adds a rerender example

_examples/rerender/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/wcharczuk/go-chart/util"
+
+	chart "github.com/wcharczuk/go-chart"
+)
+
+var lock sync.Mutex
+var graph *chart.Chart
+var ts *chart.TimeSeries
+
+func addData(t time.Time, e time.Duration) {
+	lock.Lock()
+	ts.XValues = append(ts.XValues, t)
+	ts.YValues = append(ts.YValues, util.Time.Millis(e))
+	lock.Unlock()
+}
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	start := time.Now()
+	defer func() {
+		addData(start, time.Since(start))
+	}()
+	if len(ts.XValues) == 0 {
+		http.Error(res, "no data (yet)", http.StatusBadRequest)
+		return
+	}
+	res.Header().Set("Content-Type", "image/png")
+	if err := graph.Render(chart.PNG, res); err != nil {
+		log.Printf("%v", err)
+	}
+}
+
+func main() {
+	ts = &chart.TimeSeries{
+		XValues: []time.Time{},
+		YValues: []float64{},
+	}
+	graph = &chart.Chart{
+		Series: []chart.Series{ts},
+	}
+	http.HandleFunc("/", drawChart)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

util/time.go

@@ -9,6 +9,11 @@ var (
 
 type timeUtil struct{}
 
+// Millis returns the duration as milliseconds.
+func (tu timeUtil) Millis(d time.Duration) float64 {
+	return float64(d) / float64(time.Millisecond)
+}
+
 // TimeToFloat64 returns a float64 representation of a time.
 func (tu timeUtil) ToFloat64(t time.Time) float64 {
 	return float64(t.UnixNano())