updates

chart.go

@@ -17,10 +17,9 @@ type Chart struct {
 	Height int
 	DPI    float64
 
-	Background      Style
+	Background Style
-	Canvas          Style
+	Canvas     Style
-	Axes            Style
+	Axes       Style
-	FinalValueLabel Style
 
 	XRange Range
 	YRange Range
@@ -53,21 +52,20 @@ func (c Chart) GetFont() (*truetype.Font, error) {
 }
 
 // Render renders the chart with the given renderer to the given io.Writer.
-func (c *Chart) Render(provider RendererProvider, w io.Writer) error {
+func (c *Chart) Render(rp RendererProvider, w io.Writer) error {
 	if len(c.Series) == 0 {
 		return errors.New("Please provide at least one series")
 	}
-	r, err := provider(c.Width, c.Height)
+	r, err := rp(c.Width, c.Height)
 	if err != nil {
 		return err
 	}
-	if c.hasText() {
+
-		font, err := c.GetFont()
+	font, err := c.GetFont()
-		if err != nil {
+	if err != nil {
-			return err
+		return err
-		}
-		r.SetFont(font)
 	}
+	r.SetFont(font)
 	r.SetDPI(c.GetDPI(DefaultDPI))
 
 	canvasBox := c.calculateCanvasBox(r)
@@ -77,16 +75,12 @@ func (c *Chart) Render(provider RendererProvider, w io.Writer) error {
 	c.drawCanvas(r, canvasBox)
 	c.drawAxes(r, canvasBox, xrange, yrange)
 	for index, series := range c.Series {
-		c.drawSeries(r, canvasBox, index, series, xrange, yrange)
+		c.drawSeries(r, canvasBox, series, xrange, yrange)
 	}
 	c.drawTitle(r)
 	return r.Save(w)
 }
 
-func (c Chart) hasText() bool {
-	return c.TitleStyle.Show || c.Axes.Show || c.FinalValueLabel.Show
-}
-
 func (c Chart) getAxisWidth() int {
 	asw := 0
 	if c.Axes.Show {
@@ -119,21 +113,19 @@ func (c Chart) calculateCanvasBox(r Renderer) Box {
 }
 
 func (c Chart) calculateFinalLabelWidth(r Renderer) int {
-	if !c.FinalValueLabel.Show {
-		return 0
-	}
-
 	var finalLabelText string
 	for _, s := range c.Series {
-		_, lv := s.GetValue(s.Len() - 1)
+		if vs, isValueProvider := s.(ValueProvider); isValueProvider {
-		var ll string
+			_, lv := vs.GetValue(vs.Len() - 1)
-		if c.YRange.Formatter != nil {
+			var ll string
-			ll = c.YRange.Formatter(lv)
+			if c.YRange.Formatter != nil {
-		} else {
+				ll = c.YRange.Formatter(lv)
-			ll = s.GetYFormatter()(lv)
+			} else if fp, isFormatterProvider := s.(FormatterProvider); isFormatterProvider {
-		}
+				ll = fp.GetYFormatter()(lv)
-		if len(finalLabelText) < len(ll) {
+			}
-			finalLabelText = ll
+			if len(finalLabelText) < len(ll) {
+				finalLabelText = ll
+			}
 		}
 	}
 
@@ -145,7 +137,7 @@ func (c Chart) calculateFinalLabelWidth(r Renderer) int {
 	pr := c.FinalValueLabel.Padding.GetRight(DefaultFinalLabelPadding.Right)
 	lsw := int(c.FinalValueLabel.GetStrokeWidth(DefaultAxisLineWidth))
 
