int dst) {
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static bool gInit;
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static uint8_t powTable[256], invPowTable[256];
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if (!gInit) {
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const float g = SK_GAMMA_EXPONENT;
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build_power_table(powTable, g);
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build_power_table(invPowTable, 1/g);
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gInit = true;
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}
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int linSrc = powTable[src];
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int linDst = powTable[dst];
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for (int i = 0; i < 256; ++i) {
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int srca = i;
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int dsta = 255 - srca;
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//Calculate the output we want.
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int linOut = (linSrc * srca + dsta * linDst) / 255;
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SkASSERT((unsigned)linOut <= 255);
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int out = invPowTable[linOut];
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//Undo what the blit blend will do.
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int result = ((255 * out) - (255 * dst)) / (src - dst);
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SkASSERT((unsigned)result <= 255);
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result = apply_contrast(result, SK_GAMMA_CONTRAST);
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SkASSERT((unsigned)result <= 255);
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table[srca] = result;
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}
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}
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static const uint8_t* getGammaTable(U8CPU luminance) {
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static uint8_t gGammaTables[4][256];
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static bool gInited;
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if (!gInited) {
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build_gamma_table(gGammaTables[0], 0x00, 0xFF);
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build_gamma_table(gGammaTables[1], 0x55, 0xAA);
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build_gamma_table(gGammaTables[2], 0xAA, 0x55);
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build_gamma_table(gGammaTables[3], 0xFF, 0x00);
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gInited = true;
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}
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SkASSERT(0 == (luminance >> 8));
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return gGammaTables[luminance >> 6];
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}
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static uint16_t packTriple(unsigned r, unsigned g, unsigned b) {
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return SkPackRGB16(r >> 3, g >> 2, b >> 3);
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}
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@ -1066,7 +1119,8 @@ static int bittst(const uint8_t data[], int bitOffset) {
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}
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static void copyFT2LCD16(const SkGlyph& glyph, const FT_Bitmap& bitmap,
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int lcdIsBGR) {
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int lcdIsBGR, const uint8_t* tableR,
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const uint8_t* tableG, const uint8_t* tableB) {
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SkASSERT(glyph.fHeight == bitmap.rows);
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uint16_t* dst = reinterpret_cast<uint16_t*>(glyph.fImage);
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const size_t dstRB = glyph.rowBytes();
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@ -1099,12 +1153,16 @@ static void copyFT2LCD16(const SkGlyph& glyph, const FT_Bitmap& bitmap,
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const uint8_t* triple = src;
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if (lcdIsBGR) {
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for (int x = 0; x < width; x++) {
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dst[x] = packTriple(triple[2], triple[1], triple[0]);
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dst[x] = packTriple(tableR[triple[2]],
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tableG[triple[1]],
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tableB[triple[0]]);
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triple += 3;
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}
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} else {
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for (int x = 0; x < width; x++) {
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dst[x] = packTriple(triple[0], triple[1], triple[2]);
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dst[x] = packTriple(tableR[triple[0]],
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tableG[triple[1]],
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tableB[triple[2]]);
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triple += 3;
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}
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}
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@ -1133,6 +1191,18 @@ void SkScalerContext_FreeType::generateImage(const SkGlyph& glyph) {
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return;
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}
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#ifdef SK_USE_COLOR_LUMINANCE
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SkColor lumColor = fRec.getLuminanceColor();
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const uint8_t* tableR = getGammaTable(SkColorGetR(lumColor));
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const uint8_t* tableG = getGammaTable(SkColorGetG(lumColor));
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const uint8_t* tableB = getGammaTable(SkColorGetB(lumColor));
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#else
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unsigned lum = fRec.getLuminanceByte();
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const uint8_t* tableR = getGammaTable(lum);
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const uint8_t* tableG = getGammaTable(lum);
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const uint8_t* tableB = getGammaTable(lum);
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#endif
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switch ( fFace->glyph->format ) {
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case FT_GLYPH_FORMAT_OUTLINE: {
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FT_Outline* outline = &fFace->glyph->outline;
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@ -1165,7 +1235,8 @@ void SkScalerContext_FreeType::generateImage(const SkGlyph& glyph) {
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if (SkMask::kLCD16_Format == glyph.fMaskFormat) {
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FT_Render_Glyph(fFace->glyph, FT_RENDER_MODE_LCD);
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copyFT2LCD16(glyph, fFace->glyph->bitmap,
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fRec.fFlags & SkScalerContext::kLCD_BGROrder_Flag);
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fRec.fFlags & SkScalerContext::kLCD_BGROrder_Flag,
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tableR, tableG, tableB);
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} else {
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target.width = glyph.fWidth;
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target.rows = glyph.fHeight;
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@ -1231,7 +1302,8 @@ void SkScalerContext_FreeType::generateImage(const SkGlyph& glyph) {
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}
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} else if (SkMask::kLCD16_Format == glyph.fMaskFormat) {
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copyFT2LCD16(glyph, fFace->glyph->bitmap,
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fRec.fFlags & SkScalerContext::kLCD_BGROrder_Flag);
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fRec.fFlags & SkScalerContext::kLCD_BGROrder_Flag,
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tableR, tableG, tableB);
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} else {
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SkDEBUGFAIL("unknown glyph bitmap transform needed");
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}
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@ -1242,25 +1314,21 @@ void SkScalerContext_FreeType::generateImage(const SkGlyph& glyph) {
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goto ERROR;
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}
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if (gGammaTables[0] || gGammaTables[1]) {
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bool isWhite = fRec.getLuminanceByte() >= WHITE_LUMINANCE_LIMIT;
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bool isBlack = fRec.getLuminanceByte() <= BLACK_LUMINANCE_LIMIT;
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if ((isWhite | isBlack) && SkMask::kA8_Format == glyph.fMaskFormat) {
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int index = isBlack ? 0 : 1;
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if (gGammaTables[index]) {
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const uint8_t* SK_RESTRICT table = gGammaTables[index];
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uint8_t* SK_RESTRICT dst = (uint8_t*)glyph.fImage;
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unsigned rowBytes = glyph.rowBytes();
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for (int y = glyph.fHeight - 1; y >= 0; --y) {
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for (int x = glyph.fWidth - 1; x >= 0; --x) {
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dst[x] = table[dst[x]];
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}
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dst += rowBytes;
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}
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#ifdef SK_GAMMA_APPLY_TO_A8
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if (SkMask::kA8_Format == glyph.fMaskFormat) {
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SkASSERT(tableR == tableG && tableR == tableB);
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const uint8_t* table = tableR;
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uint8_t* SK_RESTRICT dst = (uint8_t*)glyph.fImage;
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unsigned rowBytes = glyph.rowBytes();
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for (int y = glyph.fHeight - 1; y >= 0; --y) {
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for (int x = glyph.fWidth - 1; x >= 0; --x) {
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dst[x] = table[dst[x]];
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}
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dst += rowBytes;
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}
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}
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#endif
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}
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///////////////////////////////////////////////////////////////////////////////
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