Grid Minor Major and gap before the data

[viridis]

Hi,

I don't want any spacing between the scale backbone and the canvas (plotting area). Thus, the backbones of the left and bottom axes should be "connected". I tried the following without success (there is a 1 or 2 pixels gap):

plotLayout()->setAlignCanvasToScales(true);
plotLayout()->setCanvasMargin(0, QwtPlot::xBottom);
plotLayout()->setCanvasMargin(0, QwtPlot::xTop);
plotLayout()->setCanvasMargin(0, QwtPlot::yLeft);
plotLayout()->setCanvasMargin(0, QwtPlot::yRight);
plotLayout()->setSpacing(0);
plotLayout()->setMargin(0);

plotLayout()->setAlignCanvasToScales(true);
plotLayout()->setCanvasMargin(0, QwtPlot::xBottom);
plotLayout()->setCanvasMargin(0, QwtPlot::xTop);
plotLayout()->setCanvasMargin(0, QwtPlot::yLeft);
plotLayout()->setCanvasMargin(0, QwtPlot::yRight);
plotLayout()->setSpacing(0);
plotLayout()->setMargin(0);

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Any hints?