An option to create scatter chart with data points not connected with lines

[GajowyJ]

This is:

- [ ] a bug report
- [X] a feature request
- [ ] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

An user can define scatter chart with data points not connected with lines.

What is the current behavior?

Data points are always connected with lines on a scatter chart.

What are the steps to reproduce?

Please provide a Minimal, Complete, and Verifiable example of code that exhibits the issue without relying on an external Excel file or a web server:

<?php

require __DIR__ . '/vendor/autoload.php';

// Create new Spreadsheet object
$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();

// just create any scatter chart 

Which versions of PhpSpreadsheet and PHP are affected?

PHP 8.0.10
PhpSpreadsheet 1.18.0

[GajowyJ]

Proposed solution:

1. In Chart\DataSeriesvalues.php add following code:

class DataSeriesValues
{
	// ...
	private $isLine = TRUE;
	public function isLine(bool $new=NULL) : bool
	{
		if( is_null($new) )
			return $this->isLine;
		$tmp=$this->isLine;
		$this->isLine = $new;
		return $tmp;
	}
	// ...
}

2. In Writer\Xlsx\Chart.php add following code:

private function writePlotGroup( //...
{
	// ...
	//    Formatting for the points
	if ( // ...
	{
		// ...
	}
	if( !$plotSeriesValues->isLine() && $groupType == DataSeries::TYPE_SCATTERCHART )
	{
		$objWriter->startElement('c:spPr');
		$objWriter->startElement('a:ln');
		$objWriter->writeAttribute('w', 0);
		$objWriter->startElement('a:noFill');
		$objWriter->endElement();	// a:noFill
		$objWriter->endElement();	// a:ln
		$objWriter->endElement();	// c:spPr
	}
	// ...
}

[bridgeplayr]

I can verify that these changes produce the desired results. Thank you, @GajowyJ