Charts Support for Rounded Corners and Trendlines (#2976)

Fix #2968. Fix #2815. Solution largely based on suggestions by @bridgeplayr.

samples/Chart/33_Chart_create_scatter5_trendlines.php

@@ -0,0 +1,273 @@
+<?php
+
+use PhpOffice\PhpSpreadsheet\Chart\Axis;
+use PhpOffice\PhpSpreadsheet\Chart\Chart;
+use PhpOffice\PhpSpreadsheet\Chart\ChartColor;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeries;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeriesValues;
+use PhpOffice\PhpSpreadsheet\Chart\Legend as ChartLegend;
+use PhpOffice\PhpSpreadsheet\Chart\PlotArea;
+use PhpOffice\PhpSpreadsheet\Chart\Properties;
+use PhpOffice\PhpSpreadsheet\Chart\Title;
+use PhpOffice\PhpSpreadsheet\Chart\TrendLine;
+use PhpOffice\PhpSpreadsheet\IOFactory;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+
+require __DIR__ . '/../Header.php';
+
+$spreadsheet = new Spreadsheet();
+$dataSheet = $spreadsheet->getActiveSheet();
+$dataSheet->setTitle('Data');
+// changed data to simulate a trend chart - Xaxis are dates; Yaxis are 3 meausurements from each date
+$dataSheet->fromArray(
+    [
+        ['', 'metric1', 'metric2', 'metric3'],
+        ['=DATEVALUE("2021-01-01")', 12.1, 15.1, 21.1],
+        ['=DATEVALUE("2021-04-01")', 56.2, 73.2, 86.2],
+        ['=DATEVALUE("2021-07-01")', 52.2, 61.2, 69.2],
+        ['=DATEVALUE("2021-10-01")', 30.2, 22.2, 0.2],
+        ['=DATEVALUE("2022-01-01")', 40.1, 38.1, 65.1],
+        ['=DATEVALUE("2022-04-01")', 45.2, 44.2, 96.2],
+        ['=DATEVALUE("2022-07-01")', 52.2, 51.2, 55.2],
+        ['=DATEVALUE("2022-10-01")', 41.2, 72.2, 56.2],
+    ]
+);
+
+$dataSheet->getStyle('A2:A9')->getNumberFormat()->setFormatCode(Properties::FORMAT_CODE_DATE_ISO8601);
+$dataSheet->getColumnDimension('A')->setAutoSize(true);
+$dataSheet->setSelectedCells('A1');
+
+// Set the Labels for each data series we want to plot
+//     Datatype
+//     Cell reference for data
+//     Format Code
+//     Number of datapoints in series
+$dataSeriesLabels = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Data!$B$1', null, 1),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Data!$C$1', null, 1),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Data!$D$1', null, 1),
+];
+// Set the X-Axis Labels
+// NUMBER, not STRING
+// added x-axis values for each of the 3 metrics
+// added FORMATE_CODE_NUMBER
+// Number of datapoints in series
+$xAxisTickValues = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$A$2:$A$9', Properties::FORMAT_CODE_DATE_ISO8601, 8),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$A$2:$A$9', Properties::FORMAT_CODE_DATE_ISO8601, 8),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$A$2:$A$9', Properties::FORMAT_CODE_DATE_ISO8601, 8),
+];
+// Set the Data values for each data series we want to plot
+//     Datatype
+//     Cell reference for data
+//     Format Code
+//     Number of datapoints in series
+//     Data values
+//     Data Marker
+//     Data Marker Color fill/[fill,Border]
+//     Data Marker size
+//   Color(s) added
+// added FORMAT_CODE_NUMBER
+$dataSeriesValues = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$B$2:$B$9', Properties::FORMAT_CODE_NUMBER, 8, null, 'diamond', null, 5),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$C$2:$C$9', Properties::FORMAT_CODE_NUMBER, 8, null, 'square', '*accent1', 6),
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$D$2:$D$9', Properties::FORMAT_CODE_NUMBER, 8, null, null, null, 7), // let Excel choose marker shape
+];
+// series 1 - metric1
+// marker details
+$dataSeriesValues[0]
+    ->getMarkerFillColor()
+    ->setColorProperties('0070C0', null, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+$dataSeriesValues[0]
+    ->getMarkerBorderColor()
+    ->setColorProperties('002060', null, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+
+// line details - dashed, smooth line (Bezier) with arrows, 40% transparent
+$dataSeriesValues[0]
