QGraphicsColorizeEffect resizes widgets

Jakob Clausen

Hi all.
I have a vertical navigation menu with six navigation buttons. The height of the navigation menu is exactly six times the height of one button. Both buttons and menu is set to a fixed size.
The menu looks like this.

The top button has a lighter color. Unfortunately the others are a little diffucult to see. If I put a QGraphicsColorizeEffect on the menu. Then it looks like this.

The Graphics effect is there, but only three buttons remain.
I actually set the effect before the first picture, and then i set the strength to zero (which I assume looks the same as no effect?). In the second picture I set the strength to higher than zero.
If I reset the strength to zero, then the effect disappears - as expected - but still only three buttons remain.
The code of the base class looks like this:

#include "TargetFocus.h"
#include "UI.h"
#include <QGraphicsColorizeEffect>
#include <QDebug>

#define ACTIVATE        0.2
#define DEACTIVATE      0
#define ACTIVE_COLOR    "blue" //0x272727

TargetFocus::TargetFocus(QWidget *parent, UI& ui, MainFocus::Position position) :
    QWidget{parent},
    effect(new QGraphicsColorizeEffect),
    position(position)
{
    effect->setColor(ACTIVE_COLOR);
    effect->setStrength(DEACTIVATE);
    setGraphicsEffect(effect);
    connect(ui.mainFocus, &MainFocus::choose, this, &TargetFocus::choose);
}

void TargetFocus::choose(MainFocus::Position target)
{
    if (position == target)
        qDebug() << position;

    if (position == target)
        effect->setStrength(ACTIVATE);
    else
        effect->setStrength(DEACTIVATE);
}

When I run the program, then I get a lot of.

QPainter::begin: A paint device can only be painted by one painter at a time.
QPainter::translate: Painter not active

As application output. These outputs seems to be related to the function call setGraphicsEffect(effect). If I remove that line, then of course nothing happens, but I also do not get these QPainter messages.

What do you think I should do?

Jakob Clausen

@Jakob-Clausen Anyone?

SGaist

Hi,

Do you mean you have that effect once you start changing the effect strength ?

Jakob Clausen

Not at first.
This is the sequence of events:

call constructor
set stength to zero
setEffect on widget
change strength to larger than zero
at the last point problems happen

Jakob Clausen

What does the error messages

QPainter::begin: A paint device can only be painted by one painter at a time.
QPainter::translate: Painter not active

mean?

jsulm

@Jakob-Clausen Do you have more than one painter on same device?

Jakob Clausen

@jsulm Good question. I was wondering the same thing. It looks like a painter is added, when I set the graphics effect. Is this true?
The widget upon which the effect is set, is also added to a qstackedwidget. Could that cause the ... no more than one painter ... thing? If I add the effect to the qstackedwidget aka the parent, then this error also is no more.
But it still does not look right.
Do I need to repaint the widget?

Jakob Clausen

Something else is strange. Maybe a clue?
The navigation looks like it only has three buttons left. But all six of them are there. I can push them all, and the QWidgetStack changes accordingly. So the buttons are where they should be. But it looks like they are not.
And if I remove the effect, then I can make it all look well by calling repaint().

Jakob Clausen

Are there any limitations on the QGraphicsColorizeEffect?
Should it not be possible to just set it on any old widget?

jsulm

@Jakob-Clausen Do you paint manually on that widget (in paintEvent)?

Jakob Clausen

No. I add subwidgets to a layout and thats it.

Jakob Clausen

I think I have found a way through it all. I can create a new widget of the same size and shape, and instead of a QGraphicsColorizeEffect I can use a QOpacityEffect and the move it to cover the navigationbar. But then the navigation wont accept touch events. Any around that?