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

1 files changed, 7 insertions, 1 deletions

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()) {