+    ->setSmoothLine(true)
+    ->setScatterLines(true)
+    ->setLineColorProperties('accent1', 40, ChartColor::EXCEL_COLOR_TYPE_SCHEME); // value, alpha, type
+$dataSeriesValues[0]->setLineStyleProperties(
+    2.5, // width in points
+    Properties::LINE_STYLE_COMPOUND_TRIPLE, // compound
+    Properties::LINE_STYLE_DASH_SQUARE_DOT, // dash
+    Properties::LINE_STYLE_CAP_SQUARE, // cap
+    Properties::LINE_STYLE_JOIN_MITER, // join
+    Properties::LINE_STYLE_ARROW_TYPE_OPEN, // head type
+    Properties::LINE_STYLE_ARROW_SIZE_4, // head size preset index
+    Properties::LINE_STYLE_ARROW_TYPE_ARROW, // end type
+    Properties::LINE_STYLE_ARROW_SIZE_6 // end size preset index
+);
+
+// series 2 - metric2, straight line - no special effects, connected
+$dataSeriesValues[1] // square marker border color
+    ->getMarkerBorderColor()
+    ->setColorProperties('accent6', 3, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+$dataSeriesValues[1] // square marker fill color
+    ->getMarkerFillColor()
+    ->setColorProperties('0FFF00', null, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+$dataSeriesValues[1]
+    ->setScatterLines(true)
+    ->setSmoothLine(false)
+    ->setLineColorProperties('FF0000', 80, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+$dataSeriesValues[1]->setLineWidth(2.0);
+
+// series 3 - metric3, markers, no line
+$dataSeriesValues[2] // triangle? fill
+    //->setPointMarker('triangle') // let Excel choose shape, which is predicted to be a triangle
+    ->getMarkerFillColor()
+    ->setColorProperties('FFFF00', null, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+$dataSeriesValues[2] // triangle border
+    ->getMarkerBorderColor()
+    ->setColorProperties('accent4', null, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+$dataSeriesValues[2]->setScatterLines(false); // points not connected
+  // Added so that Xaxis shows dates instead of Excel-equivalent-year1900-numbers
+$xAxis = new Axis();
+$xAxis->setAxisNumberProperties(Properties::FORMAT_CODE_DATE_ISO8601, true);
+
+// Build the dataseries
+$series = new DataSeries(
+    DataSeries::TYPE_SCATTERCHART, // plotType
+    null, // plotGrouping (Scatter charts don't have grouping)
+    range(0, count($dataSeriesValues) - 1), // plotOrder
+    $dataSeriesLabels, // plotLabel
+    $xAxisTickValues, // plotCategory
+    $dataSeriesValues, // plotValues
+    null, // plotDirection
+    null, // smooth line
+    DataSeries::STYLE_SMOOTHMARKER // plotStyle
+);
+
+// Set the series in the plot area
+$plotArea = new PlotArea(null, [$series]);
+// Set the chart legend
+$legend = new ChartLegend(ChartLegend::POSITION_TOPRIGHT, null, false);
+
+$title = new Title('Test Scatter Chart');
+$yAxisLabel = new Title('Value ($k)');
+
+// Create the chart
+$chart = new Chart(
+    'chart1', // name
+    $title, // title
+    $legend, // legend
+    $plotArea, // plotArea
+    true, // plotVisibleOnly
+    DataSeries::EMPTY_AS_GAP, // displayBlanksAs
+    null, // xAxisLabel
+    $yAxisLabel,  // yAxisLabel
+    // added xAxis for correct date display
+    $xAxis, // xAxis
+    //  $yAxis, // yAxis
+);
+
+// Set the position of the chart in the chart sheet
+$chart->setTopLeftPosition('A1');
+$chart->setBottomRightPosition('P12');
+
+// create a 'Chart' worksheet, add $chart to it
+$spreadsheet->createSheet();
+$chartSheet = $spreadsheet->getSheet(1);
+$chartSheet->setTitle('Scatter Chart');
+
+$chartSheet = $spreadsheet->getSheetByName('Scatter Chart');
+// Add the chart to the worksheet
+$chartSheet->addChart($chart);
+
+// ------------ Demonstrate Trendlines for metric3 values in a new chart ------------
+
+$dataSeriesLabels = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, 'Data!$D$1', null, 1),
+];
+$xAxisTickValues = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$A$2:$A$9', Properties::FORMAT_CODE_DATE_ISO8601, 8),
+];
+
+$dataSeriesValues = [
