A few questions about pdf file generation using render & QPdfWriter & QCustomplot

[jcqtter]

Qt Version ：5.8
OS ： Windows

My Question:

1、
I want to export the entire widget to pdf，I find the render method，So here's the code

QFile file("D:/test.pdf");
file.open(QIODevice::Append);
QPdfWriter* pdf= new QPdfWriter(&file);
pdf->setPageSize(QPagedPaintDevice::A4);
pdf->setResolution(QPrinter::ScreenResolution);
QPainter printpainter;
printpainter.begin(pdf);
double scale = (double)printer->width() / m_wgtRect.width();
printpainter.scale(scale, scale);
m_wgtRect->render(&printpainter);
printpainter.end()

But there are images and qcustomplot in the widget，After they go through render, they will not be clear when zoomed in，So how do I handle images and qcustomplot in render？

2、
Notice the savePdf method in qcustomplot，Look at the source code and found，What he was using was QPrinter & QPainter，I replaced the QPrinter with a QPdfWriter，The text ratio in the generated pdf file is wrong and becomes very large, especially axis labelText，Further trace code I find the difference：

QPrinter* printer = new QPrinter(QPrinter::ScreenResolution);
printer->setOutputFormat(QPrinter::PdfFormat);
printer->setPageSize(QPagedPaintDevice::A4);
printer->setOutputFileName("D://test2.pdf");

QPainter painter2(printer);
auto rt2 = painter2.fontMetrics().boundingRect(0, 0, 0, 0, Qt::TextDontClip, "x");

painter2.end();

and

QPdfWriter* pdf = new QPdfWriter("D://test.pdf");
pdf->setResolution(QPrinter::ScreenResolution);
pdf->setPageSize(QPagedPaintDevice::A4);
	
QPainter painter1(pdf);
auto rt1 = painter1.fontMetrics().boundingRect(0, 0, 0, 0, Qt::TextDontClip, "x");

painter1.end();

Just use a different device to initialize QPainter，The rect of the resulting font is different：
Use QPrinter ： （0,0,6,12）
Use QPdfWriter： （0,0,75,150）
Even if the setFont method is used to modify the font of QPdfWriter, it will not work，So, how can QPdfWriter get the same font rect as QPrinter？

Best wishes