Drawing a QLinearGradient in a QImage

TanEk

Hi,

I am trying to render a gradient into an image to save it in a file. I am doing this:

@
const int histogramSize = 256;
QLinearGradient gradient(0, 0, histogramSize, 0);
gradient.setStops(stops);

    QImage lut = QImage(QSize(1, histogramSize), QImage::Format_ARGB32);
    QPainter p(&lut);
    p.setCompositionMode(QPainter::CompositionMode_Source);
    p.fillRect(0, 0, histogramSize, 1, gradient);

    const uchar * buffer = lut.bits();
    const int nbOfBytes = histogramSize * 4 ;
    assert(nbOfBytes == lut.byteCount());
    const uchar * endBuffer = buffer + nbOfBytes;
    QColor begin(lut.pixel(QPoint(0, 0)));
    QColor end(lut.pixel(QPoint(0, histogramSize - 1)));
    for(int i = 0 ; i < 2 ; ++i)
    {
        QColor color = stops[i].second;
        std::cout << i << ": " << color.red() << ' ' << color.green() << ' ' << color.blue() << ' ' << color.alpha() << '\n';
    }
    std::cout << "begin: " << begin.red() << ' ' << begin.green() << ' ' << begin.blue() << ' ' << begin.alpha() << '\n';
    std::cout << "end: " << end.red() << ' ' << end.green() << ' ' << end.blue() << ' ' << end.alpha() << '\n';

@

And the gradient is defined by two points like you can see in the screenshot

http://s2.postimage.org/7uipuh5it/Screen_Hunter_01_May_13_16_15.jpg

The result of the program is:

bq. 0: 252 252 252 2
1: 252 252 252 252
begin: 255 255 255 255
end: 205 205 205 255

However as you can see begin doesn't have the alpha value I am expecting of them. I tried to change the RGB components and they change properly like I expect them to be but the alpha component never change. It is almost like if the gradient didn't care on changing the alpha component even if I set the composition mode to source which should basically just dump the gradient into the image. Is it a bug or is it the normal behavior and if it is the normal behavior could someone explain me why?

Thanks

YuriyRusinov

Could you update reference to screenshot ? When I try to see, I receive an error "Image not available"

YuriyRusinov

Could you update reference to screenshot ? When I try to see, I receive an error "Image not available"

andre

The original post was over three years old, by a user who only made this one post. Please don't try to revive the dead...

andre

The original post was over three years old, by a user who only made this one post. Please don't try to revive the dead...