Benchmarking the performance of drawing line charts. (#30)

* Another example for benchmarking the performance of drawing line charts.

* Cleanup the code a bit.

_examples/benchmark_line_charts/main.go

@@ -0,0 +1,73 @@
+// Usage: http://localhost:8080?series=100&values=1000
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func random(min, max float64) float64 {
+	return rand.Float64()*(max-min) + min
+}
+
+func drawLargeChart(res http.ResponseWriter, r *http.Request) {
+	numSeriesInt64, err := strconv.ParseInt(r.FormValue("series"), 10, 64)
+	if err != nil {
+		numSeriesInt64 = int64(1)
+	}
+	numSeries := int(numSeriesInt64)
+
+	numValuesInt64, err := strconv.ParseInt(r.FormValue("values"), 10, 64)
+	if err != nil {
+		numValuesInt64 = int64(100)
+	}
+	numValues := int(numValuesInt64)
+
+	series := make([]chart.Series, numSeries)
+
+	for i := 0; i < numSeries; i++ {
+		xValues := make([]time.Time, numValues)
+		yValues := make([]float64, numValues)
+
+		for j := 0; j < numValues; j++ {
+			xValues[j] = time.Now().AddDate(0, 0, (numValues-j)*-1)
+			yValues[j] = random(float64(-500), float64(500))
+		}
+
+		series[i] = chart.TimeSeries{
+			Name:    fmt.Sprintf("aaa.bbb.hostname-%v.ccc.ddd.eee.fff.ggg.hhh.iii.jjj.kkk.lll.mmm.nnn.value", i),
+			XValues: xValues,
+			YValues: yValues,
+		}
+	}
+
+	graph := chart.Chart{
+		XAxis: chart.XAxis{
+			Name:      "Time",
+			NameStyle: chart.StyleShow(),
+			Style:     chart.StyleShow(),
+		},
+		YAxis: chart.YAxis{
+			Name:      "Value",
+			NameStyle: chart.StyleShow(),
+			Style:     chart.StyleShow(),
+		},
+		Series: series,
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	graph.Render(chart.PNG, res)
+}
+
+func main() {
+	http.HandleFunc("/", drawLargeChart)
+	http.HandleFunc("/favico.ico", func(res http.ResponseWriter, req *http.Request) {
+		res.Write([]byte{})
+	})
+	http.ListenAndServe(":8080", nil)
+}