QtGui: Avoid rgba64->rgba32 conversion on every pixel in gradient

Convert rgba64 color table to a new rgb32 color table only once. Use
this cache when required.

This patch can 2x speed up gradient painting using 32bit color format.

Task-number: QTBUG-50930
Change-Id: I9212e01e397c2e0127cdf3070cc49880a2d8df88
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>

3 files changed, 36 insertions, 15 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 28c7099d3c..f0e5810b54 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -3433,13 +3433,13 @@ static SourceFetchProc64 sourceFetch64[NBlendTypes][QImage::NImageFormats] = {
 static uint qt_gradient_pixel_fixed(const QGradientData *data, int fixed_pos)
 {
     int ipos = (fixed_pos + (FIXPT_SIZE / 2)) >> FIXPT_BITS;
-    return data->colorTable[qt_gradient_clamp(data, ipos)].toArgb32();
+    return data->colorTable32[qt_gradient_clamp(data, ipos)];
 }
 
 static const QRgba64& qt_gradient_pixel64_fixed(const QGradientData *data, int fixed_pos)
 {
     int ipos = (fixed_pos + (FIXPT_SIZE / 2)) >> FIXPT_BITS;
-    return data->colorTable[qt_gradient_clamp(data, ipos)];
+    return data->colorTable64[qt_gradient_clamp(data, ipos)];
 }
 
 static void QT_FASTCALL getLinearGradientValues(LinearGradientValues *v, const QSpanData *data)
diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h
index 1ff19f4e04..ff98d186c5 100644
--- a/src/gui/painting/qdrawhelper_p.h
+++ b/src/gui/painting/qdrawhelper_p.h
@@ -268,7 +268,8 @@ struct QGradientData
 #define GRADIENT_STOPTABLE_SIZE 1024
 #define GRADIENT_STOPTABLE_SIZE_SHIFT 10
 
-    QRgba64* colorTable; //[GRADIENT_STOPTABLE_SIZE];
+    const QRgba64 *colorTable64; //[GRADIENT_STOPTABLE_SIZE];
+    const QRgb *colorTable32; //[GRADIENT_STOPTABLE_SIZE];
 
     uint alphaColor : 1;
 };
@@ -376,13 +377,13 @@ static inline uint qt_gradient_clamp(const QGradientData *data, int ipos)
 static inline uint qt_gradient_pixel(const QGradientData *data, qreal pos)
 {
     int ipos = int(pos * (GRADIENT_STOPTABLE_SIZE - 1) + qreal(0.5));
-    return data->colorTable[qt_gradient_clamp(data, ipos)].toArgb32();
+    return data->colorTable32[qt_gradient_clamp(data, ipos)];
 }
 
 static inline const QRgba64& qt_gradient_pixel64(const QGradientData *data, qreal pos)
 {
     int ipos = int(pos * (GRADIENT_STOPTABLE_SIZE - 1) + qreal(0.5));
-    return data->colorTable[qt_gradient_clamp(data, ipos)];
+    return data->colorTable64[qt_gradient_clamp(data, ipos)];
 }
 
 static inline qreal qRadialDeterminant(qreal a, qreal b, qreal c)
@@ -550,7 +551,7 @@ public:
             delta_det4_vec.v = Simd::v_add(delta_det4_vec.v, v_delta_delta_det16); \
             b_vec.v = Simd::v_add(b_vec.v, v_delta_b4); \
             for (int i = 0; i < 4; ++i) \
-                *buffer++ = (extended_mask | v_buffer_mask.i[i]) & data->gradient.colorTable[index_vec.i[i]].toArgb32(); \
+                *buffer++ = (extended_mask | v_buffer_mask.i[i]) & data->gradient.colorTable32[index_vec.i[i]]; \
         }
 
 #define FETCH_RADIAL_LOOP(FETCH_RADIAL_LOOP_CLAMP) \
diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 05ccff5de0..fb44a7aeb1 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -4138,7 +4138,8 @@ class QGradientCache
     {
         inline CacheInfo(QGradientStops s, int op, QGradient::InterpolationMode mode) :
             stops(qMove(s)), opacity(op), interpolationMode(mode) {}
-        QRgba64 buffer[GRADIENT_STOPTABLE_SIZE];
+        QRgba64 buffer64[GRADIENT_STOPTABLE_SIZE];
+        QRgb buffer32[GRADIENT_STOPTABLE_SIZE];
         QGradientStops stops;
         int opacity;
         QGradient::InterpolationMode interpolationMode;
@@ -4147,7 +4148,9 @@ class QGradientCache
     typedef QMultiHash<quint64, CacheInfo> QGradientColorTableHash;
 
