Implement Legend with fixed length line on the left side

examples/legend_line_left/main.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"github.com/wcharczuk/go-chart/v2"
+	"os"
+	"time"
+)
+
+func main() {
+	xv, yv := xvalues(), yvalues()
+
+	priceSeries := chart.TimeSeries{
+		Name: "Very long name for a time series to test legend",
+		Style: chart.Style{
+			StrokeColor: chart.GetDefaultColor(0),
+		},
+		XValues: xv,
+		YValues: yv,
+	}
+
+	linRegSeries := &chart.LinearRegressionSeries{
+		Name:        "Regression",
+		InnerSeries: priceSeries,
+	}
+
+	graph := chart.Chart{
+		XAxis: chart.XAxis{
+			TickPosition: chart.TickPositionBetweenTicks,
+		},
+		YAxis: chart.YAxis{
+			Range: &chart.ContinuousRange{
+				Max: 220.0,
+				Min: 180.0,
+			},
+		},
+		Series: []chart.Series{
+			priceSeries,
+			linRegSeries,
+		},
+	}
+
+	graph.Elements = []chart.Renderable{chart.LegendLineLeft(&graph, chart.Style{})}
+
+	f, _ := os.Create("output.png")
+	defer f.Close()
+	graph.Render(chart.PNG, f)
+}
+
+func xvalues() []time.Time {
+	rawx := []string{"2015-07-17", "2015-07-20", "2015-07-21", "2015-07-22", "2015-07-23", "2015-07-24", "2015-07-27", "2015-07-28", "2015-07-29", "2015-07-30", "2015-07-31", "2015-08-03", "2015-08-04", "2015-08-05", "2015-08-06", "2015-08-07", "2015-08-10", "2015-08-11", "2015-08-12", "2015-08-13", "2015-08-14", "2015-08-17", "2015-08-18", "2015-08-19", "2015-08-20", "2015-08-21", "2015-08-24", "2015-08-25", "2015-08-26", "2015-08-27", "2015-08-28", "2015-08-31", "2015-09-01", "2015-09-02", "2015-09-03", "2015-09-04", "2015-09-08", "2015-09-09", "2015-09-10", "2015-09-11", "2015-09-14", "2015-09-15", "2015-09-16", "2015-09-17", "2015-09-18", "2015-09-21", "2015-09-22", "2015-09-23", "2015-09-24", "2015-09-25", "2015-09-28", "2015-09-29", "2015-09-30", "2015-10-01", "2015-10-02", "2015-10-05", "2015-10-06", "2015-10-07", "2015-10-08", "2015-10-09", "2015-10-12", "2015-10-13", "2015-10-14", "2015-10-15", "2015-10-16", "2015-10-19", "2015-10-20", "2015-10-21", "2015-10-22", "2015-10-23", "2015-10-26", "2015-10-27", "2015-10-28", "2015-10-29", "2015-10-30", "2015-11-02", "2015-11-03", "2015-11-04", "2015-11-05", "2015-11-06", "2015-11-09", "2015-11-10", "2015-11-11", "2015-11-12", "2015-11-13", "2015-11-16", "2015-11-17", "2015-11-18", "2015-11-19", "2015-11-20", "2015-11-23", "2015-11-24", "2015-11-25", "2015-11-27", "2015-11-30", "2015-12-01", "2015-12-02", "2015-12-03", "2015-12-04", "2015-12-07", "2015-12-08", "2015-12-09", "2015-12-10", "2015-12-11", "2015-12-14", "2015-12-15", "2015-12-16", "2015-12-17", "2015-12-18", "2015-12-21", "2015-12-22", "2015-12-23", "2015-12-24", "2015-12-28", "2015-12-29", "2015-12-30", "2015-12-31", "2016-01-04", "2016-01-05", "2016-01-06", "2016-01-07", "2016-01-08", "2016-01-11", "2016-01-12", "2016-01-13", "2016-01-14", "2016-01-15", "2016-01-19", "2016-01-20", "2016-01-21", "2016-01-22", "2016-01-25", "2016-01-26", "2016-01-27", "2016-01-28", "2016-01-29", "2016-02-01", "2016-02-02", "2016-02-03", "2016-02-04", "2016-02-05", "2016-02-08", "2016-02-09", "2016-02-10", "2016-02-11", "2016-02-12", "2016-02-16", "2016-02-17", "2016-02-18", "2016-02-19", "2016-02-22", "2016-02-23", "2016-02-24", "2016-02-25", "2016-02-26", "2016-02-29", "2016-03-01", "2016-03-02", "2016-03-03", "2016-03-04", "2016-03-07", "2016-03-08", "2016-03-09", "2016-03-10", "2016-03-11", "2016-03-14", "2016-03-15", "2016-03-16", "2016-03-17", "2016-03-18", "2016-03-21", "2016-03-22", "2016-03-23", "2016-03-24", "2016-03-28", "2016-03-29", "2016-03-30", "2016-03-31", "2016-04-01", "2016-04-04", "2016-04-05", "2016-04-06", "2016-04-07", "2016-04-08", "2016-04-11", "2016-04-12", "2016-04-13", "2016-04-14", "2016-04-15", "2016-04-18", "2016-04-19", "2016-04-20", "2016-04-21", "2016-04-22", "2016-04-25", "2016-04-26", "2016-04-27", "2016-04-28", "2016-04-29", "2016-05-02", "2016-05-03", "2016-05-04", "2016-05-05", "2016-05-06", "2016-05-09", "2016-05-10", "2016-05-11", "2016-05-12", "2016-05-13", "2016-05-16", "2016-05-17", "2016-05-18", "2016-05-19", "2016-05-20", "2016-05-23", "2016-05-24", "2016-05-25", "2016-05-26", "2016-05-27", "2016-05-31", "2016-06-01", "2016-06-02", "2016-06-03", "2016-06-06", "2016-06-07", "2016-06-08", "2016-06-09", "2016-06-10", "2016-06-13", "2016-06-14", "2016-06-15", "2016-06-16", "2016-06-17", "2016-06-20", "2016-06-21", "2016-06-22", "2016-06-23", "2016-06-24", "2016-06-27", "2016-06-28", "2016-06-29", "2016-06-30", "2016-07-01", "2016-07-05", "2016-07-06", "2016-07-07", "2016-07-08", "2016-07-11", "2016-07-12", "2016-07-13", "2016-07-14", "2016-07-15"}
+
+	var dates []time.Time
+	for _, ts := range rawx {
+		parsed, _ := time.Parse(chart.DefaultDateFormat, ts)
+		dates = append(dates, parsed)
+	}
+	return dates
+}
+
+func yvalues() []float64 {
+	return []float64{212.47, 212.59, 211.76, 211.37, 210.18, 208.00, 206.79, 209.33, 210.77, 210.82, 210.50, 209.79, 209.38, 210.07, 208.35, 207.95, 210.57, 208.66, 208.92, 208.66, 209.42, 210.59, 209.98, 208.32, 203.97, 197.83, 189.50, 187.27, 194.46, 199.27, 199.28, 197.67, 191.77, 195.41, 195.55, 192.59, 197.43, 194.79, 195.85, 196.74, 196.01, 198.45, 200.18, 199.73, 195.45, 196.46, 193.90, 193.60, 192.90, 192.87, 188.01, 188.12, 191.63, 192.13, 195.00, 198.47, 197.79, 199.41, 201.21, 201.33, 201.52, 200.25, 199.29, 202.35, 203.27, 203.37, 203.11, 201.85, 205.26, 207.51, 207.00, 206.60, 208.95, 208.83, 207.93, 210.39, 211.00, 210.36, 210.15, 210.04, 208.08, 208.56, 207.74, 204.84, 202.54, 205.62, 205.47, 208.73, 208.55, 209.31, 209.07, 209.35, 209.32, 209.56, 208.69, 210.68, 208.53, 205.61, 209.62, 208.35, 206.95, 205.34, 205.87, 201.88, 202.90, 205.03, 208.03, 204.86, 200.02, 201.67, 203.50, 206.02, 205.68, 205.21, 207.40, 205.93, 203.87, 201.02, 201.36, 198.82, 194.05, 191.92, 192.11, 193.66, 188.83, 191.93, 187.81, 188.06, 185.65, 186.69, 190.52, 187.64, 190.20, 188.13, 189.11, 193.72, 193.65, 190.16, 191.30, 191.60, 187.95, 185.42, 185.43, 185.27, 182.86, 186.63, 189.78, 192.88, 192.09, 192.00, 194.78, 192.32, 193.20, 195.54, 195.09, 193.56, 198.11, 199.00, 199.78, 200.43, 200.59, 198.40, 199.38, 199.54, 202.76, 202.50, 202.17, 203.34, 204.63, 204.38, 204.67, 204.56, 203.21, 203.12, 203.24, 205.12, 206.02, 205.52, 206.92, 206.25, 204.19, 206.42, 203.95, 204.50, 204.02, 205.92, 208.00, 208.01, 207.78, 209.24, 209.90, 210.10, 208.97, 208.97, 208.61, 208.92, 209.35, 207.45, 206.33, 207.97, 206.16, 205.01, 204.97, 205.72, 205.89, 208.45, 206.50, 206.56, 204.76, 206.78, 204.85, 204.91, 204.20, 205.49, 205.21, 207.87, 209.28, 209.34, 210.24, 209.84, 210.27, 210.91, 210.28, 211.35, 211.68, 212.37, 212.08, 210.07, 208.45, 208.04, 207.75, 208.37, 206.52, 207.85, 208.44, 208.10, 210.81, 203.24, 199.60, 203.20, 206.66, 209.48, 209.92, 208.41, 209.66, 209.53, 212.65, 213.40, 214.95, 214.92, 216.12, 215.83}
+}

legend.go

@@ -118,6 +118,125 @@ func Legend(c *Chart, userDefaults ...Style) Renderable {
 	}
 }
 
+// LegendLineLeft is a legend with the line drawn left to the legend text.
