This closes #2169, support to set font for chart legends (#2171)

- Add Font field in the ChartLegend data type
- Add Legend field in the ChartSeries data type
- Update documentation for legend font support
- Update unit tests

Author: Copilot

chart.go

@@ -765,6 +765,7 @@ func (opts *Chart) parseTitle() {
 //	Categories
 //	Values
 //	Fill
+//	Legend
 //	Line
 //	Marker
 //	DataLabel
@@ -787,7 +788,10 @@ func (opts *Chart) parseTitle() {
 // optional and the default value was same with 'Values'.
 //
 // Fill: This set the format for the data series fill. The 'Fill' property is
-// optional
+// optional.
+//
+// Legend: This set the font of legend text for a data series. The 'Legend'
+// property is optional.
 //
 // Line: This sets the line format of the line chart. The 'Line' property is
 // optional and if it isn't supplied it will default style. The options that
@@ -819,6 +823,7 @@ func (opts *Chart) parseTitle() {
 //
 //	Position
 //	ShowLegendKey
+//	Font
 //
 // Position: Set the position of the chart legend. The default legend position
 // is bottom. The available positions are:
@@ -833,6 +838,11 @@ func (opts *Chart) parseTitle() {
 // ShowLegendKey: Set the legend keys shall be shown in data labels. The default
 // value is false.
 //
+// Font: Set the font properties of the chart legend text. The properties that
+// can be set are the same as the font object that is used for cell formatting.
+// The font family, size, color, bold, italic, underline, and strike properties
+// can be set.
+//
 // Set properties of the chart title. The properties that can be set are:
 //
 //	Title
@@ -1008,6 +1018,9 @@ func (opts *Chart) parseTitle() {
 // Set chart size by 'Dimension' property. The 'Dimension' property is optional.
 // The default width is 480, and height is 260.
 //
+// Set chart legend for all data series by 'Legend' property. The 'Legend'
+// property is optional.
+//
 // Set the bubble size in all data series for the bubble chart or 3D bubble
 // chart by 'BubbleSizes' property. The 'BubbleSizes' property is optional. The
 // default width is 100, and the value should be great than 0 and less or equal

chart_test.go

@@ -171,6 +171,7 @@ func TestAddChart(t *testing.T) {
 					Width: 1,
 				},
 			},
+			Legend: ChartLegend{Font: &Font{Family: "Arial", Size: 11, Strike: true, Color: "777777"}},
 		},
 	}
 	series2 := []ChartSeries{
@@ -225,7 +226,7 @@ func TestAddChart(t *testing.T) {
 		{sheetName: "Sheet1", cell: "P1", opts: &Chart{Type: Col, Series: series, Format: format, Legend: ChartLegend{Position: "none", ShowLegendKey: true}, Title: []RichTextRun{{Text: "2D Column Chart", Font: &Font{Size: 11, Family: "Calibri"}}}, PlotArea: plotArea, Border: ChartLine{Type: ChartLineNone}, ShowBlanksAs: "zero", XAxis: ChartAxis{Font: Font{Bold: true, Italic: true, Underline: "dbl", Family: "Times New Roman", Size: 15, Strike: true, Color: "000000"}, Title: []RichTextRun{{Text: "Primary Horizontal Axis Title"}}}, YAxis: ChartAxis{Font: Font{Bold: false, Italic: false, Underline: "sng", Color: "777777"}, Title: []RichTextRun{{Text: "Primary Vertical Axis Title", Font: &Font{Color: "777777", Bold: true, Italic: true, Size: 12}}}}}},
 		{sheetName: "Sheet1", cell: "X1", opts: &Chart{Type: ColStacked, Series: series, Format: format, Legend: legend, Title: []RichTextRun{{Text: "2D Stacked Column Chart"}}, PlotArea: plotArea, Fill: Fill{Type: "pattern", Pattern: 1}, Border: ChartLine{Type: ChartLineAutomatic}, ShowBlanksAs: "zero", GapWidth: uintPtr(10), Overlap: intPtr(100)}},
 		{sheetName: "Sheet1", cell: "P16", opts: &Chart{Type: ColPercentStacked, Series: series, Format: format, Legend: legend, Title: []RichTextRun{{Text: "100% Stacked Column Chart"}}, PlotArea: plotArea, Fill: Fill{Type: "pattern", Color: []string{"EEEEEE"}, Pattern: 1}, Border: ChartLine{Type: ChartLineSolid, Width: 2}, ShowBlanksAs: "zero", XAxis: ChartAxis{Alignment: Alignment{Vertical: "wordArtVertRtl", TextRotation: 0}}}},
-		{sheetName: "Sheet1", cell: "X16", opts: &Chart{Type: Col3DClustered, Series: series, Format: format, Legend: ChartLegend{Position: "bottom", ShowLegendKey: false}, Title: []RichTextRun{{Text: "3D Clustered Column Chart"}}, PlotArea: plotArea, ShowBlanksAs: "zero"}},
+		{sheetName: "Sheet1", cell: "X16", opts: &Chart{Type: Col3DClustered, Series: series, Format: format, Legend: ChartLegend{Position: "bottom", ShowLegendKey: false, Font: &Font{Size: 10}}, Title: []RichTextRun{{Text: "3D Clustered Column Chart"}}, PlotArea: plotArea, ShowBlanksAs: "zero"}},
 		{sheetName: "Sheet1", cell: "P30", opts: &Chart{Type: Col3DStacked, Series: series, Format: format, Legend: legend, Title: []RichTextRun{{Text: "3D Stacked Column Chart"}}, PlotArea: plotArea, ShowBlanksAs: "zero", XAxis: ChartAxis{Alignment: Alignment{Vertical: "vert", TextRotation: 0}}}},
 		{sheetName: "Sheet1", cell: "X30", opts: &Chart{Type: Col3DPercentStacked, Series: series, Format: format, Legend: legend, Title: []RichTextRun{{Text: "3D 100% Stacked Column Chart"}}, PlotArea: plotArea, ShowBlanksAs: "zero"}},
 		{sheetName: "Sheet1", cell: "X45", opts: &Chart{Type: Radar, Series: series, Format: format, Legend: ChartLegend{Position: "top_right", ShowLegendKey: false}, Title: []RichTextRun{{Text: "Radar Chart"}}, PlotArea: plotArea, ShowBlanksAs: "span"}},