-	return DefaultFinalLabelDeltaWidth +
+	return DefaultYAxisMargin +
 		pl + pr +
 		textWidth + asw + 2*lsw
 }
@@ -163,33 +155,37 @@ func (c Chart) initRanges(canvasBox Box) (xrange Range, yrange Range) {
 	var globalMinY, globalMinX float64
 	var globalMaxY, globalMaxX float64
 	for _, s := range c.Series {
-		seriesLength := s.Len()
+		if vp, isValueProvider := s.(ValueProvider); isValueProvider {
-		for index := 0; index < seriesLength; index++ {
+			seriesLength := vp.Len()
-			vx, vy := s.GetValue(index)
+			for index := 0; index < seriesLength; index++ {
-			if didSetFirstValues {
+				vx, vy := vp.GetValue(index)
-				if globalMinX > vx {
+				if didSetFirstValues {
-					globalMinX = vx
+					if globalMinX > vx {
+						globalMinX = vx
+					}
+					if globalMinY > vy {
+						globalMinY = vy
+					}
+					if globalMaxX < vx {
+						globalMaxX = vx
+					}
+					if globalMaxY < vy {
+						globalMaxY = vy
+					}
+				} else {
+					globalMinX, globalMaxX = vx, vx
+					globalMinY, globalMaxY = vy, vy
+					didSetFirstValues = true
 				}
-				if globalMinY > vy {
-					globalMinY = vy
-				}
-				if globalMaxX < vx {
-					globalMaxX = vx
-				}
-				if globalMaxY < vy {
-					globalMaxY = vy
-				}
-			} else {
-				globalMinX, globalMaxX = vx, vx
-				globalMinY, globalMaxY = vy, vy
-				didSetFirstValues = true
 			}
 		}
-		if xrange.Formatter == nil {
+		if fp, isFormatterProvider := s.(FormatterProvider); isFormatterProvider {
-			xrange.Formatter = s.GetXFormatter()
+			if xrange.Formatter == nil {
-		}
+				xrange.Formatter = fp.GetXFormatter()
-		if yrange.Formatter == nil {
+			}
-			yrange.Formatter = s.GetYFormatter()
+			if yrange.Formatter == nil {
+				yrange.Formatter = fp.GetYFormatter()
+			}
 		}
 	}
 
@@ -281,7 +277,7 @@ func (c Chart) generateRangeTicks(r Range, tickCount int, offset float64) []Tick
 func (c Chart) drawYAxisLabels(r Renderer, canvasBox Box, yrange Range) {
 	tickFontSize := c.Axes.GetFontSize(DefaultAxisFontSize)
 	asw := c.getAxisWidth()
-	tx := canvasBox.Right + DefaultFinalLabelDeltaWidth + asw
+	tx := canvasBox.Right + DefaultYAxisMargin + asw
 
 	r.SetFontColor(c.Axes.GetFontColor(DefaultAxisColor))
 	r.SetFontSize(tickFontSize)
@@ -332,111 +328,8 @@ func (c Chart) drawXAxisLabels(r Renderer, canvasBox Box, xrange Range) {
 	}
 }
 