+func LegendLineLeft(c *Chart, userDefaults ...Style) Renderable {
+	return func(r Renderer, cb Box, chartDefaults Style) {
+		legendDefaults := Style{
+			FillColor:   drawing.ColorWhite,
+			FontColor:   DefaultTextColor,
+			FontSize:    8.0,
+			StrokeColor: DefaultAxisColor,
+			StrokeWidth: DefaultAxisLineWidth,
+			Padding: Box{
+				Top:    5,
+				Left:   5,
+				Right:  5,
+				Bottom: 5,
+			},
+		}
+
+		var legendStyle Style
+		if len(userDefaults) > 0 {
+			legendStyle = userDefaults[0].InheritFrom(chartDefaults.InheritFrom(legendDefaults))
+		} else {
+			legendStyle = chartDefaults.InheritFrom(legendDefaults)
+		}
+
+		// DEFAULTS
+		lineTextGap := 5
+		lineLengthMinimum := 25
+		strokeLength := 17
+
+		var labels []string
+		var lines []Style
+		for index, s := range c.Series {
+			if !s.GetStyle().Hidden {
+				if _, isAnnotationSeries := s.(AnnotationSeries); !isAnnotationSeries {
+					labels = append(labels, s.GetName())
+					lines = append(lines, s.GetStyle().InheritFrom(c.styleDefaultsSeries(index)))
+				}
+			}
+		}
+
+		legend := Box{
+			Top:  cb.Top,
+			Left: cb.Left,
+			// bottom and right will be sized by the legend content + relevant padding.
+		}
+
+		legendContent := Box{
+			Top:    legend.Top + legendStyle.Padding.Top,
+			Left:   legend.Left + legendStyle.Padding.Left,
+			Right:  legend.Left + legendStyle.Padding.Left,
+			Bottom: legend.Top + legendStyle.Padding.Top,
+		}
+
+		legendStyle.GetTextOptions().WriteToRenderer(r)
+
+		// measure
+		labelCount := 0
+		for x := 0; x < len(labels); x++ {
+			if len(labels[x]) > 0 {
+				tb := r.MeasureText(labels[x])
+				if labelCount > 0 {
+					legendContent.Bottom += DefaultMinimumTickVerticalSpacing
+				}
+				legendContent.Bottom += tb.Height()
+				right := legendContent.Left + tb.Width() + lineTextGap + lineLengthMinimum
+				legendContent.Right = MaxInt(legendContent.Right, right)
+				labelCount++
+			}
+		}
+
+		legend = legend.Grow(legendContent)
+		legend.Right = legendContent.Right + legendStyle.Padding.Right
+		legend.Bottom = legendContent.Bottom + legendStyle.Padding.Bottom
+
+		Draw.Box(r, legend, legendStyle)
+
+		legendStyle.GetTextOptions().WriteToRenderer(r)
+
+		ycursor := legendContent.Top
+		lx := legendContent.Left
+		legendCount := 0
+		var label string
+		for x := 0; x < len(labels); x++ {
+			label = labels[x]
+			if len(label) > 0 {
+				if legendCount > 0 {
+					ycursor += DefaultMinimumTickVerticalSpacing
+				}
+
+				// Calculate text dimensions
+				tb := r.MeasureText(label)
+				ty := ycursor + tb.Height()
+				th2 := tb.Height() >> 1
+
+				// Calculate line x and y coordinates
+				ly := ty - th2
+
+				// Calculate line ending x coordinate
+				lx2 := lx + strokeLength
+
+				r.SetStrokeColor(lines[x].GetStrokeColor())
+				r.SetStrokeWidth(lines[x].GetStrokeWidth())
+				r.SetStrokeDashArray(lines[x].GetStrokeDashArray())
+
+				r.MoveTo(lx, ly)
+				r.LineTo(lx2, ly)
+				r.Stroke()
+
+				// Calculate Text starting coordinates
+				textX := lx2 + lineTextGap
+				r.Text(label, textX, ty)
+
+				ycursor += tb.Height()
+				legendCount++
+			}
+		}
+	}
+}
+
 // LegendThin is a legend that doesn't obscure the chart area.
 func LegendThin(c *Chart, userDefaults ...Style) Renderable {
 	return func(r Renderer, cb Box, chartDefaults Style) {