QPainter::drawPixmap behaves different on Windows and Linux

[kshahar]

I'm trying to draw a transparent PNG file inside a QWidget. The problem is, I'm getting different results on Windows and Linux.
Windows screenshot: screenshot-windows.jpg
Linux screenshot: screenshot-linux.jpg
The difference could be seen easily. I cannot upload the actual image because the forum breaks it, and it's not allowed to link to external websites.

The code I used for testing is -

class TestWidget: public QWidget {
public:
    TestWidget(const char* imagePath)
    {
        m_pixmap = QPixmap(imagePath);
        setStyleSheet("background-color: black");
    }
 
protected:
    virtual void paintEvent(QPaintEvent *)
    {
        QPainter painter(this);
        painter.drawPixmap(QPoint(0,0), m_pixmap);
    }
 
    QPixmap m_pixmap;
};

class TestWidget: public QWidget {
public:
    TestWidget(const char* imagePath)
    {
        m_pixmap = QPixmap(imagePath);
        setStyleSheet("background-color: black");
    }

protected:
    virtual void paintEvent(QPaintEvent *)
    {
        QPainter painter(this);
        painter.drawPixmap(QPoint(0,0), m_pixmap);
    }

    QPixmap m_pixmap;
};

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And the main function looks like this:

TestWidget* testWidget = new TestWidget(imagePath);
testWidget->setGeometry(0, 10, 1024, 1024);
testWidget->show();

TestWidget* testWidget = new TestWidget(imagePath);
testWidget->setGeometry(0, 10, 1024, 1024);
testWidget->show();

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I'm using Qt 4.5.1/4.7.2, Windows XP and CentOS 5.5.

Any ideas what could be the problem?

[ChrisW67]

Is one defaulting to anti-aliasing and the other not? Perhaps the difference is in the pixmap scaling options. Have you tried explicitly setting rendering settings with QPainter::setRenderHint()?

Also have a read under Rendering Quality in the QPainter docs.