How QT exports data to PDF files (qpdfwriter User Guide)

When using some text editing software , We may often encounter “ Output is PDF”, How on earth did it happen ？ This article will use QPdfWriter + QPainter, Realize the QGradient::Preset Corresponding color rendering , Export to PDF file . Here is the sample code ：

1、 Sample code

QString pdfName = "QGradientPreset";
pdfName.append(QDateTime::currentDateTime().toString("yyyyMMdd-HHmmss"));
pdfName.append(".pdf");
QString filePath = QFileDialog::getSaveFileName(this, QStringLiteral(" export QGradient Default "), pdfName, "*.pdf");
if (filePath.isEmpty()) {
    
	return;
}

//
QFile pdfFile(filePath);
if (!pdfFile.open(QIODevice::WriteOnly)) {
    
	return;
}
QPdfWriter* pdfWriter = new QPdfWriter(&pdfFile);
// initialization QPdfWriter
pdfWriter->setPageSize(QPagedPaintDevice::A4);
pdfWriter->setResolution(300); // Set up dpi( It's usually 96)
pdfWriter->setPageMargins(QMargins(30, 30, 30, 30));

// draw PDF Content 
QPainter* painter = new QPainter(pdfWriter);
painter->setRenderHint(QPainter::Antialiasing);
int pdfWidth = painter->viewport().width();
int pdfHeight = painter->viewport().height();

int colorIndex = 0;
int posTop = 0;
int posLeft = 0;
int width = 530;// Color block width 
int height = 180;// Color block height 
int margin = 20;// Color block spacing 

// Draw title text 
painter->setFont(QFont("NSimSun", 20, QFont::Normal));
painter->drawText(QRect(posLeft, posTop, pdfWidth, height),
	Qt::AlignCenter,
	QString::fromLocal8Bit("QGradient Preset  Color value comparison chart "));

// The starting ordinate of the color block 
posTop += height;

//paint begin
while (colorIndex < 180)//QGradient::Preset::NumPresets - 1
{
    
	colorIndex++;
	//
	QGradient::Preset clr = QGradient::Preset(colorIndex);
	painter->fillRect(QRect(posLeft, posTop, width, height), clr);
	//
	painter->setFont(QFont("NSimSun", 14, QFont::Normal));
	painter->drawText(QRect(posLeft, posTop, width, height),
		Qt::AlignCenter, 
		QString::fromLocal8Bit("Preset: %1").arg(colorIndex));

	posLeft += (width + margin);
	int posRight = posLeft + width;
	if (posRight >= pdfWidth)
	{
    
		posLeft = 0;
		//
		posTop += (height + margin);
		int posButtom = posTop + height;
		if (posButtom >= pdfHeight)
		{
    
			pdfWriter->newPage();
			posTop = 0;
		}
	}
}
//paint end

//delete it
delete painter;
delete pdfWriter;
pdfFile.close();

//
QDesktopServices::openUrl(QUrl::fromLocalFile(filePath));

2、 Output pdf The contents of the document

3、 other

Qt Web page links provided by assistants ：https://webgradients.com/
another ： The included header file required in the code , Please add your own .