drawing.go

@@ -80,12 +80,7 @@ func (f *File) addChart(opts *Chart, comboCharts []*Chart) {
 			BackWall: &cThicknessSpPr{
 				Thickness: &attrValInt{Val: intPtr(0)},
 			},
-			PlotArea: &cPlotArea{},
-			Legend: &cLegend{
-				LegendPos: &attrValString{Val: stringPtr(chartLegendPosition[opts.Legend.Position])},
-				Overlay:   &attrValBool{Val: boolPtr(false)},
-			},
-
+			PlotArea:         &cPlotArea{},
 			PlotVisOnly:      &attrValBool{Val: boolPtr(false)},
 			DispBlanksAs:     &attrValString{Val: stringPtr(opts.ShowBlanksAs)},
 			ShowDLblsOverMax: &attrValBool{Val: boolPtr(false)},
@@ -165,9 +160,7 @@ func (f *File) addChart(opts *Chart, comboCharts []*Chart) {
 		Bubble:                      f.drawBubbleChart,
 		Bubble3D:                    f.drawBubbleChart,
 	}
-	if opts.Legend.Position == "none" {
-		xlsxChartSpace.Chart.Legend = nil
-	}
+	xlsxChartSpace.Chart.drawChartLegend(opts)
 	xlsxChartSpace.Chart.PlotArea.SpPr = f.drawShapeFill(opts.PlotArea.Fill, xlsxChartSpace.Chart.PlotArea.SpPr)
 	xlsxChartSpace.Chart.PlotArea.DTable = f.drawPlotAreaDTable(opts)
 	addChart := func(c, p *cPlotArea) {
@@ -881,7 +874,8 @@ func (f *File) drawChartSeriesCat(v ChartSeries, opts *Chart) *cCat {
 func (f *File) drawChartSeriesVal(v ChartSeries, opts *Chart) *cVal {
 	val := &cVal{
 		NumRef: &cNumRef{
-			F: v.Values,
+			F:        v.Values,
+			NumCache: &cNumCache{},
 		},
 	}
 	chartSeriesVal := map[ChartType]*cVal{Scatter: nil, Bubble: nil, Bubble3D: nil}
@@ -935,7 +929,8 @@ func (f *File) drawChartSeriesXVal(v ChartSeries, opts *Chart) *cCat {
 func (f *File) drawChartSeriesYVal(v ChartSeries, opts *Chart) *cVal {
 	val := &cVal{
 		NumRef: &cNumRef{
-			F: v.Values,
+			F:        v.Values,
+			NumCache: &cNumCache{},
 		},
 	}
 	chartSeriesYVal := map[ChartType]*cVal{Scatter: val, Bubble: val, Bubble3D: val}
@@ -954,7 +949,8 @@ func (f *File) drawCharSeriesBubbleSize(v ChartSeries, opts *Chart) *cVal {
 	}
 	return &cVal{
 		NumRef: &cNumRef{
-			F: fVal,
+			F:        fVal,
+			NumCache: &cNumCache{},
 		},
 	}
 }
@@ -1343,6 +1339,36 @@ func (f *File) drawChartLn(opts *ChartLine) *aLn {
 	}
 }
 
