Qt-interest Archive, February 2007
Alpha channel in Pixmap used to work
Message 1 in thread
Hi Qt experts,
I used to work with Qt with qt-x11-free-3.3.5 about a half year ago. The
program I worked on at that time was a kind of graphic program which
based on handling images with alpha channel (PNG). Deciding that I will
improve my program I started to use the latest qt-x11-free edition the
qt-x11-free-3.3.7. (I deliberately use Qt 3 because Qt 4 proved to be
slower in drawing.) The following code worked perfectly with qt 3.3.5 it
worked as I expected, but the compiling it with qt.3.3.7 did not yield
the desired result, that is the alpha blending did not work.
QPixmap image1("image_no_alpha.png");
QPixmap image2("image_with_alpha.png");
QPainter painter();
painter.begin(this);
.
.
painter.drawPixmap(0,0,image1);
painter.drawPixmap(0,0,image2);
.
.
painter.end();
image2.hasAlphaChannel() returns false, which makes me think that the
alpha channel information is destroyed when creating image2.
Unfortunatelly I don't have my previous configuration.
An important information that I compiled the qt framework -static option
in both case. Running the program compiled with qt 3.3.5 works perfectly
in my present configuration, that is alpha channel handling works, but
when I compile it with 3.3.7 the result makes me feel blue. The only
difference between my present and my former configuration beside the
version of Qt is that I am using now Xorg instead of Xfree86.
A new thought has just came to my mind, I remember that I compiled qt
3.3.5 with -system-libpng switch. But I am not entirely sure in this.
Maybe could it cause that alpha channel does not work now?
Has anybody an idea of the root of the failure, because I am completely
desperated related to this issue. Why did it use to work, and why do not
work it now?
Please help, any idea will be appreciated highly.
Best Regards:
Krisztian
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