slight tweak to legend (adds a new style) and example

_examples/legend_left/main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+
+	/*
+	   In this example we add a `Renderable` or a custom component to the `Elements` array.
+	   In this specific case it is a pre-built renderable (`CreateLegend`) that draws a legend for the chart's series.
+	   If you like, you can use `CreateLegend` as a template for writing your own renderable, or even your own legend.
+	*/
+
+	graph := chart.Chart{
+		XAxis: chart.XAxis{
+			Style: chart.Style{Show: true},
+		},
+		YAxis: chart.YAxis{
+			Style: chart.Style{Show: true},
+		},
+		Background: chart.Style{
+			Padding: chart.Box{
+				Top:  20,
+				Left: 260,
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				Name:    "A test series",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Another test series",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Yet Another test series",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Even More series",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Foo Bar",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Bar Baz",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Free Yourself",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Wheres Ja?",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "Fast and the Furious",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{5.0, 4.0, 3.0, 2.0, 1.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "2 Fast 2 Furious",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{5.0, 4.0, 3.0, 2.0, 1.0},
+			},
+
+			chart.ContinuousSeries{
+				Name:    "They only get more fast and more furious",
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{5.0, 4.0, 3.0, 2.0, 1.0},
+			},
+		},
+	}
+
+	//note we have to do this as a separate step because we need a reference to graph
+	graph.Elements = []chart.Renderable{
+		chart.LegendLeft(&graph),
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	graph.Render(chart.PNG, res)
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	http.ListenAndServe(":8080", nil)
+}

legend.go

@@ -213,3 +213,117 @@ func LegendThin(c *Chart, userDefaults ...Style) Renderable {
 		}
 	}
 }
+
+// LegendLeft is a legend that is designed for longer series lists.
+func LegendLeft(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,
+		}
+
+		var legendStyle Style
+		if len(userDefaults) > 0 {
+			legendStyle = userDefaults[0].InheritFrom(chartDefaults.InheritFrom(legendDefaults))
+		} else {
+			legendStyle = chartDefaults.InheritFrom(legendDefaults)
+		}
+
+		// DEFAULTS
+		legendPadding := Box{
+			Top:    5,
+			Left:   5,
+			Right:  5,
+			Bottom: 5,
+		}
+		lineTextGap := 5
+		lineLengthMinimum := 25
+
+		var labels []string
+		var lines []Style
+		for index, s := range c.Series {
+			if s.GetStyle().IsZero() || s.GetStyle().Show {
+				if _, isAnnotationSeries := s.(AnnotationSeries); !isAnnotationSeries {
+					labels = append(labels, s.GetName())
+					lines = append(lines, s.GetStyle().InheritFrom(c.styleDefaultsSeries(index)))
+				}
+			}
+		}
+
+		legend := Box{
+			Top:  5,
+			Left: 5,
+			// bottom and right will be sized by the legend content + relevant padding.
+		}
+
+		legendContent := Box{
+			Top:    legend.Top + legendPadding.Top,
+			Left:   legend.Left + legendPadding.Left,
+			Right:  legend.Left + legendPadding.Left,
+			Bottom: legend.Top + legendPadding.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 = Math.MaxInt(legendContent.Right, right)
+				labelCount++
+			}
+		}
+
+		legend = legend.Grow(legendContent)
+		legend.Right = legendContent.Right + legendPadding.Right
+		legend.Bottom = legendContent.Bottom + legendPadding.Bottom
+
+		Draw.Box(r, legend, legendStyle)
+
+		legendStyle.GetTextOptions().WriteToRenderer(r)
+
+		ycursor := legendContent.Top
+		tx := 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
+				}
+
+				tb := r.MeasureText(label)
+
+				ty := ycursor + tb.Height()
+				r.Text(label, tx, ty)
+
+				th2 := tb.Height() >> 1
+
+				lx := tx + tb.Width() + lineTextGap
+				ly := ty - th2
+				lx2 := legendContent.Right - legendPadding.Right
+
+				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()
+
+				ycursor += tb.Height()
+				legendCount++
+			}
+		}
+	}
+}