-func (c Chart) drawSeries(r Renderer, canvasBox Box, index int, s Series, xrange, yrange Range) {
+func (c Chart) drawSeries(r Renderer, canvasBox Box, s Series, xrange, yrange Range) {
-	if s.Len() == 0 {
+	return s.Render(&c, r, canvasBox, xrange, yrange)
-		return
-	}
-
-	cx := canvasBox.Left
-	cy := canvasBox.Top
-	cb := canvasBox.Bottom
-	cw := canvasBox.Width
-
-	v0x, v0y := s.GetValue(0)
-	x0 := cw - xrange.Translate(v0x)
-	y0 := yrange.Translate(v0y)
-
-	var vx, vy float64
-	var x, y int
-
-	fill := s.GetStyle().GetFillColor()
-	if !fill.IsZero() {
-		r.SetFillColor(fill)
-		r.MoveTo(x0+cx, y0+cy)
-		for i := 1; i < s.Len(); i++ {
-			vx, vy = s.GetValue(i)
-			x = cw - xrange.Translate(vx)
-			y = yrange.Translate(vy)
-			r.LineTo(x+cx, y+cy)
-		}
-		r.LineTo(x+cx, cb)
-		r.LineTo(x0+cx, cb)
-		r.Close()
-		r.Fill()
-	}
-
-	stroke := s.GetStyle().GetStrokeColor(GetDefaultSeriesStrokeColor(index))
-	r.SetStrokeColor(stroke)
-	r.SetStrokeWidth(s.GetStyle().GetStrokeWidth(DefaultStrokeWidth))
-
-	r.MoveTo(x0+cx, y0+cy)
-	for i := 1; i < s.Len(); i++ {
-		vx, vy = s.GetValue(i)
-		x = cw - xrange.Translate(vx)
-		y = yrange.Translate(vy)
-		r.LineTo(x+cx, y+cy)
-	}
-	r.Stroke()
-
-	c.drawFinalValueLabel(r, canvasBox, index, s, yrange)
-}
-
-func (c Chart) drawFinalValueLabel(r Renderer, canvasBox Box, index int, s Series, yrange Range) {
-	if c.FinalValueLabel.Show {
-		_, lv := s.GetValue(s.Len() - 1)
-		ll := yrange.Format(lv)
-
-		py := canvasBox.Top
-		ly := yrange.Translate(lv) + py
-
-		r.SetFontSize(c.FinalValueLabel.GetFontSize(DefaultFinalLabelFontSize))
-		textWidth, _ := r.MeasureText(ll)
-		textHeight := int(math.Floor(DefaultFinalLabelFontSize))
-		halfTextHeight := textHeight >> 1
-
-		asw := 0
-		if c.Axes.Show {
-			asw = int(c.Axes.GetStrokeWidth(DefaultAxisLineWidth))
-		}
-
-		cx := canvasBox.Right + asw
-
-		pt := c.FinalValueLabel.Padding.GetTop(DefaultFinalLabelPadding.Top)
-		pl := c.FinalValueLabel.Padding.GetLeft(DefaultFinalLabelPadding.Left)
-		pr := c.FinalValueLabel.Padding.GetRight(DefaultFinalLabelPadding.Right)
-		pb := c.FinalValueLabel.Padding.GetBottom(DefaultFinalLabelPadding.Bottom)
-
-		textX := cx + pl + DefaultFinalLabelDeltaWidth
-		textY := ly + halfTextHeight
-
-		ltlx := cx + pl + DefaultFinalLabelDeltaWidth
-		ltly := ly - (pt + halfTextHeight)
-
-		ltrx := cx + pl + pr + textWidth
-		ltry := ly - (pt + halfTextHeight)
-
-		lbrx := cx + pl + pr + textWidth
-		lbry := ly + (pb + halfTextHeight)
-
-		lblx := cx + DefaultFinalLabelDeltaWidth
-		lbly := ly + (pb + halfTextHeight)
-
-		//draw the shape...
-		r.SetFillColor(c.FinalValueLabel.GetFillColor(DefaultFinalLabelBackgroundColor))
-		r.SetStrokeColor(c.FinalValueLabel.GetStrokeColor(s.GetStyle().GetStrokeColor(GetDefaultSeriesStrokeColor(index))))
-		r.SetStrokeWidth(c.FinalValueLabel.GetStrokeWidth(DefaultAxisLineWidth))
-		r.MoveTo(cx, ly)
-		r.LineTo(ltlx, ltly)
-		r.LineTo(ltrx, ltry)
-		r.LineTo(lbrx, lbry)
-		r.LineTo(lblx, lbly)
-		r.LineTo(cx, ly)
-		r.Close()
-		r.FillStroke()
-
-		r.SetFontColor(c.FinalValueLabel.GetFontColor(DefaultTextColor))
-		r.Text(ll, textX, textY)
-	}
 }
 
 func (c Chart) drawTitle(r Renderer) error {

continuous_series.go

@@ -0,0 +1,70 @@
+package chart
+
+import (
+	"fmt"
+
+	"github.com/blendlabs/go-util"
+)
+
+// ContinuousSeries represents a line on a chart.
+type ContinuousSeries struct {
+	Name            string
+	Style           Style
+	FinalValueLabel Style
+
+	XValues []float64
+	YValues []float64
+}
+
+// GetName returns the name of the time series.
+func (cs ContinuousSeries) GetName() string {
+	return cs.Name
+}
+
+// GetStyle returns the line style.
+func (cs ContinuousSeries) GetStyle() Style {
+	return cs.Style
+}
+
+// Len returns the number of elements in the series.
+func (cs ContinuousSeries) Len() int {
+	return len(cs.XValues)
+}
+
+// GetValue gets a value at a given index.
+func (cs ContinuousSeries) GetValue(index int) (float64, float64) {
+	return cs.XValues[index], cs.YValues[index]
+}
+
+// GetXFormatter returns the xs value formatter.
+func (cs ContinuousSeries) GetXFormatter() Formatter {
+	return func(v interface{}) string {
+		if typed, isTyped := v.(float64); isTyped {
+			return fmt.Sprintf("%0.2f", typed)
+		}
+		return util.StringEmpty
+	}
+}
+
+// GetYFormatter returns the y value formatter.
+func (cs ContinuousSeries) GetYFormatter() Formatter {
+	return cs.GetXFormatter()
+}
+
+// Render renders the series.
+func (cs ContinuousSeries) Render(c *Chart, r Renderer, canvasBox Box, xrange, yrange Range) error {
+	DrawLineSeries(c, r, canvasBox, xrange, yrange, cs)
+
+	if cs.FinalValueLabel.Show {
+		asw := 0
+		if c.Axes.Show {
+			asw = int(c.Axes.GetStrokeWidth(DefaultAxisLineWidth))
+		}
+
+		_, lv := cs.GetValue(cs.Len() - 1)
+		ll := yrange.Format(lv)
+		lx := canvasBox.Right + asw
+		ly := yrange.Translate(lv) + canvasBox.Top
+		DrawAnnotation(c, r, canvasBox, xrange, yrange, cs.FinalValueLabel, lx, ly, ll)
+	}
+}

