Handle transparent pen color in fast text path

Switches the text blending to be SourceOver as that is
much more common than Source, and means we can now handle
semi-transparent text colors there.

Task-number: QTBUG-72165
Change-Id: I7b3aedb22412e6fb6f60197596b37f26c6008784
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

4 files changed, 101 insertions, 94 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index edb363ac69..3d06a27d8e 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -5658,44 +5658,60 @@ static inline void alphamapblend_argb32(quint32 *dst, int coverage, QRgba64 srcL
 {
     if (coverage == 0) {
         // nothing
-    } else if (coverage == 255) {
-        *dst = src;
-    } else if (!colorProfile) {
-        *dst = INTERPOLATE_PIXEL_255(src, coverage, *dst, 255 - coverage);
+    } else if (coverage == 255 || !colorProfile) {
+        blend_pixel(*dst, src, coverage);
+    } else if (*dst < 0xff000000) {
+        // Give up and do a naive gray alphablend. Needed to deal with ARGB32 and invalid ARGB32_premultiplied, see QTBUG-60571
+        blend_pixel(*dst, src, coverage);
+    } else if (src >= 0xff000000) {
+        grayBlendPixel(dst, coverage, srcLinear, colorProfile);
     } else {
-        if (*dst >= 0xff000000) {
-            grayBlendPixel(dst, coverage, srcLinear, colorProfile);
-        } else {
-            // Give up and do a naive gray alphablend. Needed to deal with ARGB32 and invalid ARGB32_premultiplied, see QTBUG-60571
-            *dst = INTERPOLATE_PIXEL_255(src, coverage, *dst, 255 - coverage);
-        }
+        // First do naive blend with text-color
+        QRgb s = *dst;
+        blend_pixel(s, src);
+        // Then gamma-corrected blend with glyph shape
+        grayBlendPixel(dst, coverage, colorProfile->toLinear64(s), colorProfile);
     }
 }
 
 #if QT_CONFIG(raster_64bit)
+
+static inline void grayBlendPixel(QRgba64 &dst, int coverage, QRgba64 srcLinear, const QColorTrcLut *colorProfile)
+{
+    // Do a gammacorrected gray alphablend...
+    QRgba64 dstColor = dst;
+    if (colorProfile) {
+        if (dstColor.isOpaque())
+            dstColor = colorProfile->toLinear(dstColor);
+        else if (!dstColor.isTransparent())
+            dstColor = colorProfile->toLinear(dstColor.unpremultiplied()).premultiplied();
+    }
+
+    blend_pixel(dstColor, srcLinear, coverage);
+
+    if (colorProfile) {
+        if (dstColor.isOpaque())
+            dstColor = colorProfile->fromLinear(dstColor);
+        else if (!dstColor.isTransparent())
+            dstColor = colorProfile->fromLinear(dstColor.unpremultiplied()).premultiplied();
+    }
+    dst = dstColor;
+}
+
 static inline void alphamapblend_generic(int coverage, QRgba64 *dest, int x, const QRgba64 &srcLinear, const QRgba64 &src, const QColorTrcLut *colorProfile)
 {
     if (coverage == 0) {
         // nothing
     } else if (coverage == 255) {
-        dest[x] = src;
+        blend_pixel(dest[x], src);
+    } else if (src.isOpaque()) {
+        grayBlendPixel(dest[x], coverage, srcLinear, colorProfile);
     } else {
-        QRgba64 dstColor = dest[x];
-        if (colorProfile) {
-            if (dstColor.isOpaque())
-                dstColor = colorProfile->toLinear(dstColor);
-            else if (!dstColor.isTransparent())
-                dstColor = colorProfile->toLinear(dstColor.unpremultiplied()).premultiplied();
-        }
-
-        dstColor = interpolate255(srcLinear, coverage, dstColor, 255 - coverage);
-        if (colorProfile) {
-            if (dstColor.isOpaque())
-                dstColor = colorProfile->fromLinear(dstColor);
-            else if (!dstColor.isTransparent())
-                dstColor = colorProfile->fromLinear(dstColor.unpremultiplied()).premultiplied();
-        }
-        dest[x] = dstColor;
+        // First do naive blend with text-color
+        QRgba64 s = dest[x];
+        blend_pixel(s, src);
+        // Then gamma-corrected blend with glyph shape
+        grayBlendPixel(dest[x], coverage, colorProfile->toLinear(s), colorProfile);
     }
 }
 