+    new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, 'Data!$D$2:$D$9', Properties::FORMAT_CODE_NUMBER, 4, null, 'triangle', null, 7),
+];
+
+// add 3 trendlines:
+// 1- linear, double-ended arrow, w=0.5, same color as marker fill; nodispRSqr, nodispEq
+// 2- polynomial (order=3) no-arrow trendline, w=1.25, same color as marker fill; dispRSqr, dispEq
+// 3- moving Avg (period=2) single-arrow trendline, w=1.5, same color as marker fill; no dispRSqr, no dispEq
+$trendLines = [
+    new TrendLine(TrendLine::TRENDLINE_LINEAR, null, null, false, false),
+    new TrendLine(TrendLine::TRENDLINE_POLYNOMIAL, 3, null, true, true),
+    new TrendLine(TrendLine::TRENDLINE_MOVING_AVG, null, 2, true),
+];
+$dataSeriesValues[0]->setTrendLines($trendLines);
+
+// Suppress connecting lines; instead, add different Trendline algorithms to
+// determine how well the data fits the algorithm (Rsquared="goodness of fit")
+// Display RSqr plus the eqn just because we can.
+
+$dataSeriesValues[0]->setScatterLines(false); // points not connected
+$dataSeriesValues[0]->getMarkerFillColor()
+    ->setColorProperties('FFFF00', null, ChartColor::EXCEL_COLOR_TYPE_ARGB);
+$dataSeriesValues[0]->getMarkerBorderColor()
+    ->setColorProperties('accent4', null, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+
+// add properties to the trendLines - give each a different color
+$dataSeriesValues[0]->getTrendLines()[0]->getLineColor()->setColorProperties('accent4', null, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+$dataSeriesValues[0]->getTrendLines()[0]->setLineStyleProperties(0.5, null, null, null, null, Properties::LINE_STYLE_ARROW_TYPE_STEALTH, 5, Properties::LINE_STYLE_ARROW_TYPE_OPEN, 8);
+
+$dataSeriesValues[0]->getTrendLines()[1]->getLineColor()->setColorProperties('accent3', null, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+$dataSeriesValues[0]->getTrendLines()[1]->setLineStyleProperties(1.25);
+
+$dataSeriesValues[0]->getTrendLines()[2]->getLineColor()->setColorProperties('accent2', null, ChartColor::EXCEL_COLOR_TYPE_SCHEME);
+$dataSeriesValues[0]->getTrendLines()[2]->setLineStyleProperties(1.5, null, null, null, null, null, null, Properties::LINE_STYLE_ARROW_TYPE_OPEN, 8);
+
+$xAxis = new Axis();
+$xAxis->setAxisNumberProperties(Properties::FORMAT_CODE_DATE_ISO8601); // m/d/yyyy
+
+// Build the dataseries
+$series = new DataSeries(
+    DataSeries::TYPE_SCATTERCHART, // plotType
+    null, // plotGrouping (Scatter charts don't have grouping)
+    range(0, count($dataSeriesValues) - 1), // plotOrder
+    $dataSeriesLabels, // plotLabel
+    $xAxisTickValues, // plotCategory
+    $dataSeriesValues, // plotValues
+    null, // plotDirection
+    null, // smooth line
+    DataSeries::STYLE_SMOOTHMARKER // plotStyle
+);
+
+// Set the series in the plot area
+$plotArea = new PlotArea(null, [$series]);
+// Set the chart legend
+$legend = new ChartLegend(ChartLegend::POSITION_TOPRIGHT, null, false);
+
+$title = new Title('Test Scatter Chart - trendlines for metric3 values');
+$yAxisLabel = new Title('Value ($k)');
+
+// Create the chart
+$chart = new Chart(
+    'chart2', // name
+    $title, // title
+    $legend, // legend
+    $plotArea, // plotArea
+    true, // plotVisibleOnly
+    DataSeries::EMPTY_AS_GAP, // displayBlanksAs
+    null, // xAxisLabel
+    $yAxisLabel,  // yAxisLabel
+    // added xAxis for correct date display
+    $xAxis, // xAxis
+    //  $yAxis, // yAxis
+);
+
+// Set the position of the chart in the chart sheet below the first chart
+$chart->setTopLeftPosition('A13');
+$chart->setBottomRightPosition('P25');
+
+// Add the chart to the worksheet $chartSheet
+$chartSheet->addChart($chart);
+
+// Save Excel 2007 file
+$filename = $helper->getFilename(__FILE__);
+$writer = IOFactory::createWriter($spreadsheet, 'Xlsx');
+$writer->setIncludeCharts(true);
+$callStartTime = microtime(true);
+$writer->save($filename);
+$helper->logWrite($writer, $filename, $callStartTime);

