Make subpixel antialiasing of text work on Mac OS X under carbon

Implement the alphaRGBMapForGlyph function and make use of it in
the raster engine. The gamma correction is currently hardcoded to 2.0
which looks very good on two separate displays (iMac and MacBook Pro).
Ideally this would be picked from the system settings or computed
dynamically, but as long as 2.0 works, we'll stick to that.

Reviewed-by: Samuel

2 files changed, 77 insertions, 36 deletions

diff --git a/src/gui/text/qfontengine_mac.mm b/src/gui/text/qfontengine_mac.mm
index 425cab2..6b5bd0f 100644
--- a/src/gui/text/qfontengine_mac.mm
+++ b/src/gui/text/qfontengine_mac.mm
@@ -135,12 +135,12 @@ QCoreTextFontEngineMulti::QCoreTextFontEngineMulti(const ATSFontFamilyRef &, con
         symbolicTraits |= kCTFontItalicTrait;
         break;
     }
-    
+
     QCFString name;
     ATSFontGetName(atsFontRef, kATSOptionFlagsDefault, &name);
-    QCFType<CTFontDescriptorRef> descriptor = CTFontDescriptorCreateWithNameAndSize(name, fontDef.pixelSize);
-    QCFType<CTFontRef> baseFont = CTFontCreateWithFontDescriptor(descriptor, fontDef.pixelSize, 0); 
-    ctfont = CTFontCreateCopyWithSymbolicTraits(baseFont, fontDef.pixelSize, 0, symbolicTraits, symbolicTraits);
+    QCFType<CTFontDescriptorRef> descriptor = CTFontDescriptorCreateWithNameAndSize(name, fontDef.pointSize);
+    QCFType<CTFontRef> baseFont = CTFontCreateWithFontDescriptor(descriptor, fontDef.pointSize, 0);
+    ctfont = CTFontCreateCopyWithSymbolicTraits(baseFont, fontDef.pointSize, 0, symbolicTraits, symbolicTraits);
 
     // CTFontCreateCopyWithSymbolicTraits returns NULL if we ask for a trait that does
     // not exist for the given font. (for example italic)
@@ -162,7 +162,7 @@ QCoreTextFontEngineMulti::QCoreTextFontEngineMulti(const ATSFontFamilyRef &, con
     QCoreTextFontEngine *fe = new QCoreTextFontEngine(ctfont, fontDef, this);
     fe->ref.ref();
     engines.append(fe);
-    
+
 }
 
 QCoreTextFontEngineMulti::~QCoreTextFontEngineMulti()
@@ -176,7 +176,7 @@ uint QCoreTextFontEngineMulti::fontIndexForFont(CTFontRef id) const
         if (CFEqual(engineAt(i)->ctfont, id))
             return i;
     }
-    
+
     QCoreTextFontEngineMulti *that = const_cast<QCoreTextFontEngineMulti *>(this);
     QCoreTextFontEngine *fe = new QCoreTextFontEngine(id, fontDef, that);
     fe->ref.ref();
@@ -227,7 +227,7 @@ bool QCoreTextFontEngineMulti::stringToCMap(const QChar *str, int len, QGlyphLay
             CTFontRef runFont = static_cast<CTFontRef>(CFDictionaryGetValue(runAttribs, NSFontAttributeName));
             const uint fontIndex = (fontIndexForFont(runFont) << 24);
             //NSLog(@"Run Font Name = %@", CTFontCopyFamilyName(runFont));
-            QVarLengthArray<CGGlyph, 512> cgglyphs(0);           
+            QVarLengthArray<CGGlyph, 512> cgglyphs(0);
             const CGGlyph *tmpGlyphs = CTRunGetGlyphsPtr(run);
             if (!tmpGlyphs) {
                 cgglyphs.resize(glyphCount);
@@ -260,7 +260,7 @@ bool QCoreTextFontEngineMulti::stringToCMap(const QChar *str, int len, QGlyphLay
 