@@ -5714,12 +5730,8 @@ static void qt_alphamapblit_generic(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA8Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     alignas(8) QRgba64 buffer[BufferSize];
     const DestFetchProc64 destFetch64 = destFetchProc64[rasterBuffer->format];
@@ -5792,12 +5804,8 @@ static void qt_alphamapblit_generic(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA8Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     quint32 buffer[BufferSize];
     const DestFetchProc destFetch = destFetchProc[rasterBuffer->format];
@@ -5872,7 +5880,7 @@ void qt_alphamapblit_quint16(QRasterBuffer *rasterBuffer,
                              int mapWidth, int mapHeight, int mapStride,
                              const QClipData *clip, bool useGammaCorrection)
 {
-    if (useGammaCorrection) {
+    if (useGammaCorrection || !color.isOpaque()) {
         qt_alphamapblit_generic(rasterBuffer, x, y, color, map, mapWidth, mapHeight, mapStride, clip, useGammaCorrection);
         return;
     }
@@ -5931,12 +5939,8 @@ static void qt_alphamapblit_argb32(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA8Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     if (!clip) {
         quint32 *dest = reinterpret_cast<quint32*>(rasterBuffer->scanLine(y)) + x;
@@ -6031,48 +6035,59 @@ static inline QRgb rgbBlend(QRgb d, QRgb s, uint rgbAlpha)
 #endif
 }
 
-#if QT_CONFIG(raster_64bit)
-static inline void alphargbblend_generic(uint coverage, QRgba64 *dest, int x, const QRgba64 &srcLinear, const QRgba64 &src, const QColorTrcLut *colorProfile)
+static inline void alphargbblend_argb32(quint32 *dst, uint coverage, const QRgba64 &srcLinear, quint32 src, const QColorTrcLut *colorProfile)
 {
     if (coverage == 0xff000000) {
         // nothing
-    } else if (coverage == 0xffffffff) {
-        dest[x] = src;
+    } else if (coverage == 0xffffffff && qAlpha(src) == 255) {
+        blend_pixel(*dst, src);
+    } else if (!colorProfile) {
+        *dst = rgbBlend(*dst, src, coverage);
+    } else if (*dst < 0xff000000) {
+        // Give up and do a naive gray alphablend. Needed to deal with ARGB32 and invalid ARGB32_premultiplied, see QTBUG-60571
+        blend_pixel(*dst, src, qRgbAvg(coverage));
+    } else if (srcLinear.isOpaque()) {
+        rgbBlendPixel(dst, coverage, srcLinear, colorProfile);
     } else {
-        QRgba64 dstColor = dest[x];
-        if (dstColor.isOpaque()) {
-            if (colorProfile)
-                dstColor = colorProfile->toLinear(dstColor);
-            dstColor = rgbBlend(dstColor, srcLinear, coverage);
-            if (colorProfile)
-                dstColor = colorProfile->fromLinear(dstColor);
-            dest[x] = dstColor;
-        } else {
-            // Do a gray alphablend.
-            alphamapblend_generic(qRgbAvg(coverage), dest, x, srcLinear, src, colorProfile);
-        }
+        // First do naive blend with text-color
+        QRgb s = *dst;
+        blend_pixel(s, src);
+        // Then gamma-corrected blend with glyph shape
+        rgbBlendPixel(dst, coverage, colorProfile->toLinear64(s), colorProfile);
     }
 }
-#endif
 
-static inline void alphargbblend_argb32(quint32 *dst, uint coverage, const QRgba64 &srcLinear, quint32 src, const QColorTrcLut *colorProfile)
+#if QT_CONFIG(raster_64bit)
+static inline void rgbBlendPixel(QRgba64 &dst, int coverage, QRgba64 slinear, const QColorTrcLut *colorProfile)
+{
+    // Do a gammacorrected RGB alphablend...
+    const QRgba64 dlinear = colorProfile ? colorProfile->toLinear64(dst) : dst;
+
+    QRgba64 blend = rgbBlend(dlinear, slinear, coverage);
+
+    dst = colorProfile ? colorProfile->fromLinear(blend) : blend;
+}
+
+static inline void alphargbblend_generic(uint coverage, QRgba64 *dest, int x, const QRgba64 &srcLinear, const QRgba64 &src, const QColorTrcLut *colorProfile)
 {
     if (coverage == 0xff000000) {
         // nothing
     } else if (coverage == 0xffffffff) {
-        *dst = src;
-    } else if (*dst < 0xff000000) {
-        // Give up and do a naive gray alphablend. Needed to deal with ARGB32 and invalid ARGB32_premultiplied, see QTBUG-60571
-        const int a = qRgbAvg(coverage);
-        *dst = INTERPOLATE_PIXEL_255(src, a, *dst, 255 - a);
-    } else if (!colorProfile) {
-        *dst = rgbBlend(*dst, src, coverage);
-    } else  {
-        rgbBlendPixel(dst, coverage, srcLinear, colorProfile);
+        blend_pixel(dest[x], src);
+    } else if (!dest[x].isOpaque()) {
+        // Do a gray alphablend.
+        alphamapblend_generic(qRgbAvg(coverage), dest, x, srcLinear, src, colorProfile);
+    } else if (src.isOpaque()) {
+        rgbBlendPixel(dest[x], coverage, srcLinear, colorProfile);
+    } else {
+        // First do naive blend with text-color
+        QRgba64 s = dest[x];
+        blend_pixel(s, src);
+        // Then gamma-corrected blend with glyph shape
+        rgbBlendPixel(dest[x], coverage, colorProfile->toLinear(s), colorProfile);
     }
 }
 
