Qpainter function on a QFrame problem

[impeteperry]

i am doing a total re-write of a Qt3 program in Qt4
I am using Kubuntu 7.10 distro.
I have a QFrame area "frameA" that I want to use for my drawing (QpaintEvent ).
My Code:

void BaseForm::paintEvent ( QPaintEvent  * event )
{
	QString k, h;
	double angle;
	int n, xs, xe, ys, ye, xc, yc;
	bool ok;
	QPainter p ( this );
 
	QPen pen;
	QFont f;
 
	if ( paintSupportLines.count () > 0 )
	{
		f.setFamily ( "Courier" );
		f.setPointSize ( dwgScaleFactor );
		p.setFont ( f );
		pen.setBrush ( Qt::blue );
		p.setPen ( pen );				
		p.setViewport ( viewportRect );
		p.setWindow ( windowRect );
 
		if ( clearWindow == "erase" ) { p.eraseRect ( windowRect ); clearWindow = "cancel erase"; }
		else
		{
			for ( n = 0; n < paintSupportLines.count(); ++n )
			{
				p.setClipRect ( clippingRect );
				k = paintSupportLines[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				p.drawLine ( xs, ys, xe, ye );

void BaseForm::paintEvent ( QPaintEvent  * event )
{
	QString k, h;
	double angle;
	int n, xs, xe, ys, ye, xc, yc;
	bool ok;
	QPainter p ( this );

	QPen pen;
	QFont f;

	if ( paintSupportLines.count () > 0 )
	{
		f.setFamily ( "Courier" );
		f.setPointSize ( dwgScaleFactor );
		p.setFont ( f );
		pen.setBrush ( Qt::blue );
		p.setPen ( pen );				
		p.setViewport ( viewportRect );
		p.setWindow ( windowRect );

		if ( clearWindow == "erase" ) { p.eraseRect ( windowRect ); clearWindow = "cancel erase"; }
		else
		{
			for ( n = 0; n < paintSupportLines.count(); ++n )
			{
				p.setClipRect ( clippingRect );
				k = paintSupportLines[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				p.drawLine ( xs, ys, xe, ye );

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etc. I can single step thru the program, all values seem correct.,
Since I want to have my graphics in the "frameA" area of the screen I thought maybe I should change line #7 to "QPainter p( frameA )". but this did not help.

The code samples in "The Book of Qt 4" uses separate classes for their "QPaintEvent"s
Do I have to do that?

I would appreciate some help as I am at a total loss.

thanks

[jpn]

If you want to draw on frameA, you must reimplement its paintEvent() instead of some other widget's paintEvent(), here BaseForm. In other words, you must implement paintEvent() of the widget you draw on.

[impeteperry]

Thanks,
I am not sure on how to "reimplement its paintEvent()
I have

void BaseForm::slotSetPaintItems ( QStringList list )
{
	QString k;
	int n ;
 
	for ( n = 0; n < list.count(); ++n )
	{
		tempList = list[n].split ( "|" );		/// split the list into types of stringLists
		k = tempList[0];	/// get the type of element to draw
		if(k == "erase") 			clearWindow = "erase";
		else
		{
			tempList.removeFirst();															/// remove the element with the code
			if(k == "supports")	paintSupportLines = tempList;		///
			else if (k == "columns") paintColumns = tempList;
			else if(k == "erase") clearWindow = "true";
		}
	}
	BaseForm::update();																/// now update it.
}

void BaseForm::slotSetPaintItems ( QStringList list )
{
	QString k;
	int n ;

	for ( n = 0; n < list.count(); ++n )
	{
		tempList = list[n].split ( "|" );		/// split the list into types of stringLists
		k = tempList[0];	/// get the type of element to draw
		if(k == "erase") 			clearWindow = "erase";
		else
		{
			tempList.removeFirst();															/// remove the element with the code
			if(k == "supports")	paintSupportLines = tempList;		///
			else if (k == "columns") paintColumns = tempList;
			else if(k == "erase") clearWindow = "true";
		}
	}
	BaseForm::update();																/// now update it.
}

