refactor: adjust series label render

series_label.go

@@ -22,29 +22,80 @@
 
 package charts
 
-import "github.com/wcharczuk/go-chart/v2"
+import (
+	"github.com/golang/freetype/truetype"
+	"github.com/wcharczuk/go-chart/v2"
+)
 
-type LabelValue struct {
+type labelRenderValue struct {
 	Text  string
 	Style Style
 	X     int
 	Y     int
 }
 
-type SeriesLabelPainter struct {
-	p      *Painter
-	values []LabelValue
+type LabelValue struct {
+	Index int
+	Value float64
+	X     int
+	Y     int
 }
 
-func NewSeriesLabelPainter(p *Painter) *SeriesLabelPainter {
+type SeriesLabelPainter struct {
+	p           *Painter
+	seriesNames []string
+	label       *SeriesLabel
+	theme       ColorPalette
+	font        *truetype.Font
+	values      []labelRenderValue
+}
+
+type SeriesLabelPainterParams struct {
+	P           *Painter
+	SeriesNames []string
+	Label       SeriesLabel
+	Theme       ColorPalette
+	Font        *truetype.Font
+}
+
+func NewSeriesLabelPainter(params SeriesLabelPainterParams) *SeriesLabelPainter {
 	return &SeriesLabelPainter{
-		p:      p,
-		values: make([]LabelValue, 0),
+		p:           params.P,
+		seriesNames: params.SeriesNames,
+		label:       &params.Label,
+		theme:       params.Theme,
+		font:        params.Font,
+		values:      make([]labelRenderValue, 0),
 	}
 }
 
 func (o *SeriesLabelPainter) Add(value LabelValue) {
-	o.values = append(o.values, value)
+	label := o.label
+	distance := label.Distance
+	if distance == 0 {
+		distance = 5
+	}
+	text := NewValueLabelFormatter(o.seriesNames, label.Formatter)(value.Index, value.Value, -1)
+	labelStyle := Style{
+		FontColor: o.theme.GetTextColor(),
+		FontSize:  labelFontSize,
+		Font:      o.font,
+	}
+	if !label.Color.IsZero() {
+		labelStyle.FontColor = label.Color
+	}
+	o.p.OverrideDrawingStyle(labelStyle)
+	textBox := o.p.MeasureText(text)
+	renderValue := labelRenderValue{
+		Text:  text,
+		Style: labelStyle,
+		X:     value.X - textBox.Width()>>1,
+		Y:     value.Y - distance,
+	}
+	if textBox.Width()%2 != 0 {
+		renderValue.X++
+	}
+	o.values = append(o.values, renderValue)
 }
 
 func (o *SeriesLabelPainter) Render() (Box, error) {