+// drawChartLegend provides a function to draw the c:legend element.
+func (c *cChart) drawChartLegend(opts *Chart) {
+	if opts.Legend.Position == "none" {
+		c.Legend = nil
+		return
+	}
+	if c.Legend == nil {
+		c.Legend = &cLegend{
+			LegendPos: &attrValString{Val: stringPtr(chartLegendPosition[opts.Legend.Position])},
+			Overlay:   &attrValBool{Val: boolPtr(false)},
+		}
+	}
+	if opts.Legend.Font != nil {
+		c.Legend.TxPr = &cTxPr{P: aP{PPr: &aPPr{}}}
+		drawChartFont(opts.Legend.Font, &c.Legend.TxPr.P.PPr.DefRPr)
+	}
+	for k := range opts.Series {
+		font := opts.Series[k].Legend.Font
+		if font == nil {
+			continue
+		}
+		legendEntry := cLegendEntry{
+			IDx:  &attrValInt{Val: intPtr(k + opts.order)},
+			TxPr: &cTxPr{P: aP{PPr: &aPPr{}}},
+		}
+		drawChartFont(font, &legendEntry.TxPr.P.PPr.DefRPr)
+		c.Legend.LegendEntry = append(c.Legend.LegendEntry, legendEntry)
+	}
+}
+
 // drawingParser provides a function to parse drawingXML. In order to solve
 // the problem that the label structure is changed after serialization and
 // deserialization, two different structures: decodeWsDr and encodeWsDr are

xmlChart.go

@@ -509,14 +509,22 @@ type cDLbls struct {
 	ShowLeaderLines *attrValBool   `xml:"showLeaderLines"`
 }
 
+// cLegendEntry (Legend Entry) directly maps the legendEntry element. This
+// element specifies the legend entry.
+type cLegendEntry struct {
+	IDx  *attrValInt `xml:"idx"`
+	TxPr *cTxPr      `xml:"txPr"`
+}
+
 // cLegend (Legend) directly maps the legend element. This element specifies
 // the legend.
 type cLegend struct {
-	Layout    *string        `xml:"layout"`
-	LegendPos *attrValString `xml:"legendPos"`
-	Overlay   *attrValBool   `xml:"overlay"`
-	SpPr      *cSpPr         `xml:"spPr"`
-	TxPr      *cTxPr         `xml:"txPr"`
+	Layout      *string        `xml:"layout"`
+	LegendPos   *attrValString `xml:"legendPos"`
+	LegendEntry []cLegendEntry `xml:"legendEntry"`
+	Overlay     *attrValBool   `xml:"overlay"`
+	SpPr        *cSpPr         `xml:"spPr"`
+	TxPr        *cTxPr         `xml:"txPr"`
 }
 
 // cPrintSettings directly maps the printSettings element. This element
@@ -611,6 +619,7 @@ type Chart struct {
 type ChartLegend struct {
 	Position      string
 	ShowLegendKey bool
+	Font          *Font
 }
 
 // ChartMarker directly maps the format settings of the chart marker.
@@ -644,6 +653,7 @@ type ChartSeries struct {
 	Values            string
 	Sizes             string
 	Fill              Fill
+	Legend            ChartLegend
 	Line              ChartLine
 	Marker            ChartMarker
 	DataLabel         ChartDataLabel