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Is this where I would do it if I knew How??
My original "frameA"

frameA = new QFrame ( this );
	frameA->setFrameShape ( QFrame::StyledPanel );
	frameA->setAutoFillBackground ( true );
	frameA->setPalette ( QColor ( 255, 255, 235 ) );
	frameA->setFrameShadow ( QFrame::Raised );

frameA = new QFrame ( this );
	frameA->setFrameShape ( QFrame::StyledPanel );
	frameA->setAutoFillBackground ( true );
	frameA->setPalette ( QColor ( 255, 255, 235 ) );
	frameA->setFrameShadow ( QFrame::Raised );

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Again I would appreciate your help
pete

[jpn]

Just like BaseForm does it. Subclass QFrame and reimplement paintEvent(). Again, BaseForm cannot paint on QFrame when BaseForm happens to receive a paint event. QFrame must do painting itself whenever it receives a paint event.

[impeteperry]

Thanks again, but I am a very old tired frustrated engineer. Please give me the code to do this as everytime I try the program locks up.
thanks

Hold up I think I found what you are talking about. I will let you know how I make out.

[impeteperry]

I'm back.
I have not been able to make any headway. I have loaded examples from "Programming with Qt4", "The Book of Qt4". I have added all kinds of widgets to my QFrame frameA.
I have QPainter p( to all kinds of stuff ) .I can change size, add colors etc. But NO LINES!!
In Qt3 I had no trouble, even rendering solids, but not in Qt4.

I know it must be a very simple thing, but if you don't know it.......

I would love to see a simple working example that shows exactly what is necessary for drawing a line on a QFrame widget.

thanks

[jpn]

I have QPainter p( to all kinds of stuff )

You just can't paint on whatever widget you like to. You can't write

QPainter p(someOtherWidgetSomewhere);

QPainter p(someOtherWidgetSomewhere);

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but you make the some other widget somewhere do

QPainter p(this);

QPainter p(this);

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in its own paintEvent().

I would love to see a simple working example that shows exactly what is necessary for drawing a line on a QFrame widget.

As I said, you must subclass QFrame and reimplement paintEvent()

class MyCustomFrame : public QFrame
{
   ...
protected:
    void paintEvent(QPaintEvent* event); // <-- a reimplemented method
};
 
MyCustomFrame::paintEvent(QPaintEvent* event)
{
    QPainter painter(this); // <-- look, i can paint on myself
    ...
}

class MyCustomFrame : public QFrame
{
   ...
protected:
    void paintEvent(QPaintEvent* event); // <-- a reimplemented method
};

MyCustomFrame::paintEvent(QPaintEvent* event)
{
    QPainter painter(this); // <-- look, i can paint on myself
    ...
}

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[impeteperry]

Hi, I have

#ifndef MYCUSTOMFRAME_H
#define MYCUSTOMFRAME_H
 
#include "baseform.h"
#include <qframe.h>
#include <qpainter.h>
 
 
class MyCustomFrame : public QFrame
{
	Q_OBJECT
 
	protected:
		void paintEvent(QPaintEvent* event);
};
 
void MyCustomFrame::paintEvent(QPaintEvent* event)
{
		QPainter painter(this);
	painter.drawLine(0, 0, 200, 150);
}
 
#endif	// MYCUSTOMFRAME_H

#ifndef MYCUSTOMFRAME_H
#define MYCUSTOMFRAME_H

#include "baseform.h"
#include <qframe.h>
#include <qpainter.h>


class MyCustomFrame : public QFrame
{
	Q_OBJECT

	protected:
		void paintEvent(QPaintEvent* event);
};

void MyCustomFrame::paintEvent(QPaintEvent* event)
{
		QPainter painter(this);
	painter.drawLine(0, 0, 200, 150);
}

#endif	// MYCUSTOMFRAME_H

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and it compiles with out errors or warnings.
I have 2 quentions:
1. How do I access it from the body of my program as I was required to remove "#include "mycustomframe.h" from "baseform.cpp"?

2. I have a class "drawingfunctions.h" where I would like to do the painting. If I read you correctly, I need to change the class name from

class DrawingFunctions : public QWidget
{
	Q_OBJECT
 
public:

class DrawingFunctions : public QWidget
{
	Q_OBJECT

public:

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to

class DrawingFunctions : public QFrame
{
	Q_OBJECT
 
public:
	DrawingFunctions( QWidget *parent = 0 );

class DrawingFunctions : public QFrame
{
	Q_OBJECT

public:
	DrawingFunctions( QWidget *parent = 0 );

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and i think the "parent = 0" is wrong.
And what do I need to change here?