-#if QT_CONFIG(raster_64bit)
 static void qt_alphargbblit_generic(QRasterBuffer *rasterBuffer,
                                     int x, int y, const QRgba64 &color,
                                     const uint *src, int mapWidth, int mapHeight, int srcStride,
@@ -6087,12 +6102,8 @@ static void qt_alphargbblit_generic(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA32Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     alignas(8) QRgba64 buffer[BufferSize];
     const DestFetchProc64 destFetch64 = destFetchProc64[rasterBuffer->format];
@@ -6164,12 +6175,8 @@ static void qt_alphargbblit_generic(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA32Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     quint32 buffer[BufferSize];
     const DestFetchProc destFetch = destFetchProc[rasterBuffer->format];
@@ -6242,12 +6249,8 @@ static void qt_alphargbblit_argb32(QRasterBuffer *rasterBuffer,
         colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA32Text();
 
     QRgba64 srcColor = color;
-    if (colorProfile) {
-        if (color.isOpaque())
-            srcColor = colorProfile->toLinear(srcColor);
-        else
-            srcColor = colorProfile->toLinear(srcColor.unpremultiplied()).premultiplied();
-    }
+    if (colorProfile && color.isOpaque())
+        srcColor = colorProfile->toLinear(srcColor);
 
     if (!clip) {
         quint32 *dst = reinterpret_cast<quint32*>(rasterBuffer->scanLine(y)) + x;
diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h
index 9c5d525722..dd42b96d79 100644
--- a/src/gui/painting/qdrawhelper_p.h
+++ b/src/gui/painting/qdrawhelper_p.h
@@ -671,6 +671,8 @@ static Q_ALWAYS_INLINE void blend_pixel(quint32 &dst, const quint32 src)
 
 static Q_ALWAYS_INLINE void blend_pixel(quint32 &dst, const quint32 src, const int const_alpha)
 {
+    if (const_alpha == 255)
+        return blend_pixel(dst, src);
     if (src != 0) {
         const quint32 s = BYTE_MUL(src, const_alpha);
         dst = s + BYTE_MUL(dst, qAlpha(~s));
diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 9894da8fe1..447ecb358a 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -842,8 +842,8 @@ void QRasterPaintEngine::updateRasterState()
         const QPainter::CompositionMode mode = s->composition_mode;
         s->flags.fast_text = (s->penData.type == QSpanData::Solid)
                        && s->intOpacity == 256
-                       && (mode == QPainter::CompositionMode_Source
-                           || (mode == QPainter::CompositionMode_SourceOver
+                       && (mode == QPainter::CompositionMode_SourceOver
+                           || (mode == QPainter::CompositionMode_Source
                                && s->penData.solidColor.isOpaque()));
     }
 
diff --git a/src/gui/painting/qrgba64_p.h b/src/gui/painting/qrgba64_p.h
index ca879de27c..d145dbfbea 100644
--- a/src/gui/painting/qrgba64_p.h
+++ b/src/gui/painting/qrgba64_p.h
@@ -284,6 +284,8 @@ static Q_ALWAYS_INLINE void blend_pixel(QRgba64 &dst, QRgba64 src)
 
 static Q_ALWAYS_INLINE void blend_pixel(QRgba64 &dst, QRgba64 src, const int const_alpha)
 {
+    if (const_alpha == 255)
+        return blend_pixel(dst, src);
     if (!src.isTransparent()) {
         src = multiplyAlpha255(src, const_alpha);
         dst = src + multiplyAlpha65535(dst, 65535 - src.alpha());