Graph plotting

[steg90]

Hi,

I've come up with the following simple code to draw a x,y graph plot ( the graph is updated in real-time ) :

void PlotterView::paintEvent( QPaintEvent *event)
{
	QPainter painter(this);
 
	painter.setWindow( 0, 0, 800, 200 );
 
	painter.setRenderHint( QPainter::Antialiasing, true);
	painter.setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::RoundCap, Qt::MiterJoin));
 
	int nGridStep = 20;
	for( int x = 0; x <= 800 / nGridStep; x ++ )
	{
		painter.drawLine( x * nGridStep, 0, x * nGridStep, 200 );	
	}
	for( int y = 0; y <= 200 / nGridStep; y ++ )
	{
		painter.drawLine( 0, y * nGridStep, 800, y * nGridStep );	
	}
 
	painter.setPen(QPen(Qt::red, 3, Qt::SolidLine, Qt::RoundCap, Qt::MiterJoin));
	int nSpace = 0;
	int nSpace2 = 0;
	for( int i = 0; i < 48; i ++ )  // size of linear buffer
	{
		nSpace += nGridStep;
		painter.drawLine( nSpace2, 200 - m_GraphArray[ i ], nSpace, 200 - m_GraphArray[ i + 1 ] );
		nSpace2 += nGridStep;
	}
}

void PlotterView::paintEvent( QPaintEvent *event)
{
	QPainter painter(this);

	painter.setWindow( 0, 0, 800, 200 );

	painter.setRenderHint( QPainter::Antialiasing, true);
	painter.setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::RoundCap, Qt::MiterJoin));

	int nGridStep = 20;
	for( int x = 0; x <= 800 / nGridStep; x ++ )
	{
		painter.drawLine( x * nGridStep, 0, x * nGridStep, 200 );	
	}
	for( int y = 0; y <= 200 / nGridStep; y ++ )
	{
		painter.drawLine( 0, y * nGridStep, 800, y * nGridStep );	
	}

	painter.setPen(QPen(Qt::red, 3, Qt::SolidLine, Qt::RoundCap, Qt::MiterJoin));
	int nSpace = 0;
	int nSpace2 = 0;
	for( int i = 0; i < 48; i ++ )  // size of linear buffer
	{
		nSpace += nGridStep;
		painter.drawLine( nSpace2, 200 - m_GraphArray[ i ], nSpace, 200 - m_GraphArray[ i + 1 ] );
		nSpace2 += nGridStep;
	}
}

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m_GraphArray is an array of unsigned ints which gets updated as a 'rolling buffer', at the moment, the graph is plotting randomly within a timer :

void PlotterView::timerEvent(QTimerEvent *event)
{
	memcpy( m_GraphArray, &m_GraphArray[1], 50 * sizeof(unsigned int) );   // move entire array left one
	m_GraphArray[50] = qrand() % 200;     
	repaint();
}

void PlotterView::timerEvent(QTimerEvent *event)
{
	memcpy( m_GraphArray, &m_GraphArray[1], 50 * sizeof(unsigned int) );   // move entire array left one
	m_GraphArray[50] = qrand() % 200;     
	repaint();
}

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What I like about this, is the fact that if the user stretches the window this widget is in, the graph also stretches etc...

Ok, now my question, finally... If I wanted to have other controls within the window the graph is in, how do I do it so when the user stretches the window, the graph doesn't go over these controls? Does this make sense?!

I was thinking I may have a subclassed label or something and use that to draw the graph on and just drop this onto a new window?

Regards,
Steve

PS - If there is also a better way of drawing graphs instead of using the QPainter class I'd be very interested.

[magland]

Ok, now my question, finally... If I wanted to have other controls within the window the graph is in, how do I do it so when the user stretches the window, the graph doesn't go over these controls? Does this make sense?!

Make a layout and insert the plot window and the controls as separate components and then set the size policies appropriately.

PS - If there is also a better way of drawing graphs instead of using the QPainter class I'd be very interested.

Use QwtPlot from the Qwt library.

You may also want to have a look at ChainLink.

[steg90]

Hi,

Thanks, the QwtPlot looks the way to go. I am using Windows, I guess I will beed to compile this library in order to use it?

Regards,
Steve

[magland]

Hi,

Thanks, the QwtPlot looks the way to go. I am using Windows, I guess I will beed to compile this library in order to use it?