DrawingFunctions::DrawingFunctions( QWidget *parent ) :  QWidget(parent)

DrawingFunctions::DrawingFunctions( QWidget *parent ) :  QWidget(parent)

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As you can tell, i have no clear understanding of whats going on. I am able to use QTextEdit widgets on my base QFrame, but not the QPainter.
(These "uncontrolled" events of Qt4 are driving me up a wall.)

I really appreciate your patience with me.

[impeteperry]

I never have had as much trouble with anything I can remember.
As you suggested I setup a new class "MyDrawingFrame" and implemented it as best as I could. It compiles without any warnings

#ifndef MYDRAWINGFRAME_H
#define MYDRAWINGFRAME_H
 
#include "baseform.h"
#include <qframe.h>
#include <qpainter.h>
 
class MyDrawingFrame : public  QFrame
{
	Q_OBJECT
 
public:
 
public slots:
 
protected:
	void paintEvent(QPaintEvent * event);
 
protected slots:
 
private:
	QStringList tempList;
	QStringList paintSupportLines;
	QStringList paintColumns;
	QString clearWindow;
 
	QRect  viewportRect;
	QRect  windowRect;
	QRect clippingRect;
	double pi;
	int activeLevel;
	int functionNumber;
	int dwgScaleFactor;
	int count;
	int num;
	int n;
	int o1;
 
	bool ok;
 
private slots:
 
signals:
 
};
 
void MyDrawingFrame::paintEvent(QPaintEvent * event)
{
	QString k, h;
	double angle;
	int n, xs, xe, ys, ye, xc, yc;
	bool ok;
 
	QPainter p(this);
	QPen pen;
	QFont f;
 
	if ( paintSupportLines.count () > 0 )
	{
		f.setFamily ( "Courier" );
		f.setPointSize ( dwgScaleFactor );
		p.setFont ( f );
		pen.setBrush ( Qt::blue );
		p.setPen ( pen );
		p.setViewport ( viewportRect );
		p.setWindow ( windowRect );
 
		if ( clearWindow == "erase" ) { p.eraseRect ( windowRect ); clearWindow = "cancel erase"; }
		else
		{
			for ( n = 0; n < paintSupportLines.count(); ++n )
			{
				//teErrorMessages->setText("F5 key clicked");
				p.setClipRect ( clippingRect );
				k = paintSupportLines[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				p.drawLine ( 10, 10 * n, 200, 200 );
				p.drawLine ( xs, ys, xe, ye );
						/// start of labeling.
				if ( tempList[4] == "true" )
				{
					p.setClipRect ( windowRect );
					xc = ( xs + xe ) / 2;
					yc = ( ys + ye ) / 2;
					if ( xs == xe ) angle = pi/2.0;
					else if ( ys == ye ) angle = 0.0;
					else
					{
//					angle = atan((double)(ye-ys)/(xe-xs));			/// Why did Qt 4 drop trig functions????
						angle = ( double ) ( ye-ys ) / ( xe-xs );		/// hope this works!!!
						angle /= 2.0 * pi ;
					}
					angle = ( angle * 180.0 ) / pi;
					p.save();
					p.translate ( xc, yc );
					p.rotate ( angle );	//teErrorMessages->setText("F5 key clicked");
					p.scale ( 1, -1 );
					k = "S" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
					p.restore();
				}
			}
		}
		if ( paintColumns.count() > 0 )
		{
			p.setViewport ( viewportRect );
			p.setWindow ( windowRect );
			p.setClipRect ( windowRect );
			for ( n = 0; n < paintColumns.count(); ++n )
			{
				k = paintColumns[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				angle = tempList[4].toInt ( &ok );
				p.save();
				p.translate ( xs, ys );
				p.rotate ( angle );
				p.fillRect ( -xe/2, -ye/2, xe, ye, Qt::black );
				if ( tempList[5] == "true" )
				{
					f.setFamily ( "Courier" );
					f.setPointSize ( ( int ) ( .8 * dwgScaleFactor ) );
					p.setFont ( f );
					pen.setBrush ( Qt::black );
					p.setPen ( pen );
					p.rotate ( -angle + 25 );
					p.scale ( 1, -1 );
					k = "---C" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
				}
				p.restore();
			}
		}
	}
}
#endif	// MYDRAWINGFRAME_H

