axis labels!

chart.go

@@ -1,6 +1,7 @@
 package chart
 
 import (
+	"errors"
 	"io"
 	"math"
 
@@ -37,6 +38,9 @@ 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 {
+	if len(c.Series) == 0 {
+		return errors.New("Please provide at least one series")
+	}
 	r := provider(c.Width, c.Height)
 	if c.hasText() {
 		font, err := c.GetFont()
@@ -60,7 +64,15 @@ func (c *Chart) Render(provider RendererProvider, w io.Writer) error {
 }
 
 func (c Chart) hasText() bool {
-	return c.TitleStyle.Show || c.Axes.Show
+	return c.TitleStyle.Show || c.Axes.Show || c.FinalValueLabel.Show
+}
+
+func (c Chart) getAxisWidth() int {
+	asw := 0
+	if c.Axes.Show {
+		asw = int(c.Axes.GetStrokeWidth(DefaultAxisLineWidth))
+	}
+	return asw
 }
 
 func (c Chart) calculateCanvasBox(r Renderer) Box {
@@ -69,7 +81,11 @@ func (c Chart) calculateCanvasBox(r Renderer) Box {
 	if finalLabelWidth > dpr {
 		dpr = finalLabelWidth
 	}
+	axisBottomHeight := c.calculateBottomLabelHeight()
 	dpb := DefaultBackgroundPadding.Bottom
+	if dpb < axisBottomHeight {
+		dpb = axisBottomHeight
+	}
 
 	cb := Box{
 		Top:    c.Background.Padding.GetTop(DefaultBackgroundPadding.Top),
@@ -88,7 +104,8 @@ func (c Chart) calculateFinalLabelWidth(r Renderer) int {
 	}
 	var finalLabelText string
 	for _, s := range c.Series {
-		_, ll := s.GetLabel(s.Len() - 1)
+		_, lv := s.GetValue(s.Len() - 1)
+		ll := s.GetYFormatter()(lv)
 		if len(finalLabelText) < len(ll) {
 			finalLabelText = ll
 		}
@@ -96,11 +113,10 @@ func (c Chart) calculateFinalLabelWidth(r Renderer) int {
 
 	r.SetFontSize(c.FinalValueLabel.GetFontSize(DefaultFinalLabelFontSize))
 	textWidth := r.MeasureText(finalLabelText)
+	asw := c.getAxisWidth()
 
 	pl := c.FinalValueLabel.Padding.GetLeft(DefaultFinalLabelPadding.Left)
 	pr := c.FinalValueLabel.Padding.GetRight(DefaultFinalLabelPadding.Right)
-
-	asw := int(c.Axes.GetStrokeWidth(DefaultAxisLineWidth))
 	lsw := int(c.FinalValueLabel.GetStrokeWidth(DefaultAxisLineWidth))
 
 	return DefaultFinalLabelDeltaWidth +
@@ -108,6 +124,13 @@ func (c Chart) calculateFinalLabelWidth(r Renderer) int {
 		textWidth + asw + 2*lsw
 }
 
+func (c Chart) calculateBottomLabelHeight() int {
+	if c.Axes.Show {
+		return c.getAxisWidth() + int(math.Ceil(c.Axes.GetFontSize(DefaultAxisFontSize))) + DefaultXAxisMargin
+	}
+	return 0
+}
+
 func (c Chart) initRanges(canvasBox Box) (xrange Range, yrange Range) {
 	//iterate over each series, pull out the min/max for x,y
 	var didSetFirstValues bool
@@ -136,6 +159,8 @@ func (c Chart) initRanges(canvasBox Box) (xrange Range, yrange Range) {
 				didSetFirstValues = true
 			}
 		}
+		xrange.Formatter = s.GetXFormatter()
+		yrange.Formatter = s.GetYFormatter()
 	}
 
 	if c.XRange.IsZero() {
@@ -194,13 +219,74 @@ func (c Chart) drawAxes(r Renderer, canvasBox Box, xrange, yrange Range) {
 		r.LineTo(canvasBox.Right, canvasBox.Top)
 		r.Stroke()
 
-		c.drawAxesLabels(r, xrange, yrange)
+		c.drawXAxisLabels(r, canvasBox, xrange)
+		c.drawYAxisLabels(r, canvasBox, yrange)
 	}
 }
 