defaults.go

@@ -24,14 +24,16 @@ const (
 	DefaultFontSize = 10.0
 	// DefaultTitleFontSize is the default title font size.
 	DefaultTitleFontSize = 18.0
-	// DefaultFinalLabelDeltaWidth is the width of the left triangle out of the final label.
+	// DefaultAnnotationDeltaWidth is the width of the left triangle out of annotations.
-	DefaultFinalLabelDeltaWidth = 10
+	DefaultAnnotationDeltaWidth = 10
-	// DefaultFinalLabelFontSize is the font size of the final label.
+	// DefaultAnnotationFontSize is the font size of annotations.
-	DefaultFinalLabelFontSize = 10.0
+	DefaultAnnotationFontSize = 10.0
 	// DefaultAxisFontSize is the font size of the axis labels.
 	DefaultAxisFontSize = 10.0
 	// DefaultTitleTop is the default distance from the top of the chart to put the title.
 	DefaultTitleTop = 10
+	// DefaultYAxisMargin is the default distance from the right of the canvas to the y axis labels.
+	DefaultYAxisMargin = 5
 	// DefaultXAxisMargin is the default distance from bottom of the canvas to the x axis labels.
 	DefaultXAxisMargin = 10
 	// DefaultMinimumTickHorizontalSpacing is the minimum distance between horizontal ticks.
@@ -69,8 +71,8 @@ var (
 	// DefaultFillColor is the default fill color.
 	// It is equivalent to #0074d9.
 	DefaultFillColor = drawing.Color{R: 0, G: 217, B: 116, A: 255}
-	// DefaultFinalLabelBackgroundColor is the default final label background color.
+	// DefaultAnnotationFillColor is the default annotation background color.
-	DefaultFinalLabelBackgroundColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
+	DefaultAnnotationFillColor = drawing.Color{R: 255, G: 255, B: 255, A: 255}
 )
 
 var (
@@ -90,8 +92,8 @@ func GetDefaultSeriesStrokeColor(index int) drawing.Color {
 }
 
 var (
-	// DefaultFinalLabelPadding is the padding around the final label.
+	// DefaultAnnotationPadding is the padding around an annotation.
-	DefaultFinalLabelPadding = Box{Top: 5, Left: 0, Right: 7, Bottom: 5}
+	DefaultAnnotationPadding = Box{Top: 5, Left: 0, Right: 7, Bottom: 5}
 	// DefaultBackgroundPadding is the default canvas padding config.
 	DefaultBackgroundPadding = Box{Top: 5, Left: 5, Right: 5, Bottom: 5}
 )

series.go

@@ -1,121 +1,117 @@
 package chart
 
-import (
+import "math"
-	"fmt"
-	"time"
 
-	"github.com/blendlabs/go-util"
+// Series is a entity data set. It constitutes an item to draw on the chart.
-)
+// The series interface is the bare minimum you need to implement to draw something on a chart.
-
-// Series is a entity data set.
 type Series interface {
 	GetName() string
 	GetStyle() Style
+	Render(c *Chart, r Renderer, canvasBox Box, xrange, yrange Range) error
+}
+
+// ValueProvider is a series that is a set of values.
+type ValueProvider interface {
 	Len() int
-
 	GetValue(index int) (float64, float64)
+}
 
+// FormatterProvider is a series that has custom formatters.
+type FormatterProvider interface {
 	GetXFormatter() Formatter
 	GetYFormatter() Formatter
 }
 
