feat: support rotate series label

bar_chart.go

@@ -23,6 +23,8 @@
 package charts
 
 import (
+	"math"
+
 	"github.com/golang/freetype/truetype"
 	"github.com/wcharczuk/go-chart/v2"
 )
@@ -164,11 +166,26 @@ func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (B
 			if labelPainter == nil {
 				continue
 			}
+			y := barMaxHeight - h
+			radians := float64(0)
+			var fontColor Color
+			if series.Label.Position == PositionBottom {
+				y = barMaxHeight
+				radians = -math.Pi / 2
+				if isLightColor(fillColor) {
+					fontColor = defaultLightFontColor
+				} else {
+					fontColor = defaultDarkFontColor
+				}
+			}
 			labelPainter.Add(LabelValue{
 				Index: index,
 				Value: item.Value,
 				X:     x + barWidth>>1,
-				Y:     barMaxHeight - h,
+				Y:     y,
+				// 旋转
+				Radians:   radians,
+				FontColor: fontColor,
 			})
 		}
 

examples/charts/main.go

@@ -355,6 +355,10 @@ func indexHandler(w http.ResponseWriter, req *http.Request) {
 							Value: 180,
 						},
 					},
+					Label: charts.SeriesLabel{
+						Show:     true,
+						Position: charts.PositionBottom,
+					},
 				},
 			},
 		},

painter.go

@@ -560,7 +560,14 @@ func (p *Painter) Text(body string, x, y int) *Painter {
 
 func (p *Painter) TextRotation(body string, x, y int, radians float64) {
 	p.render.SetTextRotation(radians)
-	p.render.Text(body, x, y)
+	p.render.Text(body, x+p.box.Left, y+p.box.Top)
+	p.render.ClearTextRotation()
+}
+
+func (p *Painter) SetTextRotation(radians float64) {
+	p.render.SetTextRotation(radians)
+}
+func (p *Painter) ClearTextRotation() {
 	p.render.ClearTextRotation()
 }
 

series.go

@@ -79,6 +79,8 @@ type SeriesLabel struct {
 	Show bool
 	// Distance to the host graphic element.
 	Distance int
+	// The position of label
+	Position string
 }
 
 const (

series_label.go

@@ -32,6 +32,8 @@ type labelRenderValue struct {
 	Style Style
 	X     int
 	Y     int
+	// 旋转
+	Radians float64
 }
 
 type LabelValue struct {
@@ -39,6 +41,10 @@ type LabelValue struct {
 	Value float64
 	X     int
 	Y     int
+	// 旋转
+	Radians float64
+	// 字体颜色
+	FontColor Color
 }
 
 type SeriesLabelPainter struct {
@@ -81,27 +87,45 @@ func (o *SeriesLabelPainter) Add(value LabelValue) {
 		FontSize:  labelFontSize,
 		Font:      o.font,
 	}
+	if !value.FontColor.IsZero() {
+		label.Color = value.FontColor
+	}
 	if !label.Color.IsZero() {
 		labelStyle.FontColor = label.Color
 	}
-	o.p.OverrideDrawingStyle(labelStyle)
+	p := o.p
-	textBox := o.p.MeasureText(text)
+	p.OverrideDrawingStyle(labelStyle)
+	rotated := value.Radians != 0
+	if rotated {
+		p.SetTextRotation(value.Radians)
+	}
+	textBox := p.MeasureText(text)
 	renderValue := labelRenderValue{
 		Text:    text,
 		Style:   labelStyle,
 		X:       value.X - textBox.Width()>>1,
 		Y:       value.Y - distance,
+		Radians: value.Radians,
 	}
+	if rotated {
+		renderValue.X = value.X + textBox.Width()>>1 - 1
+		p.ClearTextRotation()
+	} else {
 		if textBox.Width()%2 != 0 {
 			renderValue.X++
 		}
+	}
 	o.values = append(o.values, renderValue)
 }
 
 func (o *SeriesLabelPainter) Render() (Box, error) {
 	for _, item := range o.values {
 		o.p.OverrideTextStyle(item.Style)
+		if item.Radians != 0 {
+			o.p.TextRotation(item.Text, item.X, item.Y, item.Radians)
+		} else {
 			o.p.Text(item.Text, item.X, item.Y)
 		}
+	}
 	return chart.BoxZero, nil
 }