Painting / moving in a single step to avoid flickering

[nooky59]

As it was not related to an ARGB widget and there is no answer, I start a new short thread to know if there is a solution to this problem.

I will take the shaped clock sample to explain. I've attached the modified code to this message.

Here is what I've had in the shapedclock.h :

protected:
    void timerEvent(QTimerEvent *event); // <==
    void mouseMoveEvent(QMouseEvent *event);
 
private:
    QPoint dragPosition;
    int step; // <==
    QBasicTimer timer; // <==

protected:
    void timerEvent(QTimerEvent *event); // <==
    void mouseMoveEvent(QMouseEvent *event);

private:
    QPoint dragPosition;
    int step; // <==
    QBasicTimer timer; // <==

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Here is what I've had in the shapedclock's constructor

setWindowTitle(tr("Shaped Analog Clock"));
 
step = 0; // <==
this->timer.start(200, this); // <==

setWindowTitle(tr("Shaped Analog Clock"));

step = 0; // <==
this->timer.start(200, this); // <==

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Here is the added timerEvent() method :

void ShapedClock::timerEvent(QTimerEvent *event)
{
	if(event->timerId() == timer.timerId())
	{
		++step;
		resize(width() + step, height() + step);
		update();
	}
	else
		QWidget::timerEvent(event);
}

void ShapedClock::timerEvent(QTimerEvent *event)
{
	if(event->timerId() == timer.timerId())
	{
		++step;
		resize(width() + step, height() + step);
		update();
	}
	else
		QWidget::timerEvent(event);
}

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And finally, here is the added line in resizeEvent for moving the widget on screen :

void ShapedClock::resizeEvent(QResizeEvent * /* event */)
{
	move(x() - 5, y() - 5);

void ShapedClock::resizeEvent(QResizeEvent * /* event */)
{
	move(x() - 5, y() - 5);

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And you will see clearly the clock shaking when resizing / moving.

As I told in my previous post, there is a simple way to deal with it. Defining a larger size QWidget and painting at the correct location. But for a very large widget that can grow by more than 3 times its size and can be shifted by more than 2 times its size, it consume much more memory and perhaps it won't be efficient to deal with a large QWidget even if it contains reserved transparency areas for growing / offseting ?

So, do you think there is a way to paint and move in a single step to avoid dealing with a very large QWidget just to solve this shaking motion ?

Thanks for your answer on this very tricky problem.