Mac: pixmaps dont treat alpha exactly the same as other platforms

From fixing qwidget autotest, it seems to be the case that filling
a pixmap with a solid color on mac changes the hasAlpha status. This
is different from X11 (and raster engine). That is, the following
code will produce different result:

QPixmap pixmap(100, 100);
pixmap.setAlphaChannel(QPixmap(100, 100));
qDebug() << "Has alpha after setting channel?" << pixmap.hasAlpha();
pixmap.fill(Qt::red);
qDebug() << "Has alpha after fill?" << pixmap.hasAlpha();

So, this patch remove the possibility of converting an already alpha
supporting pixmap to non-alpha upon fill. NB: somewhat related, the
following code works the same on both x11, raster and mac (prints
'false'), but still seems wrong:

QPixmap pixmap2(pixmap);
qDebug() << "pixmap2 has alpha initially?" << pixmap2.hasAlpha();

Rev-By: Fabien Freling

1 files changed, 5 insertions, 1 deletions

diff --git a/src/gui/image/qpixmap_mac.cpp b/src/gui/image/qpixmap_mac.cpp
index 31aa192..f152718 100644
--- a/src/gui/image/qpixmap_mac.cpp
+++ b/src/gui/image/qpixmap_mac.cpp
@@ -413,7 +413,11 @@ void QMacPixmapData::fill(const QColor &fillColor)
                 *(dptr + i) = colr;
         }
     }
-    macSetHasAlpha(fillColor.alpha() != 255);
+
+    // If we had an alpha channel from before, don't
+    // switch it off. Only go from no alpha to alpha:
+    if (fillColor.alpha() != 255)
+        macSetHasAlpha(true);
 }
 
 QPixmap QMacPixmapData::alphaChannel() const