src/PhpSpreadsheet/Chart/Chart.php

@@ -147,6 +147,9 @@ class Chart
     /** @var bool */
     private $noFill = false;
 
+    /** @var bool */
+    private $roundedCorners = false;
+
     /**
      * Create a new Chart.
      * majorGridlines and minorGridlines are deprecated, moved to Axis.
@@ -762,4 +765,16 @@ class Chart
 
         return $this;
     }
+
+    public function getRoundedCorners(): bool
+    {
+        return $this->roundedCorners;
+    }
+
+    public function setRoundedCorners(bool $roundedCorners): self
+    {
+        $this->roundedCorners = $roundedCorners;
+
+        return $this;
+    }
 }

src/PhpSpreadsheet/Chart/DataSeriesValues.php

@@ -88,6 +88,9 @@ class DataSeriesValues extends Properties
     /** @var ?Layout */
     private $labelLayout;
 
+    /** @var TrendLine[] */
+    private $trendLines = [];
+
     /**
      * Create a new DataSeriesValues object.
      *
@@ -577,4 +580,16 @@ class DataSeriesValues extends Properties
 
         return $this;
     }
+
+    public function setTrendLines(array $trendLines): self
+    {
+        $this->trendLines = $trendLines;
+
+        return $this;
+    }
+
+    public function getTrendLines(): array
+    {
+        return $this->trendLines;
+    }
 }

src/PhpSpreadsheet/Chart/TrendLine.php

@@ -0,0 +1,126 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Chart;
+
+class TrendLine extends Properties
+{
+    const TRENDLINE_EXPONENTIAL = 'exp';
+    const TRENDLINE_LINEAR = 'linear';
+    const TRENDLINE_LOGARITHMIC = 'log';
+    const TRENDLINE_POLYNOMIAL = 'poly'; // + 'order'
+    const TRENDLINE_POWER = 'power';
+    const TRENDLINE_MOVING_AVG = 'movingAvg'; // + 'period'
+    const TRENDLINE_TYPES = [
+        self::TRENDLINE_EXPONENTIAL,
+        self::TRENDLINE_LINEAR,
+        self::TRENDLINE_LOGARITHMIC,
+        self::TRENDLINE_POLYNOMIAL,
+        self::TRENDLINE_POWER,
+        self::TRENDLINE_MOVING_AVG,
+    ];
+
+    /** @var string */
+    private $trendLineType = 'linear'; // TRENDLINE_LINEAR
+
+    /** @var int */
+    private $order = 2;
+
+    /** @var int */
+    private $period = 3;
+
+    /** @var bool */
+    private $dispRSqr = false;
+
+    /** @var bool */
+    private $dispEq = false;
+
+    /**
+     * Create a new TrendLine object.
+     */
+    public function __construct(string $trendLineType = '', ?int $order = null, ?int $period = null, bool $dispRSqr = false, bool $dispEq = false)
+    {
+        parent::__construct();
+        $this->setTrendLineProperties($trendLineType, $order, $period, $dispRSqr, $dispEq);
+    }
+
+    public function getTrendLineType(): string
+    {
+        return $this->trendLineType;
+    }
+
+    public function setTrendLineType(string $trendLineType): self
+    {
+        $this->trendLineType = $trendLineType;
+
+        return $this;
+    }
+
+    public function getOrder(): int
+    {
+        return $this->order;
+    }
+
+    public function setOrder(int $order): self
+    {
+        $this->order = $order;
+
+        return $this;
+    }
+
+    public function getPeriod(): int
+    {
+        return $this->period;
+    }
+
+    public function setPeriod(int $period): self
+    {
+        $this->period = $period;
+
+        return $this;
+    }
+
+    public function getDispRSqr(): bool
+    {
+        return $this->dispRSqr;
+    }
+
+    public function setDispRSqr(bool $dispRSqr): self
+    {
+        $this->dispRSqr = $dispRSqr;
+
+        return $this;
+    }
+
+    public function getDispEq(): bool
+    {
+        return $this->dispEq;
+    }
+
+    public function setDispEq(bool $dispEq): self
+    {
+        $this->dispEq = $dispEq;
+
+        return $this;
+    }
+
+    public function setTrendLineProperties(?string $trendLineType = null, ?int $order = 0, ?int $period = 0, ?bool $dispRSqr = false, ?bool $dispEq = false): self
+    {
+        if (!empty($trendLineType)) {
+            $this->setTrendLineType($trendLineType);
+        }
+        if ($order !== null) {
+            $this->setOrder($order);
+        }
+        if ($period !== null) {
+            $this->setPeriod($period);
+        }
+        if ($dispRSqr !== null) {
+            $this->setDispRSqr($dispRSqr);
+        }
+        if ($dispEq !== null) {
+            $this->setDispEq($dispEq);
+        }
+
+        return $this;
+    }
+}