                 CFIndex k = 0;
                 CFIndex i = 0;
-                for (i = stringRange.location; 
+                for (i = stringRange.location;
                      (i < stringRange.location + stringRange.length) && (k < glyphCount); ++i) {
                     if (tmpIndices[k * rtlSign + rtlOffset] == i || i == stringRange.location) {
                         logClusters[i] = k + firstGlyphIndex;
@@ -425,28 +425,28 @@ void QCoreTextFontEngine::draw(CGContextRef ctx, qreal x, qreal y, const QTextIt
     getGlyphPositions(ti.glyphs, matrix, ti.flags, glyphs, positions);
     if (glyphs.size() == 0)
         return;
-    
+
     CGContextSetFontSize(ctx, fontDef.pixelSize);
-    
+
     CGAffineTransform oldTextMatrix = CGContextGetTextMatrix(ctx);
-    
+
     CGAffineTransform cgMatrix = CGAffineTransformMake(1, 0, 0, -1, 0, -paintDeviceHeight);
-    
+
     CGAffineTransformConcat(cgMatrix, oldTextMatrix);
-    
+
     if (synthesisFlags & QFontEngine::SynthesizedItalic)
         cgMatrix = CGAffineTransformConcat(cgMatrix, CGAffineTransformMake(1, 0, -tanf(14 * acosf(0) / 90), 1, 0, 0));
-    
+
 // ###    cgMatrix = CGAffineTransformConcat(cgMatrix, transform);
-    
+
     CGContextSetTextMatrix(ctx, cgMatrix);
-    
+
     CGContextSetTextDrawingMode(ctx, kCGTextFill);
-    
-    
+
+
     QVarLengthArray<CGSize> advances(glyphs.size());
     QVarLengthArray<CGGlyph> cgGlyphs(glyphs.size());
-    
+
     for (int i = 0; i < glyphs.size() - 1; ++i) {
         advances[i].width = (positions[i + 1].x - positions[i].x).toReal();
         advances[i].height = (positions[i + 1].y - positions[i].y).toReal();
@@ -455,21 +455,21 @@ void QCoreTextFontEngine::draw(CGContextRef ctx, qreal x, qreal y, const QTextIt
     advances[glyphs.size() - 1].width = 0;
     advances[glyphs.size() - 1].height = 0;
     cgGlyphs[glyphs.size() - 1] = glyphs[glyphs.size() - 1];
-    
+
     CGContextSetFont(ctx, cgFont);
     //NSLog(@"Font inDraw %@  ctfont %@", CGFontCopyFullName(cgFont), CTFontCopyFamilyName(ctfont));
-    
+
     CGContextSetTextPosition(ctx, positions[0].x.toReal(), positions[0].y.toReal());
-    
+
     CGContextShowGlyphsWithAdvances(ctx, cgGlyphs.data(), advances.data(), glyphs.size());
-    
+
     if (synthesisFlags & QFontEngine::SynthesizedBold) {
         CGContextSetTextPosition(ctx, positions[0].x.toReal() + 0.5 * lineThickness().toReal(),
                                  positions[0].y.toReal());
-        
+
         CGContextShowGlyphsWithAdvances(ctx, cgGlyphs.data(), advances.data(), glyphs.size());
     }
-    
+
     CGContextSetTextMatrix(ctx, oldTextMatrix);
 }
 
@@ -622,7 +622,7 @@ QFontEngine::FaceId QCoreTextFontEngine::faceId() const
 
 bool QCoreTextFontEngine::canRender(const QChar *string, int len)
 {
-    QCFType<CTFontRef> retFont = CTFontCreateForString(ctfont, 
+    QCFType<CTFontRef> retFont = CTFontCreateForString(ctfont,
                   QCFType<CFStringRef>(CFStringCreateWithCharactersNoCopy(0,
                                                               reinterpret_cast<const UniChar *>(string),
                                                                           len, kCFAllocatorNull)),
@@ -672,7 +672,7 @@ QFontEngineMacMulti::QFontEngineMacMulti(const ATSFontFamilyRef &atsFamily, cons
     } else {
         if (fontDef.weight >= QFont::Bold)
             fntStyle |= ::bold;
-        if (fontDef.style != QFont::StyleNormal) 
+        if (fontDef.style != QFont::StyleNormal)
             fntStyle |= ::italic;
 
         FMFontStyle intrinsicStyle;
@@ -955,7 +955,7 @@ bool QFontEngineMacMulti::stringToCMap(const QChar *str, int len, QGlyphLayout *
         tmpItem.length = charCount;
         tmpItem.glyphs = shaperItem.glyphs.mid(glyphIdx, glyphCount);
         tmpItem.log_clusters = shaperItem.log_clusters + charIdx;
-        if (!stringToCMapInternal(tmpItem.string + tmpItem.from, tmpItem.length, 
+        if (!stringToCMapInternal(tmpItem.string + tmpItem.from, tmpItem.length,
                                   &tmpItem.glyphs, &glyphCount, flags,
                                   &tmpItem)) {
             *nglyphs = glyphIdx + glyphCount;
@@ -1221,12 +1221,12 @@ QFontEngineMac::QFontEngineMac(ATSUStyle baseStyle, ATSUFontID fontID, const QFo
 	transform = multiEngine->transform;
     else
 	transform = CGAffineTransformIdentity;
-    
+
     ATSUTextMeasurement metric;
 
     ATSUGetAttribute(style, kATSUAscentTag, sizeof(metric), &metric, 0);
     m_ascent = FixRound(metric);
-   
+
     ATSUGetAttribute(style, kATSUDescentTag, sizeof(metric), &metric, 0);
     m_descent = FixRound(metric);
 
@@ -1422,11 +1422,16 @@ void QFontEngineMac::addGlyphsToPath(glyph_t *glyphs, QFixedPoint *positions, in
     addGlyphsToPathHelper(style, glyphs, positions, numGlyphs, path);
 }
 
-QImage QFontEngineMac::alphaMapForGlyph(glyph_t glyph)
+
+/*!
+  Helper function for alphaMapForGlyph and alphaRGBMapForGlyph. The two are identical, except for
+  the subpixel antialiasing...
+*/
+QImage QFontEngineMac::imageForGlyph(glyph_t glyph, int margin, bool colorful)
 {
     const glyph_metrics_t br = boundingBox(glyph);
     QImage im(qRound(br.width)+2, qRound(br.height)+4, QImage::Format_RGB32);
-    im.fill(0);
+    im.fill(0xff000000);
 