-func (c Chart) drawAxesLabels(r Renderer, xrange, yrange Range) {
+func (c Chart) drawYAxisLabels(r Renderer, canvasBox Box, yrange Range) {
-	// do x axis
+	tickFontSize := c.Axes.GetFontSize(DefaultAxisFontSize)
-	// do y axis
+
+	r.SetFontColor(c.Axes.GetFontColor(DefaultAxisColor))
+	r.SetFontSize(tickFontSize)
+
+	minimumTickHeight := tickFontSize + DefaultMinimumTickVerticalSpacing
+	tickCount := int(math.Floor(float64(yrange.Domain) / float64(minimumTickHeight)))
+
+	if tickCount > DefaultMaxTickCount {
+		tickCount = DefaultMaxTickCount
+	}
+
+	rangeTicks := Slices(tickCount, yrange.Max-yrange.Min)
+	domainTicks := Slices(tickCount, float64(yrange.Domain))
+
+	asw := c.getAxisWidth()
+	tx := canvasBox.Right + DefaultFinalLabelDeltaWidth + asw
+
+	count := len(rangeTicks)
+	if len(domainTicks) < count {
+		count = len(domainTicks) //guard against mismatched array sizes.
+	}
+
+	for index := 0; index < count; index++ {
+		v := rangeTicks[index]
+		y := domainTicks[index]
+		ty := canvasBox.Bottom - int(y)
+		r.Text(yrange.Format(v), tx, ty)
+	}
+}
+
+func (c Chart) drawXAxisLabels(r Renderer, canvasBox Box, xrange Range) {
+	tickFontSize := c.Axes.GetFontSize(DefaultAxisFontSize)
+
+	r.SetFontColor(c.Axes.GetFontColor(DefaultAxisColor))
+	r.SetFontSize(tickFontSize)
+
+	maxLabelWidth := 60
+
+	minimumTickWidth := maxLabelWidth + DefaultMinimumTickHorizontalSpacing
+	tickCount := int(math.Floor(float64(xrange.Domain) / float64(minimumTickWidth)))
+
+	if tickCount > DefaultMaxTickCount {
+		tickCount = DefaultMaxTickCount
+	}
+
+	rangeTicks := Slices(tickCount, xrange.Max-xrange.Min)
+	domainTicks := Slices(tickCount, float64(xrange.Domain))
+
+	ty := canvasBox.Bottom + DefaultXAxisMargin + int(tickFontSize)
+
+	count := len(rangeTicks)
+	if len(domainTicks) < count {
+		count = len(domainTicks) //guard against mismatched array sizes.
+	}
+
+	for index := 0; index < count; index++ {
+		v := rangeTicks[index] + xrange.Min
+		x := domainTicks[index]
+		tx := canvasBox.Left + int(x)
+		r.Text(xrange.Format(v), tx, ty)
+	}
 }
 
 func (c Chart) drawSeries(r Renderer, canvasBox Box, index int, s Series, xrange, yrange Range) {
@@ -236,7 +322,7 @@ func (c Chart) drawSeries(r Renderer, canvasBox Box, index int, s Series, xrange
 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 := s.GetLabel(s.Len() - 1)
+		ll := s.GetYFormatter()(lv)
 
 		py := canvasBox.Top
 		ly := yrange.Translate(lv) + py
@@ -246,7 +332,12 @@ func (c Chart) drawFinalValueLabel(r Renderer, canvasBox Box, index int, s Serie
 		textHeight := int(math.Floor(DefaultFinalLabelFontSize))
 		halfTextHeight := textHeight >> 1
 
-		cx := canvasBox.Right + int(c.Axes.GetStrokeWidth(DefaultAxisLineWidth))
+		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)

defaults.go

@@ -28,10 +28,20 @@ const (
 	DefaultFinalLabelDeltaWidth = 10
 	// DefaultFinalLabelFontSize is the font size of the final label.
 	DefaultFinalLabelFontSize = 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
+	// 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.
+	DefaultMinimumTickHorizontalSpacing = 20
+	// DefaultMinimumTickVerticalSpacing is the minimum distance between vertical ticks.
+	DefaultMinimumTickVerticalSpacing = 20
 	// DefaultDateFormat is the default date format.
 	DefaultDateFormat = "2006-01-02"
+	// DefaultMaxTickCount is the maximum number of ticks to draw
+	DefaultMaxTickCount = 7
 )
 
 var (

formatter.go

@@ -0,0 +1,4 @@
+package chart
+
+// Formatter is a function that takes a value and produces a string.
+type Formatter func(v interface{}) string

range.go

@@ -3,6 +3,8 @@ package chart
 import (
 	"fmt"
 	"math"
+
+	"github.com/blendlabs/go-util"
 )
 
