Making pixels semi-transparent

Question

I am trying to make some pixels semi-transparent.

Using a QPainter with pen color Qt::color0 and Qt::color1 works to make pixels fully transparent or opaque, but I tried to set the pen color to 0.5 to make a partially transparent pixel, but it does not work as I would expect.

In this example, the opaque pixels are red, the transparent pixels are white (the color of the background, and I would expect the semitransparent pixels to be pink, but they are also white:

http://programmingexamples.net/index.php?title=Qt/Images/SemiTransparentPixels

Can anyone see where I have gone wrong?

In your code, the line painter.setPen(.5); is probably not doing what you expect it to do. You need to do something like painter.setPen( QColor( 255, 0, 0, 127 ) ); like Stephen Chu suggested — Tim Meyer

Stephen Chu Stephen Chu · Accepted Answer · 2011-11-15T02:28:04

2

votes

Set alpha to 0.5 (127) in your QColor: http://doc.qt.io/qt-4.8/qcolor.html#QColor-2

Making pixels semi-transparent

1 Answers