feat: support legend render

examples/painter/main.go

@@ -26,7 +26,7 @@ func writeFile(buf []byte) error {
 
 func main() {
 	p, err := charts.NewPainter(charts.PainterOptions{
-		Width:  400,
+		Width:  600,
 		Height: 1200,
 		Type:   charts.ChartOutputPNG,
 	})
@@ -422,6 +422,60 @@ func main() {
 		StrokeColor:    drawing.ColorBlue,
 	}).Render()
 
+	top += 100
+	charts.NewLegendPainter(p.Child(charts.PainterBoxOption(charts.Box{
+		Top:    top,
+		Left:   1,
+		Right:  p.Width() - 1,
+		Bottom: top + 30,
+	})), charts.LegendPainterOption{
+		Data: []string{
+			"Email",
+			"Union Ads",
+			"Video Ads",
+			"Direct",
+		},
+		FontSize:  12,
+		FontColor: drawing.ColorBlack,
+	}).Render()
+
+	top += 30
+	charts.NewLegendPainter(p.Child(charts.PainterBoxOption(charts.Box{
+		Top:    top,
+		Left:   1,
+		Right:  p.Width() - 1,
+		Bottom: top + 30,
+	})), charts.LegendPainterOption{
+		Data: []string{
+			"Email",
+			"Union Ads",
+			"Video Ads",
+			"Direct",
+		},
+		Align:     charts.AlignRight,
+		FontSize:  16,
+		Icon:      charts.IconRect,
+		FontColor: drawing.ColorBlack,
+	}).Render()
+
+	top += 30
+	charts.NewLegendPainter(p.Child(charts.PainterBoxOption(charts.Box{
+		Top:    top,
+		Left:   1,
+		Right:  p.Width() - 1,
+		Bottom: top + 100,
+	})), charts.LegendPainterOption{
+		Data: []string{
+			"Email",
+			"Union Ads",
+			"Video Ads",
+			"Direct",
+		},
+		Orient:    charts.OrientVertical,
+		FontSize:  12,
+		FontColor: drawing.ColorBlack,
+	}).Render()
+
 	buf, err := p.Bytes()
 	if err != nil {
 		panic(err)

legend.go

@@ -0,0 +1,154 @@
+// MIT License
+
+// Copyright (c) 2022 Tree Xie
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package charts
+
+type LegendPainter struct {
+	p   *Painter
+	opt *LegendPainterOption
+}
+
+const IconRect = "rect"
+const IconLineDot = "lineDot"
+
+type LegendPainterOption struct {
+	Theme ColorPalette
+	// Text array of legend
+	Data []string
+	// Distance between legend component and the left side of the container.
+	// It can be pixel value: 20, percentage value: 20%,
+	// or position value: right, center.
+	Left string
+	// Distance between legend component and the top side of the container.
+	// It can be pixel value: 20.
+	Top string
+	// Legend marker and text aligning, it can be left or right, default is left.
+	Align string
+	// The layout orientation of legend, it can be horizontal or vertical, default is horizontal.
+	Orient string
+	// Icon of the legend.
+	Icon string
+	// Font size of legend text
+	FontSize float64
+	// FontColor color of legend text
+	FontColor Color
+}
+
+func NewLegendPainter(p *Painter, opt LegendPainterOption) *LegendPainter {
+	return &LegendPainter{
+		p:   p,
+		opt: &opt,
+	}
+}
+
+func (l *LegendPainter) Render() (Box, error) {
+	opt := l.opt
+	theme := opt.Theme
+	if theme == nil {
+		theme = l.p.theme
+	}
+	p := l.p
+	p.SetTextStyle(Style{
+		FontSize:  opt.FontSize,
+		FontColor: opt.FontColor,
+	})
+	measureList := make([]Box, len(opt.Data))
+	maxTextWidth := 0
+	for index, text := range opt.Data {
+		b := p.MeasureText(text)
+		if b.Width() > maxTextWidth {
+			maxTextWidth = b.Width()
+		}
+		measureList[index] = b
+	}
+	x := 0
+	y := 0
+	offset := 20
+	textOffset := 2
+	legendWidth := 30
+	legendHeight := 20
+	drawIcon := func(top, left int) int {
+		if opt.Icon == IconRect {
+			p.Rect(Box{
+				Top:    top - legendHeight + 4,
+				Left:   left,
+				Right:  left + legendWidth,
+				Bottom: top - 2,
+			})
+		} else {
+			p.LegendLineDot(Box{
+				Top:    top,
+				Left:   left,
+				Right:  left + legendWidth,
+				Bottom: top + legendHeight,
+			})
+		}
+		return left + legendWidth
+	}
+	for index, text := range opt.Data {
+		color := theme.GetSeriesColor(index)
+		p.SetDrawingStyle(Style{
+			FillColor:   color,
+			StrokeColor: color,
+		})
+		if opt.Align != AlignRight {
+			x = drawIcon(y, x)
+			x += textOffset
+		}
+		p.Text(text, x, y)
+		x += measureList[index].Width()
+		if opt.Align == AlignRight {
+			x += textOffset
+			x = drawIcon(0, x)
+		}
+		if opt.Orient == OrientVertical {
+			y += offset
+			x = 0
+		} else {
+			x += offset
+			y = 0
+		}
+	}
+	width := 0
+	height := 0
+	for _, item := range measureList {
+		if opt.Orient == OrientVertical {
+			height += item.Height()
+		} else {
+			width += item.Width()
+		}
+	}
+	if opt.Orient == OrientVertical {
+		width = maxTextWidth + textOffset + legendWidth
+		height = offset * len(opt.Data)
+	} else {
+		height = legendHeight
+		offsetValue := (len(opt.Data) - 1) * (offset + textOffset)
+		allLegendWidth := len(opt.Data) * legendWidth
+		width += (offsetValue + allLegendWidth)
+	}
+
+	return Box{
+		Right:  width,
+		Bottom: height,
+	}, nil
+}

painter.go

@@ -170,6 +170,9 @@ func NewPainter(opts PainterOptions, opt ...PainterOption) (*Painter, error) {
 		font: font,
 	}
 	p.setOptions(opt...)
+	if p.theme == nil {
+		p.theme = NewTheme(ThemeLight)
+	}
 	return p, nil
 }
 func (p *Painter) setOptions(opts ...PainterOption) {
@@ -705,11 +708,11 @@ func (p *Painter) LegendLineDot(box Box) *Painter {
 	dotHeight := 5
 
 	p.render.SetStrokeWidth(float64(strokeWidth))
-	center := (height - strokeWidth) >> 1
+	center := (height-strokeWidth)>>1 - 1
-	p.MoveTo(box.Left, box.Top+center)
+	p.MoveTo(box.Left, box.Top-center)
-	p.LineTo(box.Right, box.Top+center)
+	p.LineTo(box.Right, box.Top-center)
 	p.Stroke()
-	p.Circle(float64(dotHeight), box.Left+width>>1, center)
+	p.Circle(float64(dotHeight), box.Left+width>>1, box.Top-center)
 	p.FillStroke()
 	return p
 }