 // Range represents a continuous range,
@@ -10,6 +12,7 @@ type Range struct {
 	Min       float64
 	Max       float64
 	Domain    int
+	Formatter Formatter
 }
 
 // IsZero returns if the range has been set or not.
@@ -27,6 +30,14 @@ func (r Range) String() string {
 	return fmt.Sprintf("Range [%.2f,%.2f] => %d", r.Min, r.Max, r.Domain)
 }
 
+// Format formats the value based on the range's formatter.
+func (r Range) Format(v interface{}) string {
+	if r.Formatter != nil {
+		return r.Formatter(v)
+	}
+	return util.StringEmpty
+}
+
 // Translate maps a given value into the range space.
 // An example would be a 600 px image, with a min of 10 and a max of 100.
 // Translate(50) would yield (50.0/90.0)*600 ~= 333.33

series.go

@@ -3,6 +3,8 @@ package chart
 import (
 	"fmt"
 	"time"
+
+	"github.com/blendlabs/go-util"
 )
 
 // Series is a entity data set.
@@ -10,8 +12,11 @@ type Series interface {
 	GetName() string
 	GetStyle() Style
 	Len() int
+
 	GetValue(index int) (float64, float64)
-	GetLabel(index int) (string, string)
+
+	GetXFormatter() Formatter
+	GetYFormatter() Formatter
 }
 
 // TimeSeries is a line on a chart.
@@ -45,11 +50,30 @@ func (ts TimeSeries) GetValue(index int) (x float64, y float64) {
 	return
 }
 
-// GetLabel gets a label for the values at a given index.
+// GetXFormatter returns the x value formatter.
-func (ts TimeSeries) GetLabel(index int) (xLabel string, yLabel string) {
+func (ts TimeSeries) GetXFormatter() Formatter {
-	xLabel = ts.XValues[index].Format(DefaultDateFormat)
+	return func(v interface{}) string {
-	yLabel = fmt.Sprintf("%0.2f", ts.YValues[index])
+		if typed, isTyped := v.(time.Time); isTyped {
-	return
+			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
+	}
 }
 
 // ContinousSeries represents a line on a chart.
@@ -81,9 +105,17 @@ func (cs ContinousSeries) GetValue(index int) (interface{}, float64) {
 	return cs.XValues[index], cs.YValues[index]
 }
 
-// GetLabel gets a label for the values at a given index.
+// GetXFormatter returns the xs value formatter.
-func (cs ContinousSeries) GetLabel(index int) (xLabel string, yLabel string) {
+func (cs ContinousSeries) GetXFormatter() Formatter {
-	xLabel = fmt.Sprintf("%0.2f", cs.XValues[index])
+	return func(v interface{}) string {
-	yLabel = fmt.Sprintf("%0.2f", cs.YValues[index])
+		if typed, isTyped := v.(float64); isTyped {
-	return
+			return fmt.Sprintf("%0.2f", typed)
+		}
+		return util.StringEmpty
+	}
+}
+
+// GetYFormatter returns the y value formatter.
+func (cs ContinousSeries) GetYFormatter() Formatter {
+	return cs.GetXFormatter()
 }

testserver/main.go

@@ -21,8 +21,8 @@ func main() {
 			TitleStyle: chart.Style{
 				Show: true,
 			},
-			Width:  800,
+			Width:  640,
-			Height: 380,
+			Height: 480,
 			Axes: chart.Style{
 				Show:        true,
 				StrokeWidth: 1.0,

util.go

@@ -3,7 +3,6 @@ package chart
 import (
 	"fmt"
 	"image/color"
-	"math"
 	"time"
 )
 
@@ -58,10 +57,10 @@ func MinAndMaxOfTime(values ...time.Time) (min time.Time, max time.Time) {
 
 // Slices generates N slices that span the total.
 // The resulting array will be intermediate indexes until total.
-func Slices(count, total int) []int {
+func Slices(count int, total float64) []float64 {
-	var values []int
+	var values []float64
-	sliceWidth := int(math.Floor(float64(total) / float64(count)))
+	sliceWidth := float64(total) / float64(count)
-	for cursor := 0; cursor < total; cursor += sliceWidth {
+	for cursor := 0.0; cursor < total; cursor += sliceWidth {
 		values = append(values, cursor)
 	}
 	return values