#ifndef MYDRAWINGFRAME_H
#define MYDRAWINGFRAME_H

#include "baseform.h"
#include <qframe.h>
#include <qpainter.h>

class MyDrawingFrame : public  QFrame
{
	Q_OBJECT

public:

public slots:

protected:
	void paintEvent(QPaintEvent * event);

protected slots:

private:
	QStringList tempList;
	QStringList paintSupportLines;
	QStringList paintColumns;
	QString clearWindow;

	QRect  viewportRect;
	QRect  windowRect;
	QRect clippingRect;
	double pi;
	int activeLevel;
	int functionNumber;
	int dwgScaleFactor;
	int count;
	int num;
	int n;
	int o1;

	bool ok;

private slots:

signals:

};

void MyDrawingFrame::paintEvent(QPaintEvent * event)
{
	QString k, h;
	double angle;
	int n, xs, xe, ys, ye, xc, yc;
	bool ok;

	QPainter p(this);
	QPen pen;
	QFont f;

	if ( paintSupportLines.count () > 0 )
	{
		f.setFamily ( "Courier" );
		f.setPointSize ( dwgScaleFactor );
		p.setFont ( f );
		pen.setBrush ( Qt::blue );
		p.setPen ( pen );
		p.setViewport ( viewportRect );
		p.setWindow ( windowRect );

		if ( clearWindow == "erase" ) { p.eraseRect ( windowRect ); clearWindow = "cancel erase"; }
		else
		{
			for ( n = 0; n < paintSupportLines.count(); ++n )
			{
				//teErrorMessages->setText("F5 key clicked");
				p.setClipRect ( clippingRect );
				k = paintSupportLines[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				p.drawLine ( 10, 10 * n, 200, 200 );
				p.drawLine ( xs, ys, xe, ye );
						/// start of labeling.
				if ( tempList[4] == "true" )
				{
					p.setClipRect ( windowRect );
					xc = ( xs + xe ) / 2;
					yc = ( ys + ye ) / 2;
					if ( xs == xe ) angle = pi/2.0;
					else if ( ys == ye ) angle = 0.0;
					else
					{
//					angle = atan((double)(ye-ys)/(xe-xs));			/// Why did Qt 4 drop trig functions????
						angle = ( double ) ( ye-ys ) / ( xe-xs );		/// hope this works!!!
						angle /= 2.0 * pi ;
					}
					angle = ( angle * 180.0 ) / pi;
					p.save();
					p.translate ( xc, yc );
					p.rotate ( angle );	//teErrorMessages->setText("F5 key clicked");
					p.scale ( 1, -1 );
					k = "S" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
					p.restore();
				}
			}
		}
		if ( paintColumns.count() > 0 )
		{
			p.setViewport ( viewportRect );
			p.setWindow ( windowRect );
			p.setClipRect ( windowRect );
			for ( n = 0; n < paintColumns.count(); ++n )
			{
				k = paintColumns[n];
				tempList = k.split ( "," );
				xs = tempList[0].toInt ( &ok );
				ys = tempList[1].toInt ( &ok );
				xe = tempList[2].toInt ( &ok );
				ye = tempList[3].toInt ( &ok );
				angle = tempList[4].toInt ( &ok );
				p.save();
				p.translate ( xs, ys );
				p.rotate ( angle );
				p.fillRect ( -xe/2, -ye/2, xe, ye, Qt::black );
				if ( tempList[5] == "true" )
				{
					f.setFamily ( "Courier" );
					f.setPointSize ( ( int ) ( .8 * dwgScaleFactor ) );
					p.setFont ( f );
					pen.setBrush ( Qt::black );
					p.setPen ( pen );
					p.rotate ( -angle + 25 );
					p.scale ( 1, -1 );
					k = "---C" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
				}
				p.restore();
			}
		}
	}
}
#endif	// MYDRAWINGFRAME_H

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Great, but how do I access it to set the values of the variables and activate the paint event itself??. If I "#include "mydrawingframe.h" in my "baseframe.cpp" or anyplace else for that matter I get an

/home/pete/Desktop/pm-straight-C/pm/mydrawingframe.h:65: multiple definition of `MyDrawingFrame:aintEvent(QPaintEvent*)'
baseform.o:/home/pete/Desktop/pm-straight-C/pm/mydrawingframe.h:65: first defined here
collect2: ld returned 1 exit status
make: *** [pm] Error 1

I have also tried setting up a "mydrawingframe.cpp" but I could not get a "MyDrawingFrame::MydrawingFrame( Q??? *parent ) : Q???
t(parent) that did not give an error when compiling.
Sorry to be so long winded, but I am desperate. What in H--- am I missing??? All I want to do is draw some lines of a QFrame widget!!!!!