-// TimeSeries is a line on a chart.
+// DrawLineSeries draws a line series with a renderer.
-type TimeSeries struct {
+func DrawLineSeries(c *Chart, r Renderer, canvasBox Box, xrange, yrange Range, vs ValueProvider) error {
-	Name  string
+	if vs.Len() == 0 {
-	Style Style
+		return
-
-	XValues []time.Time
-	YValues []float64
-}
-
-// GetName returns the name of the time series.
-func (ts TimeSeries) GetName() string {
-	return ts.Name
-}
-
-// GetStyle returns the line style.
-func (ts TimeSeries) GetStyle() Style {
-	return ts.Style
-}
-
-// Len returns the number of elements in the series.
-func (ts TimeSeries) Len() int {
-	return len(ts.XValues)
-}
-
-// GetValue gets a value at a given index.
-func (ts TimeSeries) GetValue(index int) (x float64, y float64) {
-	x = float64(ts.XValues[index].Unix())
-	y = ts.YValues[index]
-	return
-}
-
-// GetXFormatter returns the x value formatter.
-func (ts TimeSeries) GetXFormatter() Formatter {
-	return func(v interface{}) string {
-		if typed, isTyped := v.(time.Time); isTyped {
-			return typed.Format(DefaultDateFormat)
-		}
-		if typed, isTyped := v.(int64); isTyped {
-			return time.Unix(typed, 0).Format(DefaultDateFormat)
-		}
-		if typed, isTyped := v.(float64); isTyped {
-			return time.Unix(int64(typed), 0).Format(DefaultDateFormat)
-		}
-		return util.StringEmpty
 	}
-}
 
-// GetYFormatter returns the y value formatter.
+	cx := canvasBox.Left
-func (ts TimeSeries) GetYFormatter() Formatter {
+	cy := canvasBox.Top
-	return func(v interface{}) string {
+	cb := canvasBox.Bottom
-		if typed, isTyped := v.(float64); isTyped {
+	cw := canvasBox.Width
-			return fmt.Sprintf("%0.2f", typed)
+
+	v0x, v0y := vs.GetValue(0)
+	x0 := cw - xrange.Translate(v0x)
+	y0 := yrange.Translate(v0y)
+
+	var vx, vy float64
+	var x, y int
+
+	fill := s.GetStyle().GetFillColor()
+	if !fill.IsZero() {
+		r.SetFillColor(fill)
+		r.MoveTo(x0+cx, y0+cy)
+		for i := 1; i < vs.Len(); i++ {
+			vx, vy = vs.GetValue(i)
+			x = cw - xrange.Translate(vx)
+			y = yrange.Translate(vy)
+			r.LineTo(x+cx, y+cy)
 		}
-		return util.StringEmpty
+		r.LineTo(x+cx, cb)
+		r.LineTo(x0+cx, cb)
+		r.Close()
+		r.Fill()
 	}
-}
 
-// ContinuousSeries represents a line on a chart.
+	stroke := s.GetStyle().GetStrokeColor(GetDefaultSeriesStrokeColor(index))
-type ContinuousSeries struct {
+	r.SetStrokeColor(stroke)
-	Name  string
+	r.SetStrokeWidth(s.GetStyle().GetStrokeWidth(DefaultStrokeWidth))
-	Style Style
 
-	XValues []float64
+	r.MoveTo(x0+cx, y0+cy)
-	YValues []float64
+	for i := 1; i < vs.Len(); i++ {
-}
+		vx, vy = vs.GetValue(i)
-
+		x = cw - xrange.Translate(vx)
-// GetName returns the name of the time series.
+		y = yrange.Translate(vy)
-func (cs ContinuousSeries) GetName() string {
+		r.LineTo(x+cx, y+cy)
-	return cs.Name
-}
-
-// GetStyle returns the line style.
-func (cs ContinuousSeries) GetStyle() Style {
-	return cs.Style
-}
-
-// Len returns the number of elements in the series.
-func (cs ContinuousSeries) Len() int {
-	return len(cs.XValues)
-}
-
-// GetValue gets a value at a given index.
-func (cs ContinuousSeries) GetValue(index int) (float64, float64) {
-	return cs.XValues[index], cs.YValues[index]
-}
-
-// GetXFormatter returns the xs value formatter.
-func (cs ContinuousSeries) GetXFormatter() Formatter {
-	return func(v interface{}) string {
-		if typed, isTyped := v.(float64); isTyped {
-			return fmt.Sprintf("%0.2f", typed)
-		}
-		return util.StringEmpty
 	}
+	r.Stroke()
 }
 
