QwtPlot, problem with large plotwidth

Dear all,

I have to plot a curve with - lets say - 40000 (or more) points. The solution I found is to do this in a QScrollArea. For the first 32800 (round about) points this works very good and I can scroll (x-axis) my curve without problems. But for points greater than 32800 the area is just black. Please see the code below to reproduce the behaviour. (I am using Opensuse 13.1 64bit, qwt-6.1.2, qt-4.8.5). Thanks in advance for your help.

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#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qwt_plot_canvas.h>
#include <qwt_plot_layout.h>
#include <qwt_scale_engine.h>
#include <qapplication.h>
#include <qscrollarea.h>
#include <QAbstractScrollArea>
#include <QVBoxLayout>
#include <QLabel>
#include <qmainwindow.h>
#include <math.h>

#define PLOTWIDTH 40000

int main(int argc, char **argv)
{
QApplication my_qt_app(argc, argv);
double x[PLOTWIDTH];
double y[PLOTWIDTH];
int i;

for (i=0;i<PLOTWIDTH;i++) {
x[i] = (double) i;
y[i] = sin(((double)i * M_PI)/180.);
}

QWidget mainw;
QVBoxLayout *mainLayout = new QVBoxLayout(&mainw);

QScrollArea *sau = new QScrollArea();
sau->setMinimumSize(1000, 420);

QwtPlot *plotu = new QwtPlot();
plotu->setFixedSize(PLOTWIDTH, 400);
plotu->setAxisScale(QwtPlot::xBottom,0,PLOTWIDTH,100);
plotu->setPalette( Qt::gray );
plotu->setCanvasBackground( Qt::white);

QwtPlotCurve *my_curve = new QwtPlotCurve();
my_curve->setRawSamples(x, y, PLOTWIDTH);
my_curve->setPen(* new QPen(QColor(0xff,0x10,0))); /* red */
my_curve->attach(plotu);
sau->setWidget(plotu);
mainLayout->addWidget(sau);

mainw.show();
return my_qt_app.exec();
}
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I would strongly discourage your QScrollArea approach - you will run into many, many problems with this huge widget - better use the approach you find in the realtime example ( zoom in and you will see scrollbars ).
Concerning the 32800 I would guess that you find a limitation somewhere because of unsigned shorts.

Uwe

Thanks Uwe,

BR
Walter