feat: implement legend type with fixed length line on the left side

fixes wcharczuk#185

legend.go

@@ -118,6 +118,124 @@ 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,
+ }
+
+ 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().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 + 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 = 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
+ 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 + lineLengthMinimum
+
+ 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) {