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QPainter problem after window refreshment

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tpomorsk

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  • "tpomorsk" started this thread

Posts: 10

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1

Monday, December 19th 2005, 3:42pm

QPainter problem after window refreshment

Hi,
I wrote very basic painting application - when you move your mouse with the button pressed the line is being drawn on the screen.

However I have a problem when the window is refreshed after it was partially hidden (another part was visible all the time). The line which was alerady drawn is refreshed correctly but I can paint only in the area which has been refreshed. The area which was not hidden seems to be "deactivated" (the line which I draw doesn't appear). This "deactivation" is removed when I cover all my window (or minimize it) forcing it be totally refreshed. After that all the lines appear on the screen (even those which were not visible during drawing).

So I wander: Does paintEvent modify something in QPainter instance? Does it change drawing area of my instance pointed by "paint"?

Here is my code:
whiteboard.cpp

Source code

 
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#include "whiteboard.h"
Whiteboard::Whiteboard( QWidget *parent, const char *name ) : QFrame(parent, name)
{
	i_nbLines = 0;
	paint = new QPainter(this);
	pen = new QPen(red, 2);
	paint->setPen(*pen);
}

Whiteboard::~Whiteboard()
{
	delete paint;
}

void Whiteboard::paintEvent(QPaintEvent *)
{
	paint->drawText( rect(), AlignCenter, "The Text" );
	for(int i=0;i<i_nbLines;i++) {
		paint->drawLine(pqt_lineStart[i],pqt_lineEnd[i]);
	}
}

void Whiteboard::mouseMoveEvent(QMouseEvent *e)					// draw line from previous mouse pos to current
{
	qt_currMousePos = e->pos();
	pqt_lineStart[i_nbLines] = qt_prevMousePos;
	pqt_lineEnd[i_nbLines] = qt_currMousePos;
	paint->drawLine(QPoint(0,0),QPoint(100,100));
	paint->drawLine(qt_prevMousePos,qt_currMousePos);
	qt_prevMousePos = qt_currMousePos;
	i_nbLines++;
}

void Whiteboard::mousePressEvent(QMouseEvent *e)				// draw point in current mouse pos
{
	qt_prevMousePos = e->pos();
	pqt_lineStart[i_nbLines] = qt_prevMousePos;
	pqt_lineEnd[i_nbLines] = qt_prevMousePos;
	paint->drawLine(qt_prevMousePos,qt_prevMousePos);
	i_nbLines++;

}


whiteboard.h

Source code

 
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#ifndef WHITEBOARD_H
#define WHITEBOARD_H

#include <qapplication.h>
#include <qpainter.h>
#include <qevent.h>
#include <qpen.h>
#include <qframe.h>


class Whiteboard : public QFrame
{
	Q_OBJECT
public:
	QPoint pqt_lineStart[50000];
	QPoint pqt_lineEnd[50000];
	int i_nbLines;
//	int i_nbPoints;
	QPoint qt_currMousePos;
	QPoint qt_prevMousePos;

	QPainter *paint;
	QPen	 *pen;

	Whiteboard( QWidget *parent=0, const char *name=0 );
	~Whiteboard();
protected:
	void paintEvent(QPaintEvent *);
	void mouseMoveEvent(QMouseEvent *);
	void mousePressEvent(QMouseEvent *);

};

#endif


main.cpp

Source code

 
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#include "whiteboard.h"

int main( int argc, char **argv)
{
	QApplication a(argc, argv);
	Whiteboard w;
	w.setGeometry(100,100,800,800);
	a.setMainWidget( &w);
	w.show();
	return a.exec();
}



Thanks in advance

jacek

Master

  • "jacek" is male

Posts: 2,729

Location: Warsaw, Poland

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2

Monday, December 19th 2005, 5:06pm

RE: QPainter problem after window refreshment

Try creating that QPainter every time you draw something.
You can meet me at Qt Centre - The Ultimate Qt Community site.

tpomorsk

Beginner

  • "tpomorsk" started this thread

Posts: 10

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3

Friday, December 30th 2005, 4:51pm

RE: QPainter problem after window refreshment [SOLVED]

Thanks.
The problem was caused by using DrawLine method inside QPaintEvent. I have no idea why, but as soon as I removed it the window behaved normally. But without DrawLine I had no refreshing so I used QPixmap and bitBlt instead and it works correctly.

Source code

 
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Whiteboard::Whiteboard( QWidget *parent, const char *name ) : QFrame(parent, name)
{
	paint = new QPainter(this);
	pen = new QPen(red, 2);
	qt_pixmap = new QPixmap(this->width(),this->height());
	qt_pixmap->fill(black);
	paint->setPen(*pen);
}

Whiteboard::~Whiteboard()
{
	delete paint;
}

// *********************************************************************************
// Events
// *********************************************************************************
void Whiteboard::paintEvent(QPaintEvent *)
{
	bitBlt(this,0,0,qt_pixmap,0,0);
}

void Whiteboard::resizeEvent(QResizeEvent *e)
{
	QSize newSize = e->size();
	QPixmap *qt_tempPixmap = new QPixmap(newSize.width(),newSize.height());
	qt_tempPixmap->fill(black);
	bitBlt(qt_tempPixmap,0,0,qt_pixmap,0,0);
	delete qt_pixmap;
	qt_pixmap = qt_tempPixmap;
}


void Whiteboard::mouseMoveEvent(QMouseEvent *e)
{
	qt_currMousePos = e->pos();
	paint->drawLine(qt_prevMousePos,qt_currMousePos);
	emit LocalLineDrawn(qt_prevMousePos,qt_currMousePos);
	qt_prevMousePos = qt_currMousePos;
}

void Whiteboard::mousePressEvent(QMouseEvent *e)
{
	qt_prevMousePos = e->pos();
	paint->drawLine(qt_prevMousePos,qt_prevMousePos);
	emit LocalLineDrawn(qt_prevMousePos,qt_prevMousePos);
}

void Whiteboard::mouseReleaseEvent(QMouseEvent *)
{
	bitBlt(qt_pixmap,0,0,this,0,0);
}