#280 Regression in log scale engine in 6.1.3

[Elvis Stansvik]

Hi Uwe,

I recently upgraded my application from 6.1.2 to 6.1.3 and noticed a regression in how curves with 0 values are plotted with the logarithmic scale engine, when the plot axis scale is set manually.

Here's the test case:

main.cpp

#include <QApplication>

#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_scale_engine.h>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QwtPlot plot;

    QwtPlotCurve curve("Test Curve");
    curve.setSamples({ 0, 0, 0.01, 0.02, 0.01, 0.02, 0, 0 }, { 0, 1, 2, 3, 4, 5, 6, 7 });
    curve.attach(&plot);

    plot.setAxisScaleEngine(QwtPlot::xBottom, new QwtLogScaleEngine());
    plot.setAxisScale(QwtPlot::xBottom, 0.00001, 1, 2);
    plot.show();

    return app.exec();
}

logtest.pro

TEMPLATE = app
CONFIG += c++11
TARGET = logtest
INCLUDEPATH += .

# Edit to point at your Qwt
#include(qwt-6.1.2-svn/features/qwt.prf)
include(qwt-6.1.3-svn/features/qwt.prf)
#include(qwt-6.3.0-svn/features/qwt.prf)

SOURCES += main.cpp

And here's the result with 6.1.2 and 6.1.3:

Result with 6.1.2

Result with 6.1.3

Notice the strange result with 6.1.3. I get this result with trunk as well.

I think this may be related to r2446, but I'm not sure.

[Anonymous]

it is not a bug, log(0) is not defined

[Anonymous]

Right, it's just that we found Qwt's behavior in earlier versions in dealing with log(0) during plotting was convenient for our purposes. But I realize now we shouldn't rely on this. Will close the bug.

[Elvis Stansvik]

Sorry forgot to log in while posting my reply. It's in moderation now.