Support Bezier Curve and Scaling of X-Axis on Scatter Plot

For Bezier, need to specify `<c:smooth>` tag in addition to already supplied `<c:scatterStyle val="smoothMarker">`

For X-Axis, scatter needs to supply both X and y axis as `<c:valAx>` rather than `<c:catAx>` for X.

src/PhpSpreadsheet/Chart/DataSeriesValues.php

@@ -27,7 +27,7 @@ class DataSeriesValues
     /**
      * Series Data Source.
      *
-     * @var string
+     * @var ?string
      */
     private $dataSource;
 
@@ -95,7 +95,7 @@ class DataSeriesValues
      * @param null|string|string[] $fillColor
      * @param string $pointSize
      */
-    public function __construct($dataType = self::DATASERIES_TYPE_NUMBER, $dataSource = '', $formatCode = null, $pointCount = 0, $dataValues = [], $marker = null, $fillColor = null, $pointSize = '3')
+    public function __construct($dataType = self::DATASERIES_TYPE_NUMBER, $dataSource = null, $formatCode = null, $pointCount = 0, $dataValues = [], $marker = null, $fillColor = null, $pointSize = '3')
     {
         $this->setDataType($dataType);
         $this->dataSource = $dataSource;
@@ -144,7 +144,7 @@ public function setDataType($dataType)
     /**
      * Get Series Data Source (formula).
      *
-     * @return string
+     * @return ?string
      */
     public function getDataSource()
     {
@@ -154,7 +154,7 @@ public function getDataSource()
     /**
      * Set Series Data Source (formula).
      *
-     * @param string $dataSource
+     * @param ?string $dataSource
      *
      * @return $this
      */

src/PhpSpreadsheet/Writer/Xlsx/Chart.php

@@ -306,7 +306,7 @@ private function writePlotArea(XMLWriter $objWriter, PlotArea $plotArea, ?Title
             if ($chartType === DataSeries::TYPE_BUBBLECHART) {
                 $this->writeValueAxis($objWriter, $xAxisLabel, $chartType, $id1, $id2, $catIsMultiLevelSeries, $xAxis, $majorGridlines, $minorGridlines);
             } else {
-                $this->writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $catIsMultiLevelSeries, $xAxis);
+                $this->writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $catIsMultiLevelSeries, $xAxis, ($chartType === DataSeries::TYPE_SCATTERCHART) ? 'c:valAx' : 'c:catAx');
             }
 
             $this->writeValueAxis($objWriter, $yAxisLabel, $chartType, $id1, $id2, $valIsMultiLevelSeries, $yAxis, $majorGridlines, $minorGridlines);
@@ -367,9 +367,9 @@ private function writeDataLabels(XMLWriter $objWriter, ?Layout $chartLayout = nu
      * @param string $id2
      * @param bool $isMultiLevelSeries
      */
-    private function writeCategoryAxis(XMLWriter $objWriter, ?Title $xAxisLabel, $id1, $id2, $isMultiLevelSeries, Axis $yAxis): void
+    private function writeCategoryAxis(XMLWriter $objWriter, ?Title $xAxisLabel, $id1, $id2, $isMultiLevelSeries, Axis $yAxis, string $element = 'c:catAx'): void
     {
-        $objWriter->startElement('c:catAx');
+        $objWriter->startElement($element);
 
         if ($id1 > 0) {
             $objWriter->startElement('c:axId');
@@ -1202,6 +1202,11 @@ private function writePlotGroup(?DataSeries $plotGroup, string $groupType, XMLWr
 
                 $this->writePlotSeriesValues($plotSeriesValues, $objWriter, $groupType, 'num');
                 $objWriter->endElement();
+                if ($groupType === DataSeries::TYPE_SCATTERCHART && $plotGroup->getPlotStyle() === 'smoothMarker') {
+                    $objWriter->startElement('c:smooth');
+                    $objWriter->writeAttribute('val', '1');
+                    $objWriter->endElement();
+                }
             }
 
             if ($groupType === DataSeries::TYPE_BUBBLECHART) {

tests/PhpSpreadsheetTests/Writer/Xlsx/Charts32XmlTest.php

@@ -0,0 +1,89 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PhpOffice\PhpSpreadsheet\Shared\File;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx as XlsxWriter;
+use PHPUnit\Framework\TestCase;
+
+class Charts32XmlTest extends TestCase
+{
+    // These tests can only be performed by examining xml.
+    private const DIRECTORY = 'samples' . DIRECTORY_SEPARATOR . 'templates' . DIRECTORY_SEPARATOR;
+
+    /** @var string */
+    private $outputFileName = '';
+
+    protected function tearDown(): void
+    {
+        if ($this->outputFileName !== '') {
+            unlink($this->outputFileName);
+            $this->outputFileName = '';
+        }
+    }
+
+    /**
+     * @dataProvider providerScatterCharts
+     */
+    public function testBezierCount(int $expectedCount, string $inputFile): void
+    {
+        $file = self::DIRECTORY . $inputFile;
+        $reader = new XlsxReader();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($file);
+
+        $writer = new XlsxWriter($spreadsheet);
+        $writer->setIncludeCharts(true);
+        $this->outputFileName = File::temporaryFilename();
+        $writer->save($this->outputFileName);
+        $spreadsheet->disconnectWorksheets();
+
+        $file = 'zip://';
+        $file .= $this->outputFileName;
+        $file .= '#xl/charts/chart2.xml';
+        $data = file_get_contents($file);
+        // confirm that file contains expected tags
+        if ($data === false) {
+            self::fail('Unable to read file');
+        } else {
+            self::assertSame(1, substr_count($data, '<c:scatterStyle val='));
+            self::assertSame($expectedCount ? 1 : 0, substr_count($data, '<c:scatterStyle val="smoothMarker"/>'));
+            self::assertSame($expectedCount, substr_count($data, '<c:smooth val="1"/>'));
+        }
+    }
+
+    public function providerScatterCharts(): array
+    {
+        return [
+            'no line' => [0, '32readwriteScatterChart1.xlsx'],
+            'smooth line (Bezier)' => [3, '32readwriteScatterChart2.xlsx'],
+            'straight line' => [0, '32readwriteScatterChart3.xlsx'],
+        ];
+    }
+
+    public function testAreaPercentageNoCat(): void
+    {
+        $file = self::DIRECTORY . '32readwriteAreaPercentageChart1.xlsx';
+        $reader = new XlsxReader();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($file);
+
+        $writer = new XlsxWriter($spreadsheet);
+        $writer->setIncludeCharts(true);
+        $this->outputFileName = File::temporaryFilename();
+        $writer->save($this->outputFileName);
+        $spreadsheet->disconnectWorksheets();
+
+        $file = 'zip://';
+        $file .= $this->outputFileName;
+        $file .= '#xl/charts/chart1.xml';
+        $data = file_get_contents($file);
+        // confirm that file contains expected tags
+        if ($data === false) {
+            self::fail('Unable to read file');
+        } else {
+            self::assertSame(0, substr_count($data, '<c:cat>'));
+        }
+    }
+}