add custom value formatters for continuous series.

continuous_series.go

@@ -7,6 +7,9 @@ type ContinuousSeries struct {
 
 	YAxis YAxisType
 
+	XValueFormatter ValueFormatter
+	YValueFormatter ValueFormatter
+
 	XValues []float64
 	YValues []float64
 }
@@ -38,8 +41,16 @@ func (cs ContinuousSeries) GetLastValue() (float64, float64) {
 
 // GetValueFormatters returns value formatter defaults for the series.
 func (cs ContinuousSeries) GetValueFormatters() (x, y ValueFormatter) {
-	x = FloatValueFormatter
-	y = FloatValueFormatter
+	if cs.XValueFormatter != nil {
+		x = cs.XValueFormatter
+	} else {
+		x = FloatValueFormatter
+	}
+	if cs.YValueFormatter != nil {
+		y = cs.YValueFormatter
+	} else {
+		y = FloatValueFormatter
+	}
 	return
 }
 

continuous_series_test.go

@@ -1,6 +1,7 @@
 package chart
 
 import (
+	"fmt"
 	"testing"
 
 	assert "github.com/blendlabs/go-assert"
@@ -29,3 +30,20 @@ func TestContinuousSeries(t *testing.T) {
 	assert.Equal(10.0, xn)
 	assert.Equal(10.0, yn)
 }
+
+func TestContinuousSeriesValueFormatter(t *testing.T) {
+	assert := assert.New(t)
+
+	cs := ContinuousSeries{
+		XValueFormatter: func(v interface{}) string {
+			return fmt.Sprintf("%f foo", v)
+		},
+		YValueFormatter: func(v interface{}) string {
+			return fmt.Sprintf("%f bar", v)
+		},
+	}
+
+	xf, yf := cs.GetValueFormatters()
+	assert.Equal("0.100000 foo", xf(0.1))
+	assert.Equal("0.100000 bar", yf(0.1))
+}