src/PhpSpreadsheet/Reader/Xlsx/Chart.php

@@ -13,6 +13,7 @@ use PhpOffice\PhpSpreadsheet\Chart\Legend;
 use PhpOffice\PhpSpreadsheet\Chart\PlotArea;
 use PhpOffice\PhpSpreadsheet\Chart\Properties;
 use PhpOffice\PhpSpreadsheet\Chart\Title;
+use PhpOffice\PhpSpreadsheet\Chart\TrendLine;
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
 use PhpOffice\PhpSpreadsheet\Style\Font;
 use SimpleXMLElement;
@@ -76,6 +77,7 @@ class Chart
         $chartNoFill = false;
         $gradientArray = [];
         $gradientLin = null;
+        $roundedCorners = false;
         foreach ($chartElementsC as $chartElementKey => $chartElement) {
             switch ($chartElementKey) {
                 case 'spPr':
@@ -84,6 +86,11 @@ class Chart
                         $chartNoFill = true;
                     }
 
+                    break;
+                case 'roundedCorners':
+                    /** @var bool */
+                    $roundedCorners = self::getAttribute($chartElementsC->roundedCorners, 'val', 'boolean');
+
                     break;
                 case 'chart':
                     foreach ($chartElement as $chartDetailsKey => $chartDetails) {
@@ -370,6 +377,7 @@ class Chart
         if ($chartNoFill) {
             $chart->setNoFill(true);
         }
+        $chart->setRoundedCorners($roundedCorners);
         if (is_bool($autoTitleDeleted)) {
             $chart->setAutoTitleDeleted($autoTitleDeleted);
         }
@@ -466,6 +474,7 @@ class Chart
                     $markerBorderColor = null;
                     $lineStyle = null;
                     $labelLayout = null;
+                    $trendLines = [];
                     foreach ($seriesDetails as $seriesKey => $seriesDetail) {
                         switch ($seriesKey) {
                             case 'idx':
@@ -513,6 +522,23 @@ class Chart
                                     }
                                 }
 
