Repainting widget

[fear]

My widget doesn't repaint correctly. I have no idea why.

Step 1:


Step 2:


Step 3:

[...]
 
class MainWindow : public QMainWindow
{
	Q_OBJECT
 
	public:
		MainWindow();
		MainWindow(QWidget * parent, const char * name);
		~MainWindow();
 
	public slots:
		void clearFill();
		void clear();
		void reset();
 
	protected:
		void paintEvent(QPaintEvent * e);
		void mouseMoveEvent(QMouseEvent * e);
		void mousePressEvent(QMouseEvent * e);
		void mouseDoubleClickEvent(QMouseEvent * e);
 
	private:
		Painter * painter;
 
[...]
 
void MainWindow::paintEvent(QPaintEvent * e)
{
	painter->repaint();
 
	QMainWindow::paintEvent(e);
}
 
[...]
 
class Painter
{
	public:
		[...]
 
	private:
		[...]
		QPainter * painter;
 
[...]
 
void Painter::repaint()
{
	for (int i = 0 ; i != width ; i++)
	{
		for (int j = 0 ; j != height ; j++)
			drawPoint(array[i][j]);
	}
 
	for (SimpleSegmentList::iterator i = list.begin() ; i != list.end() ; i++)
		drawLine((*i));
}
 
[...]
 
void Painter::drawPoint(const Point & p)
{
	if (!painter)
		return;
 
	painter->setPen(QPen(QColor(0, 0, 0)));
	painter->setBrush(QBrush(p.color()));
	painter->drawEllipse(p.center().x(), p.center().y(), p.dia(), p.dia());
}
 
void Painter::drawLine(const SimpleSegment & s)
{
	if (!painter)
		return;
 
	const int hdia = array[0][0].dia() / 2;
 
	QPoint start = point(s.start()).center();
	QPoint stop = point(s.stop()).center();
 
	start.setX(start.x() + hdia);
	start.setY(start.y() + hdia);
	stop.setX(stop.x() + hdia);
	stop.setY(stop.y() + hdia);
 
	painter->setPen(QPen(s.color(), hdia));
	painter->drawLine(start, stop);
}
 
[...]

[...]

class MainWindow : public QMainWindow
{
	Q_OBJECT

	public:
		MainWindow();
		MainWindow(QWidget * parent, const char * name);
		~MainWindow();

	public slots:
		void clearFill();
		void clear();
		void reset();

	protected:
		void paintEvent(QPaintEvent * e);
		void mouseMoveEvent(QMouseEvent * e);
		void mousePressEvent(QMouseEvent * e);
		void mouseDoubleClickEvent(QMouseEvent * e);

	private:
		Painter * painter;

[...]

void MainWindow::paintEvent(QPaintEvent * e)
{
	painter->repaint();

	QMainWindow::paintEvent(e);
}

[...]

class Painter
{
	public:
		[...]
		
	private:
		[...]
		QPainter * painter;

[...]

void Painter::repaint()
{
	for (int i = 0 ; i != width ; i++)
	{
		for (int j = 0 ; j != height ; j++)
			drawPoint(array[i][j]);
	}

	for (SimpleSegmentList::iterator i = list.begin() ; i != list.end() ; i++)
		drawLine((*i));
}

[...]

void Painter::drawPoint(const Point & p)
{
	if (!painter)
		return;

	painter->setPen(QPen(QColor(0, 0, 0)));
	painter->setBrush(QBrush(p.color()));
	painter->drawEllipse(p.center().x(), p.center().y(), p.dia(), p.dia());
}

void Painter::drawLine(const SimpleSegment & s)
{
	if (!painter)
		return;

	const int hdia = array[0][0].dia() / 2;

	QPoint start = point(s.start()).center();
	QPoint stop = point(s.stop()).center();
	
	start.setX(start.x() + hdia);
	start.setY(start.y() + hdia);
	stop.setX(stop.x() + hdia);
	stop.setY(stop.y() + hdia);

	painter->setPen(QPen(s.color(), hdia));
	painter->drawLine(start, stop);
}

[...]

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[Stukfruit]

No idea, but here's a few brainfarts from when I read your sample code:

- Is your Painter a subclass from QPainter?
- Try to rename your repaint method to something else..

[wysota]

You have to create a new painter during each paint event and I don't see that in your code.

[fear]

Thank You. That's true. In fact api doc doesn't say it in explicit way. I was always using QPainter in this way:

Mostly, all this is done inside a paint event. (In fact, 99% of all QPainter use is in a reimplementation of QWidget::paintEvent(), and the painter is heavily optimized for such use.) Here's one very simple example:

void SimpleExampleWidget::paintEvent()
    {
        QPainter paint( this );
        paint.setPen( Qt::blue );
        paint.drawText( rect(), AlignCenter, "The Text" );
    }

void SimpleExampleWidget::paintEvent()
    {
        QPainter paint( this );
        paint.setPen( Qt::blue );
        paint.drawText( rect(), AlignCenter, "The Text" );
    }

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So now I realized that it MUST be used in such way.