QGraphicsDropShadowEffect causing a QPainter error

**Berryblue031** · 18th March 2011, 13:38

Has anybody come across

QGraphicsDropShadowEffect throwing the following error?

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

I am adding a bit of flourish in my app and when I try to put a dropshadow on widgets that are in a QStackedWidget (I am not sure if this is what is causing the crash) I am getting a crash in

void QGraphicsDropShadowEffect::draw(QPainter *painter)

**JohannesMunk** · 20th March 2011, 00:32

Could you create and post a minimal example application that shows the error?

Joh

**Berryblue031** · 23rd March 2011, 10:35

Unfortunately when I try to reproduce it in a minimal example it doesn't happen, but in my main app it is still there. Can you think of any general scenarios that could trigger something like this?

Added after 1 4 minutes:

Also it only happens when I am mousing over the shadowed widget if I just switch between them in the stack panel everything is fine, but something that happens when mousing over triggers the paint errors.

**Sparhawk** · 27th March 2011, 18:43

I have the same problem with QGraphicsOpacityEffect on a QStackedWidget. I try to extend QStackedWidget to get fade effects or transitions when you change the page (using currentIndex) on QStackedWidget. But I can't reproduce on a small application.

This is the code of the extenden QStackedWidget. Are there something wrong?

Qt Code:

Switch view

#ifndef GRAPHICSSTACKEDWIDGET_H
#define GRAPHICSSTACKEDWIDGET_H
 
#include <QStackedWidget>
 
class GraphicsStackedWidgetPrivate;
 
class GraphicsStackedWidget : public QStackedWidget
{
	Q_OBJECT
	Q_PROPERTY (int currentIndex READ currentIndex WRITE setCurrentIndex)
	Q_PROPERTY (double windowOpacity READ windowOpacity WRITE setWindowOpacity DESIGNABLE isWindow)
 
private:
	GraphicsStackedWidgetPrivate *d;
	Q_DECLARE_PRIVATE(GraphicsStackedWidget)
 
public:
	GraphicsStackedWidget(QWidget *parent = 0);
	~GraphicsStackedWidget();
 
	int currentIndex() const;
	Q_INVOKABLE int addWidget(QWidget *w);
 
public slots:
 
private slots:
	void setCurrentIndex ( int index );
	bool hidePage();
	void showPage();
};
 
#endif // GRAPHICSSTACKEDWIDGET_H
 
-----------------------------------------------------------
 
#include "graphicsstackedwidget.h"
#include <QtGui>
#include <QGraphicsLinearLayout>
 
#define TRANSITION_TIME_MS	500
 
class GraphicsStackedWidgetPrivate
{
public:
	int m_index;
	GraphicsStackedWidgetPrivate() {
	}
};
 
 
GraphicsStackedWidget::GraphicsStackedWidget(QWidget *parent):
		QStackedWidget(parent),
		d(new GraphicsStackedWidgetPrivate)
{
	d->m_index = 0;
}
 
GraphicsStackedWidget::~GraphicsStackedWidget()
{
	delete d;
}
 
int GraphicsStackedWidget::currentIndex() const
{
	return QStackedWidget::currentIndex();
}
 
void GraphicsStackedWidget::setCurrentIndex ( int index )
{
	d->m_index = index;
	if ( hidePage() ) {
		QTimer::singleShot(TRANSITION_TIME_MS/2, this, SLOT(showPage()));
	} else {
		showPage();
	}
}
 
int GraphicsStackedWidget::addWidget(QWidget *w)
{
	return QStackedWidget::addWidget(w);
}
 
bool GraphicsStackedWidget::hidePage()
{
	bool result = false;
	QWidget *oldWidget = QStackedWidget::widget(QStackedWidget::currentIndex());
	if ( oldWidget != NULL ) {
		QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect(oldWidget);
		oldWidget->setGraphicsEffect(effect);
		QPropertyAnimation *animation = new QPropertyAnimation(effect, "opacity", this);
		animation->setDuration(TRANSITION_TIME_MS/2);
		animation->setStartValue(1);
		animation->setEndValue(0);
		animation->start();
		QTimer::singleShot(TRANSITION_TIME_MS/2, oldWidget, SLOT(repaint()));
		result = true;
	}
	return result;
}
 