-// GetYFormatter returns the y value formatter.
+// DrawAnnotation draws an anotation with a renderer.
-func (cs ContinuousSeries) GetYFormatter() Formatter {
+func DrawAnnotation(c *Chart, r Renderer, canvasBox Box, xrange, yrange, s Style, lx, ly int, lv string) {
-	return cs.GetXFormatter()
+	py := canvasBox.Top
+
+	r.SetFontSize(s.GetFontSize(DefaultFinalLabelFontSize))
+	textWidth, _ := r.MeasureText(ll)
+	textHeight := int(math.Floor(DefaultFinalLabelFontSize))
+	halfTextHeight := textHeight >> 1
+
+	pt := s.Padding.GetTop(DefaultFinalLabelPadding.Top)
+	pl := s.Padding.GetLeft(DefaultFinalLabelPadding.Left)
+	pr := s.Padding.GetRight(DefaultFinalLabelPadding.Right)
+	pb := s.Padding.GetBottom(DefaultFinalLabelPadding.Bottom)
+
+	textX := lx + pl + DefaultFinalLabelDeltaWidth
+	textY := ly + halfTextHeight
+
+	ltlx := lx + pl + DefaultFinalLabelDeltaWidth
+	ltly := ly - (pt + halfTextHeight)
+
+	ltrx := lx + pl + pr + textWidth
+	ltry := ly - (pt + halfTextHeight)
+
+	lbrx := lx + pl + pr + textWidth
+	lbry := ly + (pb + halfTextHeight)
+
+	lblx := lx + DefaultFinalLabelDeltaWidth
+	lbly := ly + (pb + halfTextHeight)
+
+	//draw the shape...
+	r.SetFillColor(s.GetFillColor(DefaultAnnotationFillColor))
+	r.SetStrokeColor(s.GetStrokeColor())
+	r.SetStrokeWidth(s.GetStrokeWidth())
+	r.MoveTo(lx, ly)
+	r.LineTo(ltlx, ltly)
+	r.LineTo(ltrx, ltry)
+	r.LineTo(lbrx, lbry)
+	r.LineTo(lblx, lbly)
+	r.LineTo(cx, ly)
+	r.Close()
+	r.FillStroke()
+
+	r.SetFontColor(s.GetFontColor(DefaultTextColor))
+	r.Text(ll, textX, textY)
 }

time_series.go

@@ -0,0 +1,66 @@
+package chart
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/blendlabs/go-util"
+)
+
+// TimeSeries is a line on a chart.
+type TimeSeries struct {
+	Name            string
+	Style           Style
+	FinalValueLabel Style
+
+	XValues []time.Time
+	YValues []float64
+}
+
+// GetName returns the name of the time series.
+func (ts TimeSeries) GetName() string {
+	return ts.Name
+}
+
+// GetStyle returns the line style.
+func (ts TimeSeries) GetStyle() Style {
+	return ts.Style
+}
+
+// Len returns the number of elements in the series.
+func (ts TimeSeries) Len() int {
+	return len(ts.XValues)
+}
+
+// GetValue gets a value at a given index.
+func (ts TimeSeries) GetValue(index int) (x float64, y float64) {
+	x = float64(ts.XValues[index].Unix())
+	y = ts.YValues[index]
+	return
+}
+
+// GetXFormatter returns the x value formatter.
+func (ts TimeSeries) GetXFormatter() Formatter {
+	return func(v interface{}) string {
+		if typed, isTyped := v.(time.Time); isTyped {
+			return typed.Format(DefaultDateFormat)
+		}
+		if typed, isTyped := v.(int64); isTyped {
+			return time.Unix(typed, 0).Format(DefaultDateFormat)
+		}
+		if typed, isTyped := v.(float64); isTyped {
+			return time.Unix(int64(typed), 0).Format(DefaultDateFormat)
+		}
+		return util.StringEmpty
+	}
+}
+
+// GetYFormatter returns the y value formatter.
+func (ts TimeSeries) GetYFormatter() Formatter {
+	return func(v interface{}) string {
+		if typed, isTyped := v.(float64); isTyped {
+			return fmt.Sprintf("%0.2f", typed)
+		}
+		return util.StringEmpty
+	}
+}

time_series_test.go

@@ -0,0 +1,30 @@
+package chart
+
+import (
+	"testing"
+	"time"
+
+	"github.com/blendlabs/go-assert"
+)
+
+func TestTimeSeriesGetValue(t *testing.T) {
+	assert := assert.New(t)
+
+	ts := TimeSeries{
+		Name: "Test",
+		XValues: []time.Time{
+			time.Now().AddDate(0, 0, -5),
+			time.Now().AddDate(0, 0, -4),
+			time.Now().AddDate(0, 0, -3),
+			time.Now().AddDate(0, 0, -2),
+			time.Now().AddDate(0, 0, -1),
+		},
+		YValues: []float64{
+			1.0, 2.0, 3.0, 4.0, 5.0,
+		},
+	}
+
+	x0, y0 := ts.GetValue(0)
+	assert.NotZero(x0)
+	assert.Equal(1.0, y0)
+}