Regards,
Steve

Three steps to using qwt:
1. Compile the library (qmake and make)
2. Link against the library (in your project file, using LIBS += ...)
3. #include the appropriate qwt headers in your code, for example "qwt_plot.h"

You will probably be interested in QwtPlot and QwtPlotCurve

[steg90]

Thanks,

I've tried to compile the library but not having any luck, I'm doing this for Win32. Maybe I need to convert the .pro files? I'm using MSVC.

Regards,
Steve

[magland]

Thanks,

I've tried to compile the library but not having any luck, I'm doing this for Win32. Maybe I need to convert the .pro files? I'm using MSVC.

Regards,
Steve

Try looking at http://docs.huihoo.com/qwt/qwtinstall.html.

[steg90]

Thanks, this is what I have been looking at, but still no success

Regards,
Steve

[steg90]

Cannot find certain header files when I'm compiling the libs, these are in my path

Header files such as sal.h, math.h...

I'd like to get this to build, it sounds ideal.

Regards,
Steve

[steg90]

Hi,

Having installed QWT library, I now do the following code :

QwtPlot *myPlot;
	myPlot = new QwtPlot(this);

QwtPlot *myPlot;
	myPlot = new QwtPlot(this);

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What happens when the new is called is my application just quits, anybody any ideas, I'm thinking maybe some DLL missing or something?

Regards,
Steve

[steg90]

I decided to build QWT again but this time with the examples, the library builds fine but I cannot build the examples, this is the error after I run nmake :

Microsoft (R) Program Maintenance Utility Version 8.00.50727.762
Copyright (C) Microsoft Corporation. All rights reserved.

link /LIBPATH:"c:\Qt\4.3.0\lib" /LIBPATH:"c:\Qt\4.3.0\lib" /NOLOGO /DEBU
G /MANIFESTFILE:"obj\cpuplot.intermediate.manifest" /SUBSYSTEM:WINDOWS /OUT:debu
g\cpuplot.exe @C:\DOCUME~1\STEVEG~1.DIA\LOCALS~1\Temp\nmD2.tmp
moc_cpuplot.obj : error LNK2001: unresolved external symbol "public: static stru
ct QMetaObject const QwtPlot::staticMetaObject" (?staticMetaObject@QwtPlot@@2UQM
etaObject@@B)
debug\cpuplot.exe : fatal error LNK1120: 1 unresolved externals
NMAKE : fatal error U1077: '"C:\Program Files\Microsoft Visual Studio 8\VC\BIN\l
ink.EXE"' : return code '0x460'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files\Microsoft Visual Studio 8\VC\BIN\n
make.exe"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: 'cd' : return code '0x2'
Stop.
NMAKE : fatal error U1077: 'cd' : return code '0x2'
Stop.

As can be seen, it looks like it isn't linking in the qwt5.lib file, do I need to path this or something?

Any help is appreciated,
Steve

[steg90]

Hi,

I'm using Qwt to help me with plotting graph data. What I want is to allow the user to zoom in and out of the graph. I have been looking at the QwtPlotZoomer class and implemented the following code:

QwtPlotZoomer* zoomer = new QwtPlotZoomer(QwtPlot::xBottom,
									QwtPlot::yLeft,
									QwtPicker::DragSelection,
									QwtPicker::AlwaysOn,
									myPlot->canvas() );
	zoomer->setRubberBandPen(QPen(Qt::black));
	zoomer->setZoomBase();

QwtPlotZoomer* zoomer = new QwtPlotZoomer(QwtPlot::xBottom,
									QwtPlot::yLeft,
									QwtPicker::DragSelection,
									QwtPicker::AlwaysOn,
									myPlot->canvas() );
	zoomer->setRubberBandPen(QPen(Qt::black));
	zoomer->setZoomBase();

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I was expecting to be able to left click the mouse and produce a rectangle over the graph which would then zoom in, on right click it would zoom out. What do I need in order to implement this?

Any help is appreciated,
Regards,
Steve

[sincnarf]

Cannot find certain header files when I'm compiling the libs, these are in my path

Header files such as sal.h, math.h...

I'd like to get this to build, it sounds ideal.

Regards,
Steve

Hello Steg90 Have you installed qwt successfully and actually ran a program using it?

I'm trying to install QWT can you teach me or give me a complete guide how you made qwt work for you?

[swathi]

hey
when i excuted the above code
i have got the errors
can u pls tell me which header files to be included
and the start of the program

[ningoji]

Hi..
How can i plot graph in QT.I have to take data from a file and have to plot