void GraphicsStackedWidget::showPage()
{
	QWidget *widget = QStackedWidget::widget(d->m_index);
	if ( widget != NULL ) {
		QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect(widget);
		widget->setGraphicsEffect(effect);
		QPropertyAnimation *animation = new QPropertyAnimation(effect, "opacity", this);
		animation->setDuration(TRANSITION_TIME_MS/2);
		animation->setStartValue(0);
		animation->setEndValue(1);
		animation->start();
		QTimer::singleShot(TRANSITION_TIME_MS/2, widget, SLOT(repaint()));
	}
	QStackedWidget::setCurrentIndex(d->m_index);
	if ( widget != NULL ) {
		widget->update();
	}
}

#ifndef GRAPHICSSTACKEDWIDGET_H
#define GRAPHICSSTACKEDWIDGET_H

#include <QStackedWidget>

class GraphicsStackedWidgetPrivate;

class GraphicsStackedWidget : public QStackedWidget
{
	Q_OBJECT
	Q_PROPERTY (int currentIndex READ currentIndex WRITE setCurrentIndex)
	Q_PROPERTY (double windowOpacity READ windowOpacity WRITE setWindowOpacity DESIGNABLE isWindow)

private:
	GraphicsStackedWidgetPrivate *d;
	Q_DECLARE_PRIVATE(GraphicsStackedWidget)

public:
	GraphicsStackedWidget(QWidget *parent = 0);
	~GraphicsStackedWidget();

	int currentIndex() const;
	Q_INVOKABLE int addWidget(QWidget *w);

public slots:

private slots:
	void setCurrentIndex ( int index );
	bool hidePage();
	void showPage();
};

#endif // GRAPHICSSTACKEDWIDGET_H

-----------------------------------------------------------

#include "graphicsstackedwidget.h"
#include <QtGui>
#include <QGraphicsLinearLayout>

#define TRANSITION_TIME_MS	500

class GraphicsStackedWidgetPrivate
{
public:
	int m_index;
	GraphicsStackedWidgetPrivate() {
	}
};


GraphicsStackedWidget::GraphicsStackedWidget(QWidget *parent):
		QStackedWidget(parent),
		d(new GraphicsStackedWidgetPrivate)
{
	d->m_index = 0;
}

GraphicsStackedWidget::~GraphicsStackedWidget()
{
	delete d;
}

int GraphicsStackedWidget::currentIndex() const
{
	return QStackedWidget::currentIndex();
}

void GraphicsStackedWidget::setCurrentIndex ( int index )
{
	d->m_index = index;
	if ( hidePage() ) {
		QTimer::singleShot(TRANSITION_TIME_MS/2, this, SLOT(showPage()));
	} else {
		showPage();
	}
}

int GraphicsStackedWidget::addWidget(QWidget *w)
{
	return QStackedWidget::addWidget(w);
}

bool GraphicsStackedWidget::hidePage()
{
	bool result = false;
	QWidget *oldWidget = QStackedWidget::widget(QStackedWidget::currentIndex());
	if ( oldWidget != NULL ) {
		QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect(oldWidget);
		oldWidget->setGraphicsEffect(effect);
		QPropertyAnimation *animation = new QPropertyAnimation(effect, "opacity", this);
		animation->setDuration(TRANSITION_TIME_MS/2);
		animation->setStartValue(1);
		animation->setEndValue(0);
		animation->start();
		QTimer::singleShot(TRANSITION_TIME_MS/2, oldWidget, SLOT(repaint()));
		result = true;
	}
	return result;
}

void GraphicsStackedWidget::showPage()
{
	QWidget *widget = QStackedWidget::widget(d->m_index);
	if ( widget != NULL ) {
		QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect(widget);
		widget->setGraphicsEffect(effect);
		QPropertyAnimation *animation = new QPropertyAnimation(effect, "opacity", this);
		animation->setDuration(TRANSITION_TIME_MS/2);
		animation->setStartValue(0);
		animation->setEndValue(1);
		animation->start();
		QTimer::singleShot(TRANSITION_TIME_MS/2, widget, SLOT(repaint()));
	}
	QStackedWidget::setCurrentIndex(d->m_index);
	if ( widget != NULL ) {
		widget->update();
	}
}

To copy to clipboard, switch view to plain text mode

Thanks a lot