     CGColorSpaceRef colorspace = QCoreGraphicsPaintEngine::macGenericColorSpace();
 #if (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4)
@@ -1444,7 +1449,7 @@ QImage QFontEngineMac::alphaMapForGlyph(glyph_t glyph)
     CGContextSetFontSize(ctx, fontDef.pixelSize);
     CGContextSetShouldAntialias(ctx, fontDef.pointSize > qt_antialiasing_threshold && !(fontDef.styleStrategy & QFont::NoAntialias));
     // turn off sub-pixel hinting - no support for that in OpenGL
-    CGContextSetShouldSmoothFonts(ctx, false);
+    CGContextSetShouldSmoothFonts(ctx, colorful);
     CGAffineTransform oldTextMatrix = CGContextGetTextMatrix(ctx);
     CGAffineTransform cgMatrix = CGAffineTransformMake(1, 0, 0, 1, 0, 0);
     CGAffineTransformConcat(cgMatrix, oldTextMatrix);
@@ -1476,6 +1481,13 @@ QImage QFontEngineMac::alphaMapForGlyph(glyph_t glyph)
 
     CGContextRelease(ctx);
 
+    return im;
+}
+
+QImage QFontEngineMac::alphaMapForGlyph(glyph_t glyph)
+{
+    QImage im = imageForGlyph(glyph, 2, false);
+
     QImage indexed(im.width(), im.height(), QImage::Format_Indexed8);
     QVector<QRgb> colors(256);
     for (int i=0; i<256; ++i)
@@ -1495,6 +1507,32 @@ QImage QFontEngineMac::alphaMapForGlyph(glyph_t glyph)
     return indexed;
 }
 
+QImage QFontEngineMac::alphaRGBMapForGlyph(glyph_t glyph, int margin, const QTransform &t)
+{
+    QImage im = imageForGlyph(glyph, margin, true);
+
+    if (t.type() >= QTransform::TxScale) {
+        im = im.transformed(t);
+    }
+
+    extern uchar qt_pow_rgb_gamma[256];
+
+    // gamma correct the pixels back to linear color space...
+    for (int y=0; y<im.height(); ++y) {
+        uint *pixels = (uint *) im.scanLine(y);
+        for (int x=0; x<im.width(); ++x) {
+            uint p = pixels[x];
+            uint r = qt_pow_rgb_gamma[qRed(p)];
+            uint g = qt_pow_rgb_gamma[qGreen(p)];
+            uint b = qt_pow_rgb_gamma[qBlue(p)];
+            pixels[x] = (r << 16) | (g << 8) | b | 0xff000000;
+        }
+    }
+
+    return im;
+}
+
+
 bool QFontEngineMac::canRender(const QChar *string, int len)
 {
     Q_ASSERT(false);
@@ -1648,7 +1686,7 @@ QFontEngine::Properties QFontEngineMac::properties() const
     if (ATSFontGetTable(atsFont, MAKE_TAG('p', 'o', 's', 't'), 10, 2, &lw, 0) == noErr)
        lw = qFromBigEndian<quint16>(lw);
     props.lineWidth = lw;
-    
+
     // CTFontCopyPostScriptName
     QCFString psName;
     if (ATSFontGetPostScriptName(FMGetATSFontRefFromFont(fontID), kATSOptionFlagsDefault, &psName) == noErr)
@@ -1663,7 +1701,7 @@ void QFontEngineMac::getUnscaledGlyph(glyph_t glyph, QPainterPath *path, glyph_m
     ATSUCreateAndCopyStyle(style, &unscaledStyle);
 
     int emSquare = properties().emSquare.toInt();
-    
+
     const int maxAttributeCount = 4;
     ATSUAttributeTag tags[maxAttributeCount + 1];
     ByteCount sizes[maxAttributeCount + 1];
@@ -1675,7 +1713,7 @@ void QFontEngineMac::getUnscaledGlyph(glyph_t glyph, QPainterPath *path, glyph_m
     sizes[attributeCount] = sizeof(size);
     values[attributeCount] = &size;
     ++attributeCount;
-    
+
     Q_ASSERT(attributeCount < maxAttributeCount + 1);
     OSStatus err = ATSUSetAttributes(unscaledStyle, attributeCount, tags, sizes, values);
     Q_ASSERT(err == noErr);
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 176c728..8f6b92a 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -525,8 +525,11 @@ public:
     virtual Properties properties() const;
     virtual void getUnscaledGlyph(glyph_t glyph, QPainterPath *path, glyph_metrics_t *metrics);
     virtual QImage alphaMapForGlyph(glyph_t);
+    virtual QImage alphaRGBMapForGlyph(glyph_t, int margin, const QTransform &t);
 
 private:
+    QImage imageForGlyph(glyph_t glyph, int margin, bool colorful);
+
     ATSUFontID fontID;
     QCFType<CGFontRef> cgFont;
     ATSUStyle style;