Turning off background fill on QDialog

Chrisw01

Hi everyone, I have a problem I can't seem to figure out. I have a QDialog which I paint a image on that has transparency in it. When I paint it to the newly created QDialog box I get the image surrounded by a big white square. Apparently QDialog is filling the box with white then my image is painted over it allowing the white to show through the transparency. I have tried setting the setAutoFillBackground() to false no change. If I turn on the WA_TranslucentBackground then the entire image is not drawn. Is there a way to stop the QDialog box from filling itself with a color when created?
Thanks -- Chris

kshegunov

@Chrisw01

WA_PaintOnScreen?

Chrisw01

All that did was not display anything and throw errors in the application output box. Here's what I have so far.

myQDialogBox::DialogBox(QWidget *parent, QString Name) : QDialog(parent) 
{
      setMouseTracking(false);
      setAutoFillBackground(false); 
      setWindowModality(Qt::ApplicationModal);
      activateWindow();

      resize(image->width(), image->Height();
      QPainter p;
      p.setBrush(backgroundRole(), QBrush(*image));
      setPalette(p);
      show();  
}

It all works fine except it draws a white background before it draws my image and shows through the transparent parts of the image.

Thanks -- Chris

kshegunov

@Chrisw01
Hello,

resize(image->width(), image->Height();
QPainter p;
p.setBrush(backgroundRole(), QBrush(*image));
setPalette(p);
show();

You can't do this stuff - neither the painting, nor calling show() - in the constructor. You paint when there's a paint event (i.e. in a QWidget::paintEvent() override), and show() is called from the user of the widget, when the dialog should be shown. But that is after it's fully created.

Chrisw01

I somehow don't see moving the code out of the constructor is going to fix the problem. I will try, but i'll lay odds the dialogs still going to be filled with a color which is what I need to avoid since I'm overlaying a QImage with transparency on it.

kshegunov

@Chrisw01
Perhaps I'm in error, I seem to have been misled by the typo (QPainter, where it should've read QPalette). ~~In any case, can you show the relevant part of the code where you actually paint the image?~~

I'm sorry I seem to have totally misinterpreted what the problem is. I'm not sure that having a texture pattern for a brush supports an alpha channel though, what do you expect to show under the transparent part of the image?

Kind regards.

Chrisw01

@kshegunov

My Bad, it was supposed to be QPalette p;

The part that actually paints the image is

p.setBrush(BackgroundRole(), QImge(*image));

Since the dialog is creating a window, it uses the system colors and creates a window filled with the system color (in my case white) then I overlay the QImage on top of it. (BTW I'm creating a Skinable GUI). If I use the WA_TranslucentBackground Attribute, then there is no white filled screen. However because I set background to Translucent then my setBrush fails because I'm painting to the background.

I would have thought setAutoFillBackground being set to false would have stopped the QDialog from filling its background on creation.

Here's the code.

myDialogBox::DialogBox(QWidget *parent, QString Name) : QDialog(parent)
{
    setMouseTracking(true);
    setAutoFillBackground(false);
    setWindowModality9Qt::ApplicationModal);
    activateWindow();
    setWindowFlags(Qt::Dialog | Qt::FramlessWindowHint);

    QPalette p;
    p.setBrush(BackgroundRole(), QBrush(*Image));
    setPalette(p);

}

kshegunov

@Chrisw01 said:

Since the dialog is creating a window

Do you mean that you're not passing a parent, or what window if that's not what you mean?

I would have thought setAutoFillBackground being set to false would have stopped the QDialog from filling its background on creation.

But even if that were the case, then setting a brush for the background would do nothing, wouldn't it?

Chrisw01

Yes, I am passing it a parent, however the QDialog creates a new window on top of your current window. I pretty much have given up on this now, I even went as far as overloading the paintEvent for the dialog class and painting from within with the same outcome. And perhaps I misunderstood the setAutoFillBackground, I figured its purpose was to fill the background of the window. So for now I'll just remove the transparent section and it works fine.

Thanks!!

kshegunov

@Chrisw01

Yes, I am passing it a parent, however the QDialog creates a new window on top of your current window.

It doesn't create a new window when you pass a parent; Qt's widgets are alien by default. That's why I was asking. If the dialog is a child widget and it doesn't paint anything it will let you see the parent's contents.