QRasterPixmapData: Reuse underlying QImage in fill() if possible.

When switching from a format without alpha channel to one that has it,
reuse the underlying QImage memory if the old & new color depths match.

This avoids one allocation when using the rather common pattern:

    QPixmap pixmap(w, h);
    pixmap.fill(Qt::transparent);

Reviewed-by: Samuel Rødal

3 files changed, 46 insertions, 40 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index d86021cb9..747dd2f 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -139,42 +139,6 @@ QImageData::QImageData()
 {
 }
 
-static int depthForFormat(QImage::Format format)
-{
-    int depth = 0;
-    switch(format) {
-    case QImage::Format_Invalid:
-    case QImage::NImageFormats:
-        Q_ASSERT(false);
-    case QImage::Format_Mono:
-    case QImage::Format_MonoLSB:
-        depth = 1;
-        break;
-    case QImage::Format_Indexed8:
-        depth = 8;
-        break;
-    case QImage::Format_RGB32:
-    case QImage::Format_ARGB32:
-    case QImage::Format_ARGB32_Premultiplied:
-        depth = 32;
-        break;
-    case QImage::Format_RGB555:
-    case QImage::Format_RGB16:
-    case QImage::Format_RGB444:
-    case QImage::Format_ARGB4444_Premultiplied:
-        depth = 16;
-        break;
-    case QImage::Format_RGB666:
-    case QImage::Format_ARGB6666_Premultiplied:
-    case QImage::Format_ARGB8565_Premultiplied:
-    case QImage::Format_ARGB8555_Premultiplied:
-    case QImage::Format_RGB888:
-        depth = 24;
-        break;
-    }
-    return depth;
-}
-
 /*! \fn QImageData * QImageData::create(const QSize &size, QImage::Format format, int numColors)
 
     \internal
@@ -195,7 +159,7 @@ QImageData * QImageData::create(const QSize &size, QImage::Format format, int nu
 
     uint width = size.width();
     uint height = size.height();
-    uint depth = depthForFormat(format);
+    uint depth = qt_depthForFormat(format);
 
     switch (format) {
     case QImage::Format_Mono:
@@ -871,7 +835,7 @@ QImageData *QImageData::create(uchar *data, int width, int height,  int bpl, QIm
         return 0;
     }
 
-    const int depth = depthForFormat(format);
+    const int depth = qt_depthForFormat(format);
     const int calc_bytes_per_line = ((width * depth + 31)/32) * 4;
     const int min_bytes_per_line = (width * depth + 7)/8;
 
@@ -6321,7 +6285,7 @@ int QImage::bitPlaneCount() const
         bpc = 12;
         break;
     default:
-        bpc = depthForFormat(d->format);
+        bpc = qt_depthForFormat(d->format);
         break;
     }
     return bpc;
diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index c687448..e054814 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -112,6 +112,42 @@ struct Q_GUI_EXPORT QImageData {        // internal image data
 
 void qInitImageConversions();
 
+inline int qt_depthForFormat(QImage::Format format)
+{
+    int depth = 0;
+    switch(format) {
+    case QImage::Format_Invalid:
+    case QImage::NImageFormats:
+        Q_ASSERT(false);
+    case QImage::Format_Mono:
+    case QImage::Format_MonoLSB:
+        depth = 1;
+        break;
+    case QImage::Format_Indexed8:
+        depth = 8;
+        break;
+    case QImage::Format_RGB32:
+    case QImage::Format_ARGB32:
+    case QImage::Format_ARGB32_Premultiplied:
+        depth = 32;
+        break;
+    case QImage::Format_RGB555:
+    case QImage::Format_RGB16:
+    case QImage::Format_RGB444:
+    case QImage::Format_ARGB4444_Premultiplied:
+        depth = 16;
+        break;
+    case QImage::Format_RGB666:
+    case QImage::Format_ARGB6666_Premultiplied:
+    case QImage::Format_ARGB8565_Premultiplied:
+    case QImage::Format_ARGB8555_Premultiplied:
+    case QImage::Format_RGB888:
+        depth = 24;
+        break;
+    }
+    return depth;
+}
+
 QT_END_NAMESPACE
 
 #endif
diff --git a/src/gui/image/qpixmap_raster.cpp b/src/gui/image/qpixmap_raster.cpp
index 53f3559..65c0344 100644
--- a/src/gui/image/qpixmap_raster.cpp
+++ b/src/gui/image/qpixmap_raster.cpp
@@ -206,7 +206,13 @@ void QRasterPixmapData::fill(const QColor &color)
                 else
 #endif
                     toFormat = QImage::Format_ARGB32_Premultiplied;
-                image = QImage(image.width(), image.height(), toFormat);
+
+                if (!image.isNull() && qt_depthForFormat(image.format()) == qt_depthForFormat(toFormat)) {
+                    image.detach();
+                    image.d->format = toFormat;
+                } else {
+                    image = QImage(image.width(), image.height(), toFormat);
+                }
             }
 
             switch (image.format()) {