+                                break;
+                            case 'trendline':
+                                $trendLine = new TrendLine();
+                                $this->readLineStyle($seriesDetail, $trendLine);
+                                /** @var ?string */
+                                $trendLineType = self::getAttribute($seriesDetail->trendlineType, 'val', 'string');
+                                /** @var ?bool */
+                                $dispRSqr = self::getAttribute($seriesDetail->dispRSqr, 'val', 'boolean');
+                                /** @var ?bool */
+                                $dispEq = self::getAttribute($seriesDetail->dispEq, 'val', 'boolean');
+                                /** @var ?int */
+                                $order = self::getAttribute($seriesDetail->order, 'val', 'integer');
+                                /** @var ?int */
+                                $period = self::getAttribute($seriesDetail->period, 'val', 'integer');
+                                $trendLine->setTrendLineProperties($trendLineType, $order, $period, $dispRSqr, $dispEq);
+                                $trendLines[] = $trendLine;
+
                                 break;
                             case 'marker':
                                 $marker = self::getAttribute($seriesDetail->symbol, 'val', 'string');
@@ -651,6 +677,17 @@ class Chart
                             $seriesValues[$seriesIndex]->setSmoothLine(true);
                         }
                     }
+                    if (!empty($trendLines)) {
+                        if (isset($seriesLabel[$seriesIndex])) {
+                            $seriesLabel[$seriesIndex]->setTrendLines($trendLines);
+                        }
+                        if (isset($seriesCategory[$seriesIndex])) {
+                            $seriesCategory[$seriesIndex]->setTrendLines($trendLines);
+                        }
+                        if (isset($seriesValues[$seriesIndex])) {
+                            $seriesValues[$seriesIndex]->setTrendLines($trendLines);
+                        }
+                    }
             }
         }
         /** @phpstan-ignore-next-line */

src/PhpSpreadsheet/Writer/Xlsx/Chart.php

@@ -11,6 +11,7 @@ use PhpOffice\PhpSpreadsheet\Chart\Legend;
 use PhpOffice\PhpSpreadsheet\Chart\PlotArea;
 use PhpOffice\PhpSpreadsheet\Chart\Properties;
 use PhpOffice\PhpSpreadsheet\Chart\Title;
+use PhpOffice\PhpSpreadsheet\Chart\TrendLine;
 use PhpOffice\PhpSpreadsheet\Shared\XMLWriter;
 use PhpOffice\PhpSpreadsheet\Writer\Exception as WriterException;
 
@@ -58,7 +59,7 @@ class Chart extends WriterPart
         $objWriter->writeAttribute('val', 'en-GB');
         $objWriter->endElement();
         $objWriter->startElement('c:roundedCorners');
-        $objWriter->writeAttribute('val', '0');
+        $objWriter->writeAttribute('val', $chart->getRoundedCorners() ? '1' : '0');
         $objWriter->endElement();
 
         $this->writeAlternateContent($objWriter);
@@ -1123,6 +1124,65 @@ class Chart extends WriterPart
                 $objWriter->writeAttribute('val', '0');
                 $objWriter->endElement();
             }
+            // Trendlines
+            if ($plotSeriesValues !== false) {
+                foreach ($plotSeriesValues->getTrendLines() as $trendLine) {
+                    $trendLineType = $trendLine->getTrendLineType();
+                    $order = $trendLine->getOrder();
+                    $period = $trendLine->getPeriod();
+                    $dispRSqr = $trendLine->getDispRSqr();
+                    $dispEq = $trendLine->getDispEq();
+                    $trendLineColor = $trendLine->getLineColor(); // ChartColor
+                    $trendLineWidth = $trendLine->getLineStyleProperty('width');
+
+                    $objWriter->startElement('c:trendline'); // N.B. lowercase 'ell'
+                    $objWriter->startElement('c:spPr');
+
+                    if (!$trendLineColor->isUsable()) {
+                        // use dataSeriesValues line color as a backup if $trendLineColor is null
+                        $dsvLineColor = $plotSeriesValues->getLineColor();
+                        if ($dsvLineColor->isUsable()) {
+                            $trendLine
+                                ->getLineColor()
+                                ->setColorProperties($dsvLineColor->getValue(), $dsvLineColor->getAlpha(), $dsvLineColor->getType());
+                        }
+                    } // otherwise, hope Excel does the right thing
+
+                    $this->writeLineStyles($objWriter, $trendLine, false); // suppress noFill
+
+                    $objWriter->endElement(); // spPr
+
+                    $objWriter->startElement('c:trendlineType'); // N.B lowercase 'ell'
+                    $objWriter->writeAttribute('val', $trendLineType);
+                    $objWriter->endElement(); // trendlineType
+                    if ($trendLineType == TrendLine::TRENDLINE_POLYNOMIAL) {
+                        $objWriter->startElement('c:order');
+                        $objWriter->writeAttribute('val', $order);
+                        $objWriter->endElement(); // order
+                    }
+                    if ($trendLineType == TrendLine::TRENDLINE_MOVING_AVG) {
+                        $objWriter->startElement('c:period');
+                        $objWriter->writeAttribute('val', $period);
+                        $objWriter->endElement(); // period
+                    }
+                    $objWriter->startElement('c:dispRSqr');
+                    $objWriter->writeAttribute('val', $dispRSqr ? '1' : '0');
+                    $objWriter->endElement();
+                    $objWriter->startElement('c:dispEq');
+                    $objWriter->writeAttribute('val', $dispEq ? '1' : '0');
+                    $objWriter->endElement();
+                    if ($groupType === DataSeries::TYPE_SCATTERCHART || $groupType === DataSeries::TYPE_LINECHART) {
+                        $objWriter->startElement('c:trendlineLbl');
+                        $objWriter->startElement('c:numFmt');
+                        $objWriter->writeAttribute('formatCode', 'General');
+                        $objWriter->writeAttribute('sourceLinked', '0');
+                        $objWriter->endElement();  // numFmt
+                        $objWriter->endElement();  // trendlineLbl
+                    }
+
+                    $objWriter->endElement(); // trendline
+                }
+            }
 