[wysota]

Have you seen this thread?

http://www.qtcentre.org/forum/f-qt-d...bel-11504.html

Especially take a look at how the line is drawn depending on the size of the widget.

[impeteperry]

Thanks Mysota It was a great help.My big problem I forgot the line under the "public;" when defining the class. What ever you do, don't get old (I'm 81).

Now all I have to do is figure out how to set the size of the frame, but I"m going to bed it's 12:30.

Thanks again.

[ashukla]

Thanks Mysota It was a great help.My big problem

Please mention the name correctly as Wysota, Qt Guru.

[impeteperry]

Wysots, Qi Guru, I'm sorry about the name. It was late and I don't see to well.
I have made some progress. I can draw some lines, so I am back at setting up my scaling functions.
I do have a question. In the distant past I wrote to a "pixmap". is there any advantage to that now with the paintEvent functionallity?
Thanks

[impeteperry]

Hi
I now have my painter working on my laptop whereI compiled the program.
It also runs on my desk computer as long as I don't re-compile it there. If I re-compile the same source code there it locks up the computer on the first "p.drawText" command. I have single stepped the program on both computers. Everything is the same. There is no problem with the "p.drawLine" command. If I option out the single p.drawText(x, y, "text"); line 16, the program runs fine.

p.drawLine ( xs, ys, xe, ye );
						/// start of labeling.
				if ( tempList[4] == "true" )
				{
					xc = ( xs + xe ) / 2;
					yc = ( ys + ye ) / 2;
					if ( xs == xe ) angle = pi/2.0;
					else if ( ys == ye ) angle = 0.0;
					else	angle = atan((double)(ye - ys) / (double)(xe - xs));
					angle = ( angle * 180.0 ) / pi;
					p.save();
					p.translate ( xc, yc );
					p.rotate ( angle );
					p.scale ( 1, -1 );
					k = "S" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
					p.restore();
				}

p.drawLine ( xs, ys, xe, ye );
						/// start of labeling.
				if ( tempList[4] == "true" )
				{
					xc = ( xs + xe ) / 2;
					yc = ( ys + ye ) / 2;
					if ( xs == xe ) angle = pi/2.0;
					else if ( ys == ye ) angle = 0.0;
					else	angle = atan((double)(ye - ys) / (double)(xe - xs));
					angle = ( angle * 180.0 ) / pi;
					p.save();
					p.translate ( xc, yc );
					p.rotate ( angle );
					p.scale ( 1, -1 );
					k = "S" + h.setNum ( n + 1 );
					p.drawText ( 0, 0, k );
					p.restore();
				}

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I am using the same Kubuntu 7.10 on each computer.
I am sorry to be such a pest.
Thanks for help.

[wysota]

What exactly is the widget supposed to display?

[impeteperry]

I have a bunch of lines and i label them with their number. the text I want to display is "S1" See attachment. These are "Grid" lines are used for locating building columns and other elements.
Except for the screen size the data is identical on the two computers. The lines draw correctly so the "viewWindow" and "viewPort" are set correctly. If I take the compiled program from the second machine, it runes fine on the firsrt machine.

In essense, the program compiled on the first computer runs fine on both computers
The program compiled on the second computer locks it up when run, but runs fine on the first computer.

[wysota]

Why don't you use QGraphicsView to make the visualization?

[impeteperry]

QGraphicsView was add in Qt4.2. I was unaware of its existance
Thanks, I will take a look at it.

[impeteperry]

I took a quick look at your QGraphicView and found

By default, the items are drawn onto the viewport by using a regular QPainter, and using default render hints.

What would be the advantage using this when I already have the geometry and am already using the "painter" to draw items onto the "viewPort"?

[wysota]

Ease of handling. I don't say you should take that approach, but that if you have problems with one mechanism, try using another.