 public:
-    inline const QRgba64 *getBuffer(const QGradient &gradient, int opacity) {
+    typedef QPair<const QRgb *, const QRgba64 *> ColorBufferPair;
+
+    inline ColorBufferPair getBuffer(const QGradient &gradient, int opacity) {
         quint64 hash_val = 0;
 
         const QGradientStops stops = gradient.stops();
@@ -4163,7 +4166,8 @@ public:
             do {
                 const CacheInfo &cache_info = it.value();
                 if (cache_info.stops == stops && cache_info.opacity == opacity && cache_info.interpolationMode == gradient.interpolationMode())
-                    return cache_info.buffer;
+                    return qMakePair(reinterpret_cast<const QRgb *>(cache_info.buffer32),
+                                     reinterpret_cast<const QRgba64 *>(cache_info.buffer64));
                 ++it;
             } while (it != cache.constEnd() && it.key() == hash_val);
             // an exact match for these stops and opacity was not found, create new cache
@@ -4177,14 +4181,18 @@ protected:
     inline void generateGradientColorTable(const QGradient& g,
                                            QRgba64 *colorTable,
                                            int size, int opacity) const;
-    QRgba64 *addCacheElement(quint64 hash_val, const QGradient &gradient, int opacity) {
+    ColorBufferPair addCacheElement(quint64 hash_val, const QGradient &gradient, int opacity) {
         if (cache.size() == maxCacheSize()) {
             // may remove more than 1, but OK
             cache.erase(cache.begin() + (qrand() % maxCacheSize()));
         }
         CacheInfo cache_entry(gradient.stops(), opacity, gradient.interpolationMode());
-        generateGradientColorTable(gradient, cache_entry.buffer, paletteSize(), opacity);
-        return cache.insert(hash_val, cache_entry).value().buffer;
+        generateGradientColorTable(gradient, cache_entry.buffer64, paletteSize(), opacity);
+        for (int i = 0; i < GRADIENT_STOPTABLE_SIZE; ++i)
+            cache_entry.buffer32[i] = cache_entry.buffer64[i].toArgb32();
+        CacheInfo &cache_value = cache.insert(hash_val, cache_entry).value();
+        return qMakePair(reinterpret_cast<const QRgb *>(cache_value.buffer32),
+                         reinterpret_cast<const QRgba64 *>(cache_value.buffer64));
     }
 
     QGradientColorTableHash cache;
@@ -4418,7 +4426,11 @@ void QSpanData::setup(const QBrush &brush, int alpha, QPainter::CompositionMode
             type = LinearGradient;
             const QLinearGradient *g = static_cast<const QLinearGradient *>(brush.gradient());
             gradient.alphaColor = !brush.isOpaque() || alpha != 256;
-            gradient.colorTable = const_cast<QRgba64*>(qt_gradient_cache()->getBuffer(*g, alpha));
+
+            QGradientCache::ColorBufferPair colorBuffers = qt_gradient_cache()->getBuffer(*g, alpha);
+            gradient.colorTable64 = colorBuffers.second;
+            gradient.colorTable32 = colorBuffers.first;
+
             gradient.spread = g->spread();
 
             QLinearGradientData &linearData = gradient.linear;
@@ -4435,7 +4447,11 @@ void QSpanData::setup(const QBrush &brush, int alpha, QPainter::CompositionMode
             type = RadialGradient;
             const QRadialGradient *g = static_cast<const QRadialGradient *>(brush.gradient());
             gradient.alphaColor = !brush.isOpaque() || alpha != 256;
-            gradient.colorTable = const_cast<QRgba64*>(qt_gradient_cache()->getBuffer(*g, alpha));
+
+            QGradientCache::ColorBufferPair colorBuffers = qt_gradient_cache()->getBuffer(*g, alpha);
+            gradient.colorTable64 = colorBuffers.second;
+            gradient.colorTable32 = colorBuffers.first;
+
             gradient.spread = g->spread();
 
             QRadialGradientData &radialData = gradient.radial;
@@ -4456,7 +4472,11 @@ void QSpanData::setup(const QBrush &brush, int alpha, QPainter::CompositionMode
             type = ConicalGradient;
             const QConicalGradient *g = static_cast<const QConicalGradient *>(brush.gradient());
             gradient.alphaColor = !brush.isOpaque() || alpha != 256;
-            gradient.colorTable = const_cast<QRgba64*>(qt_gradient_cache()->getBuffer(*g, alpha));
+
+            QGradientCache::ColorBufferPair colorBuffers = qt_gradient_cache()->getBuffer(*g, alpha);
+            gradient.colorTable64 = colorBuffers.second;
+            gradient.colorTable32 = colorBuffers.first;
+
             gradient.spread = QGradient::RepeatSpread;
 
             QConicalGradientData &conicalData = gradient.conical;