             //    Category Labels
             $plotSeriesCategory = $plotGroup->getPlotCategoryByIndex($plotSeriesIdx);

tests/PhpSpreadsheetTests/Chart/RoundedCornersTest.php

@@ -0,0 +1,74 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Chart;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx as XlsxWriter;
+use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
+
+class RoundedCornersTest extends AbstractFunctional
+{
+    private const DIRECTORY = 'samples' . DIRECTORY_SEPARATOR . 'templates' . DIRECTORY_SEPARATOR;
+
+    public function readCharts(XlsxReader $reader): void
+    {
+        $reader->setIncludeCharts(true);
+    }
+
+    public function writeCharts(XlsxWriter $writer): void
+    {
+        $writer->setIncludeCharts(true);
+    }
+
+    public function testRounded(): void
+    {
+        $file = self::DIRECTORY . '32readwriteAreaChart1.xlsx';
+        $reader = new XlsxReader();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($file);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::assertSame(1, $sheet->getChartCount());
+        /** @var callable */
+        $callableReader = [$this, 'readCharts'];
+        /** @var callable */
+        $callableWriter = [$this, 'writeCharts'];
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, 'Xlsx', $callableReader, $callableWriter);
+        $spreadsheet->disconnectWorksheets();
+
+        $sheet = $reloadedSpreadsheet->getActiveSheet();
+        self::assertSame('Data', $sheet->getTitle());
+        $charts = $sheet->getChartCollection();
+        self::assertCount(1, $charts);
+        $chart = $charts[0];
+        self::assertNotNull($chart);
+        self::assertTrue($chart->getRoundedCorners());
+
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+
+    public function testNotRounded(): void
+    {
+        $file = self::DIRECTORY . '32readwriteAreaChart2.xlsx';
+        $reader = new XlsxReader();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($file);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::assertSame(1, $sheet->getChartCount());
+        /** @var callable */
+        $callableReader = [$this, 'readCharts'];
+        /** @var callable */
+        $callableWriter = [$this, 'writeCharts'];
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, 'Xlsx', $callableReader, $callableWriter);
+        $spreadsheet->disconnectWorksheets();
+
+        $sheet = $reloadedSpreadsheet->getActiveSheet();
+        self::assertSame('Data', $sheet->getTitle());
+        $charts = $sheet->getChartCollection();
+        self::assertCount(1, $charts);
+        $chart = $charts[0];
+        self::assertNotNull($chart);
+        self::assertFalse($chart->getRoundedCorners());
+
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+}

