Print a graph

? Offline

I found this code on internet:
https://www.qcustomplot.com/index.php/support/forum/976

it works but I want to paint only the graph without the side dish for the printer..on a dockwidget..so I tried to write:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPrintDialog>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow),
mPlot(new QCustomPlot(this))
{
ui->setupUi(this);

setCentralWidget(mPlot);

// just setting up a plot, nothing special happening here:
mPlot->axisRect()->setupFullAxesBox(true);
mPlot->addGraph()->addData(QVector<double>() << 1 << 2 << 3 << 4, QVector<double>() << 1 << 2 << 4 << 8);
mPlot->rescaleAxes();
mPlot->legend->setVisible(true);
mPlot->axisRect()->insetLayout()->setInsetAlignment(0, Qt::AlignLeft|Qt::AlignTop); // align legend to top left corner

ui->menuBar->addAction("Print Preview", this, SLOT(printPreview()));
}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::printPreview()
{
QDockWidget dock;
// QPrinter printer;
//QPrintPreviewDialog previewDialog(&dock, this);
//dock.setFloating(true);
//dock.show();
//dock.setFloating(true);
connect(&dock, SIGNAL(paintRequested(QDockWidget*)), SLOT(renderPlot(QDockWidget*)));

dock.show();
}

void MainWindow::renderPlot(QDockWidget * dock)
{
//printer->setPageSize(QPrinter::A4);
QCPPainter painter(dock);
//dock->setFloating(true);
//QRectF pageRect = printer->pageRect(QPrinter::DevicePixel);

int plotWidth = mPlot->viewport().width();
int plotHeight = mPlot->viewport().height();
// double scale = pageRect.width()/(double)plotWidth;

painter.setMode(QCPPainter::pmVectorized);
painter.setMode(QCPPainter::pmNoCaching);
painter.setMode(QCPPainter::pmNonCosmetic); // comment this out if you want cosmetic thin lines (always 1 pixel thick independent of pdf zoom level)

//painter.scale(scale, scale);
mPlot->toPainter(&painter, plotWidth, plotHeight);
dock->show();
//dock->setFloating(true);
}

but It doesn't work..I want only to have a copy of the graph in a dockwidget and not the side dish gray