tests/PhpSpreadsheetTests/Chart/TrendLineTest.php

@@ -0,0 +1,97 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Chart;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx as XlsxWriter;
+use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
+
+class TrendLineTest extends AbstractFunctional
+{
+    private const DIRECTORY = 'samples' . DIRECTORY_SEPARATOR . 'templates' . DIRECTORY_SEPARATOR;
+
+    public function readCharts(XlsxReader $reader): void
+    {
+        $reader->setIncludeCharts(true);
+    }
+
+    public function writeCharts(XlsxWriter $writer): void
+    {
+        $writer->setIncludeCharts(true);
+    }
+
+    public function testTrendLine(): void
+    {
+        $file = self::DIRECTORY . '32readwriteScatterChartTrendlines1.xlsx';
+        $reader = new XlsxReader();
+        $reader->setIncludeCharts(true);
+        $spreadsheet = $reader->load($file);
+        $sheet = $spreadsheet->getSheet(1);
+        self::assertSame(2, $sheet->getChartCount());
+        /** @var callable */
+        $callableReader = [$this, 'readCharts'];
+        /** @var callable */
+        $callableWriter = [$this, 'writeCharts'];
+        $reloadedSpreadsheet = $this->writeAndReload($spreadsheet, 'Xlsx', $callableReader, $callableWriter);
+        $spreadsheet->disconnectWorksheets();
+
+        $sheet = $reloadedSpreadsheet->getSheet(1);
+        self::assertSame('Scatter Chart', $sheet->getTitle());
+        $charts = $sheet->getChartCollection();
+        self::assertCount(2, $charts);
+
+        $chart = $charts[0];
+        self::assertNotNull($chart);
+        $plotArea = $chart->getPlotArea();
+        self::assertNotNull($plotArea);
+        $plotSeriesArray = $plotArea->getPlotGroup();
+        self::assertCount(1, $plotSeriesArray);
+        $plotSeries = $plotSeriesArray[0];
+        $valuesArray = $plotSeries->getPlotValues();
+        self::assertCount(3, $valuesArray);
+        self::assertEmpty($valuesArray[0]->getTrendLines());
+        self::assertEmpty($valuesArray[1]->getTrendLines());
+        self::assertEmpty($valuesArray[2]->getTrendLines());
+
+        $chart = $charts[1];
+        self::assertNotNull($chart);
+        $plotArea = $chart->getPlotArea();
+        self::assertNotNull($plotArea);
+        $plotSeriesArray = $plotArea->getPlotGroup();
+        self::assertCount(1, $plotSeriesArray);
+        $plotSeries = $plotSeriesArray[0];
+        $valuesArray = $plotSeries->getPlotValues();
+        self::assertCount(1, $valuesArray);
+        $trendLines = $valuesArray[0]->getTrendLines();
+        self::assertCount(3, $trendLines);
+
+        $trendLine = $trendLines[0];
+        self::assertSame('linear', $trendLine->getTrendLineType());
+        self::assertFalse($trendLine->getDispRSqr());
+        self::assertFalse($trendLine->getDispEq());
+        $lineColor = $trendLine->getLineColor();
+        self::assertSame('accent4', $lineColor->getValue());
+        self::assertSame('stealth', $trendLine->getLineStyleProperty(['arrow', 'head', 'type']));
+        self::assertEquals(0.5, $trendLine->getLineStyleProperty('width'));
+
+        $trendLine = $trendLines[1];
+        self::assertSame('poly', $trendLine->getTrendLineType());
+        self::assertTrue($trendLine->getDispRSqr());
+        self::assertTrue($trendLine->getDispEq());
+        $lineColor = $trendLine->getLineColor();
+        self::assertSame('accent3', $lineColor->getValue());
+        self::assertNull($trendLine->getLineStyleProperty(['arrow', 'head', 'type']));
+        self::assertEquals(1.25, $trendLine->getLineStyleProperty('width'));
+
+        $trendLine = $trendLines[2];
+        self::assertSame('movingAvg', $trendLine->getTrendLineType());
+        self::assertTrue($trendLine->getDispRSqr());
+        self::assertFalse($trendLine->getDispEq());
+        $lineColor = $trendLine->getLineColor();
+        self::assertSame('accent2', $lineColor->getValue());
+        self::assertNull($trendLine->getLineStyleProperty(['arrow', 'head', 'type']));
+        self::assertEquals(1.5, $trendLine->getLineStyleProperty('width'));
+
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+}